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Gallery, Projects and General => Project Logs => Topic started by: sorveltaja on October 26, 2019, 07:15:55 PM

Title: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on October 26, 2019, 07:15:55 PM
There is surprisingly low amount of information about the subject on the net. Yes, I'm aware, that there are commercially made optical pickups for guitars and basses.

But that's not what I'm after. What I'm after, is to expand the soundscape of electric guitar, in analog way, doing it using(hopefully) easily available components.

To be specific, my aim is to make a hexaphonic pickup, that has separate output for each guitar string.

In the past, I made hand-wound coils for each string, but their output was very weak, so I buried the project.

I have to say, that I'm not an artist, or electrician, so I probably butcher every one of the rules involved.

But, besides of that, I can see the reason, why there is so little info about making optical pickups on the net.
When there is practically nothing to look for, you have to try it for yourself. That's where it gets really challenging. Not only that, but hexaphonic pickup needs same circuit for each string.

I have done some testings with different setups, using 3mm infrared leds, and -receivers. Somewhat engouraging, as the crosstalk between strings is extremely low, not even noticeable, when listening to the output. But those infrared leds, and -receivers do not produce equal output. More on that later.

Unfortunately no pics yet, and I know this thread is useless without them. Will post them soon.

If nothing else, I hope to bring out positives and negatives, that noob like me faces on project like this. I have no idea, where it leads, but anyways, journey has started.




 
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on October 27, 2019, 04:20:01 PM
Here is the current setup, that has 3mm infrared leds and phototransistors paired, so that they can be plugged in or out separately, if it is needed. IR components are press fitted.

Parts holding them are 3d-printed, also press fitted to the base, as they would be very tricky to machine, because every pair has to have different height, corresponding to that string.

Meaning, that the led's and phototransistors "eyes" should be at the very same level with the string, to create a maximum "disturbance" in the infrared light, that travels from the led to the receiving phototransistor, providing the output:
(http://www.elisanet.fi/kz1706/optical_pup/current_setup.png)

Hopefully bit more clearer picture, as in the above pic, the ends of the IR components have been painted to prevent the "shine through" -effect:
(http://www.elisanet.fi/kz1706/optical_pup/current_setup_cad.png) 

There are plenty of configurations, of how the IR components could be arranged. At the moment, I use the horizontal one, because the string doesn't disappear from the IR beam, when bending it.
Vertical one cuts out immediately, unless there are multiple IR component pairs for each string.

For testing purposes, I'll try to make every consisting parts, and stages as "modular" as I can.

This earlier contraption has practically the same configuration of components, as above, but they are all part of... one part.
Addition to that, I used superglue to secure them in place. All seemed jolly good, until I tested the outputs. There was nothing to write home about.
(http://www.elisanet.fi/kz1706/optical_pup/failed_attempt.png)

Closer inspection revealed, that all the IR component's "eye" -surfaces had gone dull, because of the cyanoacrylate fumes (http://emoticons4u.com/crazy/1087.gif).
As one might guess, none of those parts are "serviceable" anymore.

Fortunately basic IR components aren't that expensive, neither is the PLA for the 3d-printer.

Next comes the "interfacing" with a guitar, while testing. I haven't yet found a way to "surface mount" all the possible electronics, without disturbing the guitar's delicate, inner self.

If one wants to take the step, to test out the consepts mentioned, be sure to have a sacrificial guitar, that doesn't mind the few extra holes drilled through it.

I think the interfacing is very important, to assure, that the IR components stay in place during all the tests.

I made a cavity to the back of the guitar, to have enough space for two small circuit boards. I used paint to attach aluminum foil to the surface, just in case, that the grounding is needed:
(http://www.elisanet.fi/kz1706/optical_pup/back_of_the_guitar_2.png)

There are 12 holes, that go through the wood:
(http://www.elisanet.fi/kz1706/optical_pup/back_of_the_guitar_cad.png)
 
That way, there is something to attach the phototransistor's leads, instead of them moving wildly around. Longer leads belong to the IR leds, and are wired in series, instead of earlier, parallel configuration.
--------------------------------------------------------------------

Feeding the IR leds is somewhat confusing for me. While wired parallel, there was big differences between their interaction with phototransistors, so much that every one of them required "tuning", and still didn't deliver other than unwanted noise for the receiving component.

Series config offered pretty much the same results. All that was done using plain DC for the leds.

Seems that it wasn't enough to keep the phototransistors busy enough, to keep them from observing the background noises.

More on that in the next posting. 

Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: RussellT on October 28, 2019, 05:52:28 AM
I'm curious, why is an optical pickup better? And aren't you making it more difficult by working so close to the end of the string?

Russell
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: russ57 on October 28, 2019, 07:18:02 AM
I'm curious as well, but I guess it's just another thing I've never heard of.

I would expect you would need a very narrow beam in order to detect the movement of the string, so as it vibrates it can cut off the beam. So the beam would need to be at right angles to the vibration of the string.
Is it vibration parallel to the body or perpendicular? I would think parallel?





Russ

Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: philf on October 28, 2019, 08:54:21 AM
I too wondered what the advantage could be and found this:

https://www.willcoxguitars.com/lightwave-optical-pickup-system/ (https://www.willcoxguitars.com/lightwave-optical-pickup-system/)

"Music at the Speed of Light
The optical pickup is a proprietary type of transducer which utilizes an infrared emitter and an array of photodetectors for each string. The emitter casts a shadow of the string onto the photodetectors. As the string vibrates, the size and shape of the shadow changes accordingly and modulates a current which passes through the photodetectors. This current is the analog electrical signal which represents an accurate depiction of the vibrating string."

I do wonder if the ordinary listener would be able to detect any difference.

Phil.

Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: Will_D on October 28, 2019, 04:42:26 PM
I would think that the optical method will work with any string as opposed to the electro-mechanical pickup that only works with a metallic string

As I am in no way musical the above may be pure BS
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on October 28, 2019, 06:13:01 PM
Thanks for the replies. RussellT, optical pickup isn't necessary better than the ordinary electromagnetic one.

Reason, that I chose optical pickups, is that they are much more compact, and ready to be used as sensors.
Electromagnetic pickups require very precise winding of really thin copper wire, to produce good output. Naturally, space between the strings limit the size of those type pickups.

Not only that, but when one wants to make a polyphonic pickup, six separate elements are needed for guitar.

What do I mean by polyphonic pickup, and what is its purpose?

The consept comes from commercial guitar synthesizers, that have a specific, polyphonic pickups.   
Although that kind of pickups can be bought separately, unfortunately they require a model specific synthesizer device to work, which are rather expensive.

Difference between mono- and polyphonic pickups:
(http://www.elisanet.fi/kz1706/optical_pup/monophonic_vs_polyphonic.png)

So the polyphonic(or hexaphonic) pickup has six outputs, which each could be processed independently. For example, signal from one string could be panned to the left, and signal from other string to the right in the stereo field. Or each string could drive different oscillators. Almost endless amount of options.

What comes to the current setup, I placed the optical pickups near the end of the strings(bridge), so that they are not in a way, when plucking strings.
Obviously, string vibration is very faint at the end of the string, but even that minimal movement is enough for the IR receivers to pick up even the tiniest deviations in the IR light, that the leds produce.

Russ57, that is exactly, what I thought at first. That idea came from optical encoders, that use slotted wheels to interrupt the IR beam.
Then came the idea of using narrowed laser beams as a light source. But I think, that the light source should be infrared, according to commercial optical pickups.

Infrared laser is definitely no-no, as it is plain dangerous, making serious damage for the eyes, without proper safety precautions.

Philf, thanks for adding the quote. It pretty much tells the essential things about optical pickups.

Does the ordinary listener detect the difference? Not necessarily.
But If the guitar or bass has only optical pickup(s) in it, there isn't any magnetic pull from the electromagnetic pickups, that might dampen the sustain of the steel strings.

So I assume, that to tell the difference, you have to be either musician, or any other person, that had to develop their auditory senses, while working with the music.

Will_D, That's not BS. When using optical pickup(s), the string material can be something like nylon or rubber, or practically anything in a form of a string, that vibrates.


 
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: BillTodd on October 28, 2019, 06:21:42 PM
 If you want linearity from optical sensors, you might try to get a difference signal from two sensors  (such that the motion of the string covers one while exposing the other ) the differential approach will also remove overall illumination variance .

might also be worth modulating the light with a carrier and then synchronous rectification to recover the signal to remove any external interference.

fixed and tapered apertures around the light source and sensors may also help

bill
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on October 29, 2019, 07:28:56 PM
Bill, thanks for the suggestions. Could the differential approach be used for more than one pair, at the same time. Like for all the six outputs?
I'll have to admit, that it is grey area for me, even though there might be just simple math or logic involved.

But on the other hand, I have made a very simple square wave generator, to feed the IR leds, instead of DC. It is based on a 555-timer IC, that runs at ~120KHz.

That frequency is just a sum of the components, that I had on the shelf:
(http://www.elisanet.fi/kz1706/optical_pup/square_gen.png)
 
I have noticed, that by using plain DC for those leds, they tend to hog a lot of current, without actually "feeding" the receivers. I see those receivers, as bird cubs, that scream for food all the time.
When they are fed hundreds(or thousands) of times per second, they don't have the time to observe the environment, or make noise.

I'm not sure, if it is any form of modulation, but rather pulsing, to keep the receivers busy, so that they notice only the aberrations in the IR beams.
Also, current consumption is minimal, when compared to DC.

Some specs: my current setup has 3mm IR-leds (IR204), and 3mm IR-receivers (PT202B).







 
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: BillTodd on October 30, 2019, 06:31:39 PM
Your generator is effectively sampling the position of the string (like  strobe light) , it is sufficiently fast (at 120kHz) to catch all audible frequencies (has to be at least twice the maximum desired frequency or it will produce differential , alias, signals ). You may be able to reduce power consumption or reduce noise by reducing the on period while increasing the drive current (such that the average and peak current is within the diodes range). (look up shannon sampling theory)

An effective differential pickup would require at least one opamp per string (but they come four to a box so it's not such a problem).  The hardest bit is the optical layout , are you relying on reflection from the strings or trying to have the beam cut by it?.

I wonder if you could use a pair of standard opto switches at slightly different heights to catch the top and bottom (or left and right) of the string??

Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on October 30, 2019, 09:49:16 PM
Although the square wave generator pulses the IR-leds, which are now in series, there seems to be a lot of deviation between their output ranges.

At the very beginning, I tested those IR-leds in parallel configuration, just to find the same differences.   

So today I tested them with an adjustable DC source, still in series. All of them have different voltages, or "sweet spots", where they give the most output for the receivers.
Bit confusing, but I guess they(IR204's) weren't made to be that accurate, after all, what comes to the operating voltage and current.

One thing, that I might test with them, is to use potentiometers to "tune in" each led. If that doesn't work, it's just an end of part one, as I have already few other types of IR-leds on the shelf.

Bill, I took a look of the shannon sampling theory. Somehow it makes sense, but I haven't found yet a way, of how to implement it in practice.

I'm not quite sure yet about the optical layout. For example, Opik pickups by Light4Sound use reflective technique, which is one option.

Current setup focuses on disturbing of the IR-beam, instead of cutting it, as it could require microscopic precision.

Using the optoswitches is also one option. My local supplier has some Omron optical switches available, which I guess, could have better tolerances, than the discrete IR-components.



 
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: BillTodd on October 31, 2019, 05:15:52 AM
how are you measuring ir output? 

The ir laser in a cd pickup uses a second monitor diode to detect the laser level, that is fed back to the laser current to keep the laser output level constant with temperature , aging etc.

It seems more likely to me that the variance you are seeing is due to optical path differences.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on October 31, 2019, 06:54:33 PM
I think the IP-receivers' outputs could be measured with multimeter, but the readings come and go so fast, that it's a bit hard to follow. 

When plucking a guitar string, there is first the highest peak, then the signal slowly fades away, so it hasn't that much of constant values.

Without having a storage oscilloscope, I judge the results just by listening. That way it's easier to observe, if the signal is too weak, or is it too strong, causing distortion.
I have tested the IR receivers one at a time, and the signals from them goes first through the unity-gain op-amp(9V battery powered), then to the laptop's mic input.

Optical path differences, yes they likely have an effect. By using variable DC-supply(30V/3A), that displays both voltage and current, I got some results.
From left to right, E1 is the thickest string, while the other E is thinnest.

When using plain DC, the "window", where the leds gave any usable output was really narrow(numbers above the letters)
(http://www.elisanet.fi/kz1706/optical_pup/DC_results_.png)

One (or at least me) could expect more output, if more voltage is used. But no, outside of the above voltage ranges, there was no output at all.

I must be missing something essential here. Perhaps the receivers have something to do with those narrow windows? I Can't tell.

Then comes the test, using pulsed square wave at ~120KHz.
Generator schematic:
(http://www.elisanet.fi/kz1706/optical_pup/120KHz_sq_gen.png) 

As can be seen, there is 7812-regulator, meaning, that it provides regulated +12V voltage for the 555- timer IC.

Results are very confusing. Again, numbers above letters present voltages fed to the circuit, to find out the sweet spots of the IR-leds outputs:
(http://www.elisanet.fi/kz1706/optical_pup/120Khz_results.png)

For some reason, E1 has the broadest response, as it gives good output, when supplied from 11 to over 20 volts.

All the others have very narrow output ranges, that works only below the actual, regulated voltage(http://emoticons4u.com/crazy/1261.gif).





 
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: BillTodd on November 01, 2019, 12:49:35 PM
at a guess the larger string is obscuring the most light and allowing the transistor to operate in its linear ( non-saturated) region.

ATM you seem to have the string just wobbling  about infront of the transistor, you really need to get only the edge of the shadow to fall on the transistor die . Sketch out a scale diagram of light source , string and receivers , to  workout where the best placement for each should be. you may need to add apertures to source and receivers to get a crisp shadow.

You are making it hard for yourself if you don't have the right tools. Without an oscilloscope you are blind . You don't need anything expensive, the little pocket devices sold ln eBay would be more than good enough for your purposes.

BTW the 33u in the output that drives the leds , is making them see an ac drive . It is not necessary .
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: PekkaNF on November 01, 2019, 04:29:53 PM
To my experience pretty much all optocomponenets are pretty unlinear and they have large variance between componenets even in same manufacturing batch.

I would start checking iif all those optodiodes will need individual current or voltage source. If they are laser diodes, they normally have their own drivers and they behave very diiferently from normal LEDs. My point is that each emitter needs certain driver and you might need a separate driver for each channel.

Also receivers are most likely unlinear and strings/optical baths are diferent -> you need some processing for each channel. I can't estimate if with one opam you can bias, linearize and amplify signal. They must be tuned individually. No idea how to do that.....different frequences and plucking the string might not be exactly constant------probably to keep un plucking until statistically representatice smaple cloud has been reached.

Pekka
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on November 01, 2019, 08:04:59 PM
Bill, yes the string shadow, and the placement of the sender/receiver pairs needs more testing.

In fact, one of the commercial optical pickup uses aperture to "tighten" the width of the receiver's "eyesight": https://patents.google.com/patent/US20110265635   

Oscilloscope has been on my buying list for years. I have waited for the "justification" to purchase one. Perhaps the time to get one has come closer.

I breadboarded the 555- timer circuit, using a bit different configuration, that I found on the net. So now it gives DC pulses, instead of AC.
But the results are pretty much same. The leds still have their narrow, individual ranges, that produce output.

Pekka, it seems to be very true, that they have plenty of deviation. Actually, what I'm planning to do next, is to somehow feed each of the IR-leds separately, from the same voltage source.
Maybe at first by using separate trimmer pots for each one, to see, how it works.

 

Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on November 02, 2019, 09:08:27 PM
I tested the previously mentioned configuration, using trim pots for each sender/receiver pair. Yes, it kind of works, but the receivers' outputs are still at a very narrow ranges.

On those narrow output ranges, it's more like an on/off switch situation, where the outputs are either non-existent, or are overly strong, causing distortion and a lot of noise.

I don't mind the distortion, as all those outputs, when I finally get there, are to be converted to CMOS- level square wave form.

But with that much noise, it seems to be very difficult to achieve with the current mechanical setup:
(http://www.elisanet.fi/kz1706/optical_pup/separate_pickups_2.png)

As I see it, is that when the sender/receiver -components stare each other in the eyes at so close distance, the receiving one goes mad, and gives overly saturated output, even if it isn't amplified in any way.

After all, the optoswitches have similar configuration, but are perhaps designed to be nothing more, than on/off -devices.
---------------------------------------------------------------------------------------------------------

I'll put the current concept aside for now, and move on to the next mechanical configuration, which concentrates to the reflection of IR-beam from the vibrating string.

To be honest, I'm not going to re-invent the wheel. Instead I'll use the info from the previously mentioned patent.

As it is for commercial product, there obviously isn't any "specific" details available.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: BillTodd on November 03, 2019, 05:18:07 AM
The photo transistor is just like a normal transistor, its transfer characteristics are determined by base current. Even in a simple amp circuit the base current is carefully controlled , usually by a feedback mechanism (.
e.g. emitter resistor)  .  The photo tranny's base current is supplied indirectly by the impinging photons,( and it doesn't really care what colour they are)  there is no feed back , even with emitter resistors.

You have to either have to provide a very stable light level  (practically impossible given the circumstances ) or some means of feed back  to control the level.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: WeldingRod on November 06, 2019, 07:41:16 PM
You might be able to get a steady string motion signal by using a speaker near the string, or driving a conventional pickup with a function generator.

Sent from my SAMSUNG-SM-G891A using Tapatalk

Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on November 07, 2019, 03:29:40 PM
Bill, yes the phototransistors(at least the ones I have tested(PT202B)) seem to be quite tricky to work with, as they all have different, individual operating levels.

WeldingRod, that's a good idea. There is actually a commercial device called "E-bow", which allows the player to electromagnetically "excite" the strings, but only one at the time, to make the string to "sing" as long as the device is applied to it.

Hmm.. after a quick search, there seems to be a plenty of those who had done "diy" -versions of that device, so I guess it shouldn't be that hard to build.
That could be nearly ideal one to produce constant signal from the string(s), which could then be more easily measured as an output.

In the previous post, I mentioned that I'll be moving on to the reflective approach, as mentioned in the patent. But not so fast, as the saying goes.

While taking the current setup apart, which consist pairs of 3mm sender IR-leds(IR204), and 3mm receiving phototransistors(PT202B), I Somehow got to this crazy, 'mad modder' -mood, and tested, how the actual emitting IR-leds(IR204) react, when they are treated, as receivers.

To my surprise, they provide quite a lot of output, when considered them to be emitters. Also they are bit more forgiving, than the optotransistors, what comes to the operating levels.

So I tested a pair of IR204's, one being the sender, and the other being receiver. Didn't seem to work well with plain DC, so I switched to previously used, pulsed source.

Crude circuit, that I'm currently using to amplify the signal:
(http://www.elisanet.fi/kz1706/optical_pup/072_amp.png)

It is powered by split power supply. But so far, there is good output, although with some hum. But that is mostly due to the jungle of wires involved, when testing.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on November 09, 2019, 08:18:23 PM
After testing several kinds of circuits found on the net, considering sine wave(amplified output from the receiver) to square wave conversion, it doesn't seem to be that straightforward. 

One of them being a zero crossing detector, that, as I assumed, should be sensitive enough for the purpose:
(http://www.elisanet.fi/kz1706//optical_pup/ZeroCross1.png)

But there wasn't any output at all. So I removed all the parts from the breadboard, just in case, that there was mistakes, and built it again from the scratch. Still the same result.

Next thing was to test with multimeter, does the 'preamp' -circuit(mentioned in previous post) give measurable 'peaks', as the electromagnetic pickup does, when the string is plucked.

No, it didn't. Be it AC or DC range. Nothing. But the output is still there, when connected to the laptop's mic input. Somehow it sounds stronger, when compared to the 'high output', dual coil electromagnetic pickup.

If there isn't measurable AC or DC values, then what kind of output is it anyways?
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: russ57 on November 09, 2019, 11:34:17 PM
The first thing to check is the frequency range of the multi meter.
Secondly, the meter will measure the 'rms' value of the signal, this is the average value, not the peak. And it probably assumes a sine wave.
If your signal is a series of 'spikes' rather than a sine wave, then the rms value could be very low.
Audio design really needs an oscilloscope. You can pick one ok for audio off any Chinese trading site if not eBay for under aud50. £20?
(Turning a sine wave to square is easy. Just apply massive gain) .

Russ



Russ

Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on November 10, 2019, 08:14:11 PM
Russ, yes I've been searching for the oscilloscope for a while now. Maybe something like the Nano DSO series, with colour screen.
Some of them even have two channels, like SainSmart Mini ARM DSO202 Nano.

Most of them on the Ebay are located in China, which means that the delivery times tend to be rather long. So I'll probably pick one of the few ones located in Europe.

I'm tempted to go and buy a full size, entry level Rigol, which seems to be quite popular. But perhaps it's not a time for going that far yet.

What comes to my description of the signal of the plucked string, when measured from the electromagnetic pickup's output, it was incorrect.

It actually isn't in a form of spike(s), but more like an envelope.

I'll probably butcher the subject by trying to explain it, but the first picture on this page hopefully shows, what I mean by the envelope: http://www.muzique.com/lab/pick.htm
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: PekkaNF on November 11, 2019, 03:00:02 AM
I really would recomed entry level oscilloscope. Even old analog would be whole lot better than without one. I have had one old CRT 10MHz model that I bought 20€ and gave away, it would have been fine for this.

New DSO:s maybe easier to use, they normally can "find" the wave form with a push button. If you have nothing connected or no signal you normally find mains frequency or quantisizing noise.....but that is learning curve.

With low level audio signal you can't even blow up the scope, when you mess with grounds.....normal scopes have only one ground = chassis, this ir nice to acknowledge.

I had Rigol 1052 (old model several years, sold it with 250€), I think, New owner has been really happy with it. I bought Rigol DS2102E, somewhere bit over 600€ that time with serial decode etc. I wanted bigger display and some triggering options.

https://www.batronix.com/shop/oscilloscopes/DSO.html
https://www.batterfly.com/shop/

They offer few times a year free upgrades of software features, like triggering and decoders (if you are into serial protocols etc.)

Discrete devices with their own displays, settings and ergometrics are just so much nicer to use than the boxes that need a laptop and weird ground (trough the laptop?).

Pekka
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on November 11, 2019, 06:29:27 PM
This post is an off-topic, but sort of related, because it considers the recommended kind of measuring device, oscilloscope.

After pondering, and watching countless amount of Youtube review videos about oscilloscopes(mostly EEVblog's, and also reading his forum),
I came to the conclusion, that the desktop one could offer a lot more functions and options, than I could ever need or fully understand.

One thing, that I must say: This kind of project (optical pickup for the guitar) definitely does not require a fancy 'full-featured' desktop oscilloscope, for the experimenter to observe signals.

------------------------------------------------------------------------------------------------------------
Totally off-topic:

When I'm talking about having a desktop oscilloscope, it's more like a part of my own journey, as I have wanted to have one for years now.

Then came the question: which brands are available in finnish stores? Owon's cheapest model(SDS1022) has nice, big 7 inch screen in it, but for some reason, there isn't too many reviews to be found of that online, so the reputation isn't confirmed in any way.

After all, Rigol is the one, that I ordered. As Pekka said "..but that is learning curve". Probably a steep one, that holds true for me, when I get that device in my clumsy paws.
-----------------------------------------------------------------------------------------------------------------

Back to the original subject. As Russ mentioned, 'Turning a sine wave to square is easy. Just apply massive gain'. But how much gain can one apply to a single op-amp, without making it self-oscillating? Or is it something, that requires multiple stages?

Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: BillTodd on November 12, 2019, 04:22:16 AM
For analogue audio work a 20MHz bandwidth 'scope is plenty. You don't need serial format converters or logic analysis functions.

If you are going to blow serious money on a new one, then buy the best most highly featured one you can afford.

If you just want something to debug your pickup then buy something cheap and cheerful , it will always be useful even if you buy something better.

Beware of the youtube reviews, They don't spend their own money and, like Dave's review yesterday, will compare a 70 currency unit ($£€) device with one costing 12000.

Seek out other purchasers/users of the device on forums and ask their opinions.  BTW that little scope wasn't too bad, but I felt it was still too expensive , at 40 cu it would have been a good buy .(you have to be cautious about the results of any instruments when working near their limits)

If you don't already have one, get yourself a copy of 'the art of electronics' by Horowitz and Hill .  I think it will fill a few gaps in your knowledge.and is always useful as a reference.













Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on November 12, 2019, 07:06:04 PM
I tend to take Youtube reviews with a grain of salt.

Before purchasing something bigger, I have a habit to read different forums, as it's possible to get more unbiased, and wider picture, considering the brand(s), and possible problems/solutions involved.

The book you mentioned seems to have more approachable way(at least for me) to explain electronics. When looking at table of contents https://artofelectronics.net/the-book/table-of-contents/ (https://artofelectronics.net/the-book/table-of-contents/), there is some pretty interesting stuff. Thanks for suggestion.



 
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: WeldingRod on November 12, 2019, 07:24:58 PM
The Art of Electronics is a seriously great book, and I enjoyed reading it, um, many, years ago!

Sent from my SAMSUNG-SM-G891A using Tapatalk

Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on November 15, 2019, 07:54:32 PM
I think I found at least one reason, why the previously mentioned zero crossing detector didn't give any output, even when signal from the receiver was amplified.

The signal exists, but it seems to 'float' about 780mV above the zero volt point. Maybe not the most scientific way to measure that, but the result is there:
(http://www.elisanet.fi/kz1706/optical_pup/DS1Z_QuickPrint2.png)

Could the reason for the signal floating above(or below) zero be something like a voltage offset?

I have a very shady understanding about how logic level output can be treated with pull-up, or pull-down resistor, to bring the 0's and 1's to the acceptable 0 to 5 volt 'window'.

Does that apply to analog signals at all?

But questions aside. The square wave generator, that I used to feed the IR-led, or sender, was again based on the 555-timer -IC(I should probably have a screen shot of it's output too).
After all, the output is square wave, when compared to the receiver's one.

No matter how many different versions I've tried out, all of them suffer 'duty cycle vs frequency' dependencies. When one is changed, other changes also.

---------------------------------------------------------------------------------------------------------------------------------------------------------------------------
One might guess already, where this leads. Now, that I have a multimeter with a colour screen, I'm obliged to have a proper function generator (http://emoticons4u.com/crazy/1087.gif).

I have looked for something simple, like Velleman's HPG1MK2, which has 1MHz range. But after looking for it's specs, it doesn't seem to have any kind of duty cycle control for the square waves.

I'm aware, that Ebay offers a lot of 'authentic', old hardware, but I'm not so sure about them.

 



Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: Sea.dog on November 16, 2019, 06:43:13 AM
You may need an additional amplification stage before the signal is applied to the detector.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: PekkaNF on November 16, 2019, 08:20:41 AM
There is always a little buffereing and level adjustment on analog/digital signals. You may want to search logic level on TTL or mathever logic circuits you have. There are some differerences wetween different logic levels voltages and sourcing or output currents. Usually schmit

I have this very generic function generator and it does pretty much what it says. Cheap, not extremely accurate and not the best quality signal (some noise and such) and pretty close to 100% that I need on general simple signals. Only thing is that the buffer does really output great signal to 50 input at more than 5 MHZ or such. Should not be problem for your use.

https://www.ebay.com/itm/24Mhz-Dual-channel-DDS-Function-Arbitrary-Waveform-Signal-Generator-Sine-Square-/181775301443?hash=item2a52a6fb43:g:RxEAAOSw~ZdVfuQg

It does not have the skleekest user interface, but it is easy to use on all normal waveforms, dutu cycle, offset voltages and such basic functions you need. It is not that great on advanced waveforms, but that a little more advertising gimmic, if I ever need that I would buy completely different "box".

There are cheaper ones for square vave dutu cycle, but they are even harder to use effectively. Least the ones I have tried.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on November 17, 2019, 08:15:06 PM
Pekka yes I've been looking for different ways for analog to digital conversion. Well not exactly that, but more like simply chopping an analog signal wave to 0 to 5 volt square wave.

Thanks for suggesting the function generator. I checked the link, and that one, or similar should fit for the purpose.

Little bit of hands-on testing: I took one pair of sender/receiver out of the guitar, to see, how the signal(~50khz) transfers through them.

Pulsed output from the 555-based square wave generator:
(http://www.elisanet.fi/kz1706/optical_pup/555_output.png)

Then it goes from sender to receiver, whose output is fed to an op-amp like this:
(http://www.elisanet.fi/kz1706/optical_pup/072_dc_offset.png)

Resulting output, although not symmetrical, sits finally around the zero volt point:
(http://www.elisanet.fi/kz1706/optical_pup/opamp_output.png)

Now, that the signal crosses zero point, it is sent to a very simple zero cross detector, which requires only one resistor to be added, that I found from the LM393's(comparator IC) datasheet.
This version didn't work at all:
(http://www.elisanet.fi/kz1706/optical_pup/393_zero_cross_det.png)

This one gave at least some kind of output. Perhaps the right direction, but not quite there yet:
(http://www.elisanet.fi/kz1706/optical_pup/zcd_2.png)
(http://www.elisanet.fi/kz1706/optical_pup/zcd_output.png)

I always like to start with minimum part count, as on project like this, the number of parts are eventually multiplied by six(except the possible dual/quad IC's). But it is to be expected, that the zero crossing detector needs more parts to make it more useable.

I'm sure, that using the zero crossing detector is just one option, but as I have comparator IC's at hand, I'll give it a shot to see where it leads.

Plenty of testing ahead, as the visual results so far exclude the effects of actual, vibrating guitar string in the infrared beam.

 


Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on November 19, 2019, 06:41:58 PM
At first, I'll have to admit, that there was a gross mis-reading by me, of the values showed on scope. That dawned to me, when tracking down the reason, why I can't get that zero cross detector to work, as expected.

After digging on the net for alternative ways to amplify the signal from the receiver, I found out, that photodiodes and 'transimpedance' amplifiers go rather often hand-in-hand.

Without knowing much about it, or even having an actual transimpedance op-amp chip, I looked for the configuration.

Bit of testing with one half of the very basic TL062 op-amp:
(http://www.elisanet.fi/kz1706/optical_pup/photodiode_amp.png)

Output was fed to one of 'schmitt triggers', which is 1/4 of the 4093 IC, that I have at hand:
(http://www.elisanet.fi/kz1706/optical_pup/schmitt_trigger.png)

The inputs were simply tied together:
(http://www.elisanet.fi/kz1706/optical_pup/schmitt_trigger_config.png)

Yellow curve is from the op-amp output, while blue one is from the 4093 chip:
(http://www.elisanet.fi/kz1706/optical_pup/square_wave.png)

If all goes well, there could be a possibility to move on with the project.



Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on November 21, 2019, 06:31:33 PM
Not much to report, just some testings to confirm the previously noticed thing, that the photodiodes I have, seem to have a very narrow operating range, what comes to the light intensity of the sender(IR-led).

Applying more and more current for the sending ir-led doesn't help, although one could expect, that the receiving photodiode would take all the 'juice' gratefully, burp, and demand more.

But after all, there is at least one solution, that I noticed after testing: by using the transimpedance(ish) configuration:
(http://www.elisanet.fi/kz1706/optical_pup/photodiode_amp.png)

Replace the 1M resistor with 1M trimmer potentiometer. That way the narrow operating window of the photodiode can be altered to suit the following stage, which is schmitt trigger.


   
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on November 23, 2019, 06:36:11 PM
I did some testings to see, how the vibrating string affects the pulsed infrared beam between sender and receiver. Had to use the thickest string on the guitar for that, as the effect is quite subtle, when looked at the scope.

Here the string is plucked, and its vibration appears only at the trailing edge of the pulsed square wave:
(http://www.elisanet.fi/kz1706/optical_pup/string_signal.png)

The string signal seems to be more audible, than visible. It has some noise also, but not as much, as the earlier used phototransistors had.

I used again laptops mic input as an audio probe. It adds some 'weight' for the signal seen on the scope by altering it. Perhaps it could be better to use them separately, one at a time, to find out the best output ranges, either visibly or audibly.

The ~100kHz 'carrier' frequency should be sifted out at some stage, I guess. Though I'm not sure, what sort of modulation it has with plucked string signal.

After all, this projects' goal is not to produce a sweet, clean guitar tone. More like to squeeze the outputs to a form of a hex fuzz, that could possibly be used for a pitch tracking purposes also.


Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on November 24, 2019, 08:16:44 PM
I've been looking for a way to suppress the ~50Khz 'carrier' signal from the string's one, that modulates it. Resistor-capacitor low-pass filter could be one way, as there are calculators for that online.

Another way that comes to mind, could be to somehow extract only the difference between the higher carrier frequency, and again the lower one that modulates it.
But as they are already mixed together, it doesn't look that simple.

Simplified signal chain goes like this, where the red one represents the vibrating/modulating string:
(http://www.elisanet.fi/kz1706/optical_pup/signal_path.png)

The carrier square wave, when it goes through sender to receiver, has always more arbitrary form, which seems to be very sensitive to any and all kinds of adjustments.





 
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: PekkaNF on November 25, 2019, 07:02:32 AM
Few random thought....not sure if this is usefull...

1: Signal to noise ratio looks bad. Is it good enough? Any way to improve with electro-optical or mechanical construction.

2: Modulation...I lost the plot somewhere why this modulation is used? I think that if modulation is need ideal would be sine wave, because it has only one frequency. Square wave needs to be really high compared to information signal and still simple low pass filter will strugle.

3: Modulation/demodulation reminds me of AM-stuff I used to read and even experiment a little when I were a kid....like one transistor mixers:
https://www.engineersgarage.com/circuit_design/circuit-design-how-to-demodulate-am-signal/

4: Still on this demodulation. If you want to get rid of the IR-led carrier signal you have several options. Have you tried to add pick up signal and inverted signal to subtract the unwanted carrier signal out (that effectively should be very close to IR modulation signal) Is't it.

I haven't been fiddling with audio devices much, this "information" may not be relevant.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: BillTodd on November 25, 2019, 07:25:31 AM
I'm not sure why you want a square wave o/p (the fundamental frequency only will be a sign wave)  but..

one way is to synchronously sample the o/p with the illuminator's clock i.e. only test the level when the light is on (this should also improve s/n) but , you should really have a sample frequency (anti-alias) filter if you want to remove all sampling artefacts anyway.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: WeldingRod on November 25, 2019, 01:47:35 PM
I think the reason all your variation is on the trailing side is that you are triggering on the leading edge, which fixes that location on the screen.  If your scope will do it, try triggering on the led drive signal.

Electrically subtracting the led drive signal should be easy, and would take out the bulk of your modulation.

Sent from my SAMSUNG-SM-G891A using Tapatalk

Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on November 25, 2019, 07:53:38 PM
Pekka,
1: Yes, the noise level is quite high so far, when using the previously mentioned circuits. What comes to electro-optical components, I have a few different types of IR-receivers, which are not yet tested.

And the mechanical construction.. there is always room for improvement, one of the most important being the accurate height adjustment of the sender/receiver pairs. Likely by grub screws.
The current mechanical setup is too narrow for that, but it's just one of the first practising platforms.

2: I got the idea for the modulation from several sources on the net. It seems to be true, that by pulsing the leds, one can get a lot more 'power' out of them, when compared to using plain DC.
At first I thought: "more is better". But when used on a project like this, overly powerful output from the sender IR-led goes way above the receiver's range.

Also, when using something like 50-100KHz square wave for modulation, it attracts all kinds of noises, if not properly shielded. Those noises don't necessarily show on the scope, but they are audible.
As I'm on the testing phase, there are a lot of wires around to act as an antenna.

3: Thanks for the link. I'll check it out.

4: As I've looked info about demodulation, it seems to be a very complex subject. As I see it, to cancel out certain noises/frequencies, one should be able to provide exact, inverted copy of it/them.

Bill, I'm not sure either. When I got the resulting ~50Khz square wave output, the vibrating guitar string was able to modulate it, but with a lot of (audible)noise.

WeldingRod, I'll admit, there is options/settings on the scope, which I'm not familiar yet. I thought about subtracting/cancelling unwanted frequencies, but as mentioned above, it isn't necessarily an easy task to do.

Today, after reading these replies, I decided to test using plain DC for the sender IR-led. I tried it earlier, but it was just too easy to burn out the buggers. One way to see, if they are dead or alive, is to use camera. 

Now, that I'm aware(sort of), that the ultimate brightness is to be avoided, perhaps more delicate approach is justified.

Result: the sending IR-led was fed with mild ~3,5mA DC, and the output was strong, not so much on the scope, but audible. And this time there was no noticeable noise at all.
But it wasn't enough for the schmitt trigger. Needs probably more amplification to produce string's frequencies in a square wave form.

I'm led to believe, that audio measurements on the scope could be very tricky. Don't know why, but that seems to be the case.

For audio probe, instead of laptop, I now use a guitar multieffect device, as I guess it's designed to handle better the incoming signals, without adding strain, or loading them down(impedance?).
The device is used without any effects, so only dry input signal appears at the output.
 
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: picclock on November 26, 2019, 12:33:56 AM
It seems to me that the signal output you are getting relies on the reduced off axis response of the detector, rather than the deviation of the string.

A possible solution may be to use an aperture in front of a large area detector such that when the string moves the size of the shadow changes. A square or rhombic aperture aligned such that opposing corners are in line with the string, would have minimum light when the string was at rest but it would increase directly in proportion to the deviation.

Just a thought.

Good luck

Best Regards

picclock
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on November 27, 2019, 08:37:05 PM
Picclock, thanks for the suggestion. I'm not sure, how the string actually changes or modulates the IR-beam. But it produces somewhat responding signal from the receiver's output.

As I've noticed, the axis between sender and receivers should be on the same level with string, to get the most output. But that's just one way that seems to work.
Again, I'm not sure if the string is exactly at the same level with the IR-components axis in that case.

One way to get close to the 'sweet spot', where the output is highest, is to feed strong enough square wave to the sender, so that it can be seen at the receivers output.
Although not necessarily square wave anymore after that, but while adjusting the pickups height up and down, that wave changes also, as the sender/receiver pair passes the string.

What comes to using apertures, I haven't got that far yet. With current mechanical configuration, the space between strings is rather limiting, but we'll see.
-------------------------------------
Newbie alert:

I spent plenty of time today to find out the reason, why the recently working circuits didn't give any output anymore, after a good start.

Solutions:

- try different configurations
- if none of them work, check the continuity of the wires
- blame the non-existent quality of your breadboard
- start pulling hair out of your head
- never suspect the 9V batteries, that you are using on a project, that include current-hogs like IR-leds(http://emoticons4u.com/crazy/1261.gif).

After all that, I tested one of the circuits with regulated PSU, and voila, the output was there again(http://emoticons4u.com/crazy/296.gif).





     
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on November 30, 2019, 08:02:58 PM
After testing different photodiode(as receiver) configurations, the overall output still wasn't at the level, that I expected.

I guess it would need a lot of amplification to get it to the level, which could then be usable for cmos(0-5V) devices. I used single op-amp for that, and the output should have been multiplied hundreds of times, but that didn't happen, so there is much more in it, than just adding input and feedback resistors.

Same goes with zero crossing detector(for converting sine to square wave) circuit, whose sensitivity should have been 10mV pp.

I tend to see the circuits that I've found as universal building blocks. But no, if they work for a certain application, that certainly doesn't make them universal.

So I'm heading back to square one, using again phototransistors as receivers. Although noisier, at least they provide more output as they are, even without amplification.

 












Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on December 01, 2019, 07:39:36 PM
Again, I was looking ways to amplify the receivers output. Can't tell, why the op-amps didn't work for that purpose in any way :scratch:.

Anyways, I remember seeing this project, that uses an audio amplifier instead of op-amp: https://makezine.com/projects/infrared-string-bass/

After a bit of testing, the 386-based amplifier actually seems to provide a lot of output. I skipped the datasheet's x50 gain version, and went for the x200 one:
(http://www.elisanet.fi/kz1706/optical_pup/386_amp_2.png)

Not the most sophisticated way, but if it works, the project could go ahead, after weeks of stuck in the rut.

 

Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: PekkaNF on December 02, 2019, 03:06:09 AM
I haven't been experimenting with photo receiver diodes in ages, therefore my memory is sketchy. You probably said which diode you used and read the data sheet. In my youth the photo diodes (as a component, maybe nowadays they have integral circuitry) were actually very unlinear current sources. To make any use of their output you had to treat them as a unlinear current source. I always resorted to datasheet and application notes basic circuits and tested them.

Phototransistor and specially pair mounted on same housing was my favorite, usually they were manufactured for automotive or industrial use and their application notes were made very easy to follow.

None of the photocomponents are very linear and stable, but you are not making here very linear system and your aim is just to get good signal and ennough head-room for the signal to keep circuit reliable.

Most of the times operational amplifiers can be treated as a building blocks - as long as you keep in mind offsets, biases and output loading, for me they were whole lot to easier to use than transistors on linear region. At the begining I was drawing capacitors between every stage to isolate DC-path (we are talking here audio signal) but that wasn't completely problem free either....sometimes signal riding on DC-offset is a good thing, just need to keep it in check and zero it before feeding it out of the jack. Pretty soon I lost interest on audio circuits and went different way.

With signal generator and scope you can figure out fast what works and where the problem is.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on December 02, 2019, 08:30:32 PM
Pekka, yes the optical components seem to have a 'life of their own', or at least the very few ones that I have tested. Not really a one weekend project.

Optoswitches could be one option also. Although they are mostly too big to fit between the strings, it would be interesting to extract the actual, tiny optocomponents out of them.
I have a couple of optoswitches from disassembled printer, but haven't had a chance to look for them yet.

As long as the string modulated ir-light between sender and receiver creates usable output, it should be a good starting point.

The function generator, that I ordered, should arrive in two weeks.

In the meantime, testing goes on, and looks kind of promising so far.

Current setup on breadboard:
(http://www.elisanet.fi/kz1706/optical_pup/breadboard.png)

Circuits involved:
(http://www.elisanet.fi/kz1706/optical_pup/1st_stage.png)(http://www.elisanet.fi/kz1706/optical_pup/386_amp_3.png)(http://www.elisanet.fi/kz1706/optical_pup/sine_to_sq_4093.png)

At first, I tested with thickest string, and the output was good, but when testing with thinnest string with same settings, there wasn't output at all. I changed the voltage to the sender, and by decreasing it, the output was there.

So all of the senders need to be tuned separately, to suit the string thickness. As they are fed with dc, for that purpose, multiturn trimpots could be a safer option to avoid accidentally burning out the sending ir-leds.

To get rid of the jungle of breadboard wires, maybe the circuits above are worth of perfboarding.

Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: russ57 on December 03, 2019, 09:04:15 PM
This is a bowed instrument not picked, but

Shows how a string vibrates.

I'm thinking that unless you have a very small aperture, you will have great difficulty in detecting reliably different amplitudes.
You may need an array of detectors rather than a single one.

(and if the detector is a current source, thanks pekka, then you may need a load resistor across the op amp input. Start with say 10k....)

Russ

Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on December 04, 2019, 08:15:34 PM
Russ, thanks for posting the video. Never seen acoustic bass that big. I'll bet the windows, if there were any in same room, could have hard time to stay unbroken.

Yes, it's easier to see the string vibrations of the bass, as there is a lot more weight or mass in them, than the guitar strings have. But the pattern is always same, be it guitar, bass, violin or mandolin.

The nature of the optocomponents that I've used so far, for detecting string vibrations, is still mystery to me. From what I've been reading on the net/forums, they shouldn't be able to capture any changes in string.

But somehow in practice, they do. A lot of it has to do with mechanical and electrical setup. With only one sender/receiver pair for a string, it is possible to get the output from skinny 0,010" string.

As Russ suggested, array of detectors could make the string signal stronger. Haven't got that far yet, but all additional output is welcome, to squeeze the string signal into square wave.

Besides of that, there is also possibility to get a 'clean', undistorted output of the strings using photodiodes as receivers. Haven't explored too much of that, just an observation, while testing things.

The detector(phototransistor), being a current source with op-amp, I couldn't find working solution.

That's why I moved to an audio amplifier. If one doesn't provide, the next probably will.


   


Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: WeldingRod on December 07, 2019, 07:36:44 PM
I used an ir led detector pair decades ago to build a system to detect oscillations in a levitated water droplet.  I used linear amplification.  The gap between the two was a couple inches, and the droplets were 1-4 mm range.

If you added a lens to focus the beam near the string, and possibly a lens to collect the light into the detector you.could increase your signal.  However, that will add focus/position stuff too.

Sent from my SAMSUNG-SM-G891A using Tapatalk

Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on December 08, 2019, 05:24:41 PM
WeldingRod, thanks for suggestion. When thinking about using an op-amp for amplifying the receiver(photodiode/-transistor) signal, there seems to be a whole lot of different ones.

The ones that I have, are TL062, 072 and 082s. Maybe they aren't suitable for the purpose, or the configurations weren't right. But that isn't an excuse to blame all the op-amps.

To get bit of a break from electronics stuff, I did draw some sketches of the possible next mechanical setup:
(http://www.elisanet.fi/kz1706/optical_pup/possible_next_mech_setup.png)

Same with an idea for height adjustment for the individual sender/redeiver pairs, using M2 screws:
(http://www.elisanet.fi/kz1706/optical_pup/possible_next_mech_setup_2.png) 

Contacting elements could be made of the header on the left:
(http://www.elisanet.fi/kz1706/optical_pup/contacts.png)

It has room for ~3mm height adjustment, which I'm not sure is enough, though. The screw operated height adjustment seems to be plausible, as I have tested it with a few printed pieces.

To get ahead of myself, here is one possible newcomer. Left one is 3mm optotransistor for comparison:
(http://www.elisanet.fi/kz1706/optical_pup/optoswitch.png)

The one on the right side was carefully removed from the optoswitch housing, which unfortunately doesn't have any model number in it.

While in one piece, I tested it in the breadboard, and the output wasn't strictly on-off type. Even a hair caused deviations in the output waveform.

Those components (sender/receiver) seem to be identical in size. Being that small, when compared to 3mm ones, there should be a lot more room for placing them between the strings.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on December 11, 2019, 06:42:22 PM
After some testing with current electrical setup on the breadboard, it could be worth of building. The circuits are very simple, but when there are six of them, using perfboard, it is way too easy to make mistakes.

So I'm going to make the actual pcb(s). Bit of an extra work, but the resulting board should be a breeze to populate.

The only thing, that has changed since I made pcb's years ago, is the laser printer. Hopefully its ink has similar properties, as the previous printer.
As always, there is only one way to go where no man has gone before find out.

In the past, I used cheapo transfer method, where the pcb pattern was printed to gloss or semi-gloss magazine/ad paper, then transferred to the copper surface of the pcb.
Results weren't 100% perfect, but in most cases, that was more than enough.

Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on December 12, 2019, 06:07:46 PM
Making the pcb went just fine, but only after etching, I noticed that it was a mirrored version of the circuit(http://emoticons4u.com/crazy/1087.gif)

But that aside, the first pcb consists only the amplifier stage for the phototransistor, in hopes of keeping the overall construction 'modular':
(http://www.elisanet.fi/kz1706/optical_pup/amplifier.png) (http://www.elisanet.fi/kz1706/optical_pup/amplifier_pcb.png)

After testing, that the above pcb works as expected, the first candidate for the next 'module' is one, that consist of 4093 ic's, with schmitt trigger configuration.

What I mean by 'modular', is that the amplifier stage isn't permanently tied to any of the following whatever-stages, so if one doesn't work, take it out and replace it with something else.

Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on December 13, 2019, 09:02:13 PM
The first pcb is ready to go for testing. For me, the drilling is always the most thrilling part.
-----------------------------------------------
Babbling:

Thin carbide drills are usually very fragile, and are to be rotated at high speed. Not so in this case, as I used about 2800 rpm(max rpm of my mill) for the 1mm one.

As a precaution, the drill's vertical movement was minimised, so that it just penetrated the pcb.

One might ask: why not use hss drills instead, as they are dirt cheap, and more flexible?
Anyone, that have used hss drills for pcb's, knows, that after 50 holes they are as dull as it gets, and tear instead of cutting.

Although carbide drills cost a bit more, and are not to be used for hand-operated drilling(ask me how I know), they don't wear out easily.
Some kind of (lightweight will do) drill press is required, though.

Reason for this run out? If there are newcomers reading this thread, willing to make their own pcb's, hopefully they get more info to get over the learning curve involved, than I had in the past..
-----------------------------------------------------------------
But enough of that. Drilled pcb as it is:
(http://www.elisanet.fi/kz1706/optical_pup/drilled_amp_pcb.png)














Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on December 16, 2019, 06:53:05 PM
There was an error in the previous pcb, but it's now fixed:
(http://www.elisanet.fi/kz1706/optical_pup/amp_pcb_2.png)

It's just a bare bone circuit, which could be cropped even more, by replacing upper right 10u capacitor with a jumper, as I'm not sure if it's needed at all.

Although it's working as expected, it seems to need some kind of psu filtering thingamabob to suppress overall noise. I use a simple one like this, which could also be used as a split power supply.
It was used only to power the amplifier circuit, and not the power hungry ir-leds:
(http://www.elisanet.fi/kz1706/optical_pup/pwr_supply_thing.png)

So far the testings and adjustments were done by using scope, function generator, and multimeter. But they don't reveal all. The end result is still judged by aural testing.

Next stage after the amplifier could be a schmitt trigger, zero cross detector, or about anything, that is able to clip the output to suit cmos ic's.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on December 17, 2019, 08:03:24 PM
Simple zero cross detector(zcd) from datasheet..
(http://www.elisanet.fi/kz1706/optical_pup/zcd.png)

..and 4093-based schmitt trigger were compared as signal 'squarers'.

Zcd did work, but its sensitivity(or lack of it) made it to cut the signal from the plucked string too early. Another version, that has 10mV sensitivity, although having more parts involved, could still be an option to test. With that high sensitivity, noise could be a problem, though. 

Zcd with an adjustable/variable input sensitivity would be jolly good to have in this case. But when searching on the net information about it, such things doesn't seem to exist.

Then there was the 4093-based schmitt trigger, which did let the signal from the plucked string to 'squarify' bit longer, making it to look more 'natural' response.

Current circuit has (maybe)enough amplification for the receiving phototransistor. On a second thinnest string(0,33mm/0,013"), when plucked, the output goes to 9 volt(with 9V supply), and fades as the string vibration decreases.

So the circuit is pretty much same, as it was previously:
(http://www.elisanet.fi/kz1706/optical_pup/sch.png)
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on December 18, 2019, 07:20:25 PM
After looking at the datasheet of 4093 ic, by lowering its supply voltage, the input threshold lowers also.

At 9V it is ~ 1,8V, and at 5V ~ 0,9V. By adjusting the 50k pot, there is a very narrow spot, where the output appears. Lower supply voltage makes that spot even narrower.
Multiturn trimmer pot could be a better choice for that, as they aren't that costly nowadays.

So far, circuits with minimal parts count are used. As I mentioned earlier, this thread is useless without pictures, but even more so without audio clips.

The mechanical setup isn't up for that yet, and needs a lot of testing as well. By using the current (flimsy)setup, it should be possible to use a least two strings, to make some nice sounds audio output.

The form of output, that I expect, could be fuzz/buzz. If all goes well, there should be some form of cross-modulation, that one gets only by using hex-fuzz.



 
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: PekkaNF on December 19, 2019, 02:36:12 AM
.....By adjusting the 50k pot, there is a very narrow spot, where the output appears. Lower supply voltage makes that spot even narrower.
Multiturn trimmer pot could be a better choice for that, as they aren't that costly nowadays.
.....
Normally trimmers are used only on fine tuning and discrete resistors are used to bring the trimmer "on range". This is because trimmers are not that stable and adjustment is easier if the adjustment is not ruined if a fly sneezes across the room.

This is probably all familiar to you?
https://www.electronics-tutorials.ws/resistor/potentiometer.html

(https://www.electronics-tutorials.ws/wp-content/uploads/2018/05/resistor-pot5.gif)

After you find the sweet spot with that trimmer you can find min/max range that is likely to be usable and then calculate to measure the legs resistance and use that to find needed discrete resistors and new trim pot size.

Second thing is that schmitt triggers pretty generally require "reasonable" signal - i.e. they don't have amplification. That means that if your signal level is small you need to boost it before schmitt trigger. Amplifier also gives you possibility to bias signal if it has a DC-component that would drive that amplified signal into saturation. You have used a capacitor, but sometimes that is not without problems and you might need that signal DC-component later to actively control led current to stay in linear region.

 
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on December 19, 2019, 08:05:29 PM
Pekka, thanks for the link. Yes, using fixed value resistors is in the plan, although on the thinnest strings, which have less sustain than thicker ones, finding closest resistor values could be a bit tricky.

On a second thinnest string, when tested with 100k pot, at the sweet spot, it was removed from the circuit, and its values were measured, being close to 60k/40k, or 40k/60k.

The supply voltage was lowered to 5V, but before testing all the six circuits together, I can't tell, if it's the the final value.

Other than that, I drew some scetches, considering the mechanical setup. The electromagnetic humbucker pickup was remover from the guitar, to make more room.

One thing, that has bothered me about current mech setup, is that you have to drill holes through the guitar to make connections to the pcb. 
 
A small step in hopes to change that:
(http://www.elisanet.fi/kz1706/optical_pup/mech_setup_scetch.png)

In that pic, sender ir-leds' common ground legs are brought together with pcb trace. The 2-pin grey headers, where the leds are to be connected, should be identical size in length.
But as I have long ones(40 pin), they should be sawed off of that, and milled to size using depth jig.

There is ~4mm space below the headers, so small 1.6mm pcb should fit there. Not sure though, if there is enough room for all the traces for optical components, when using single-sided pcb.
But as always, I have to test it to find out, how far I can get.

I guess that there is an option to order custom made pcb's, but from what I've read, in this country, they would cost ~200€/piece. Or maybe I'm missing something.

But that aside, to provide more constant signal from the strings, while testing one by one the outputs, could be to use a motorised piano-hammer-like contraption instead of tickling the strings with fingers and toes for the purpose. That may well be the next side-project.


Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on December 20, 2019, 06:58:04 PM
First test with a pcb, that may end up to the pickup housing:
(http://www.elisanet.fi/kz1706/optical_pup/pcb.png)

Thinnest traces are 0,5mm wide, and it took quite a few times to get them to transfer without cracks:
(http://www.elisanet.fi/kz1706/optical_pup/pcb_test.png)

Of course, the continuity of every trace has to be tested, before cropping the pcb to its final size.

Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on December 21, 2019, 05:34:32 PM
Using parts of the header(mentioned earlier) to connect the optocomponents seems to be way too complex for this project.

I guess it could be done, but cutting 2-pin headers to the exact length would take huge amount of effort.
Reason for using parts of headers was to keep the led/phototransistor pair somehow 'aligned', when adjusting their vertical/height position.

On to the next version, which rely on using two hex-head screws as vertical 'rails'. The first printed version of that was too loose for the led/phototransistor combo to stay in place.

There is a discussion on the 3d-printer thread about snap-fitting printed parts together. That's where I got an idea for this:

(http://www.elisanet.fi/kz1706/optical_pup/again_new_consept.png)

At first, the red screws couldn't hold the green part in place, when they were adjusted.

Then came the snap-in thingy;
(http://www.elisanet.fi/kz1706/optical_pup/again_new_consept_2.png)

Screws were pushed into the green sender/receiver housing. It took some force, but once in place, the overall construction is surprisingly stiff. And for me, that was only the first test using snap-in fit.

As the green part(height) needs only a minor amount of movement to find the 'set-and-forget' -position, wearing the printed parts out shouldn't be problem. But time will tell.





 

Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on December 22, 2019, 07:11:21 PM
A new version of the pickup housing. Couldn't find any 'neat' way, that could be easily done, so why not go for quick and dirty. Well, maybe not so quick, but at least it's dirty.

The idea is loosely same as before, but this time, instead of using the drilled holes on the guitar to put the wires through, wires go through the hole on the side of the pickup housing.

The skeleton version of it:
(http://www.elisanet.fi/kz1706/optical_pup/skeleton_housing.png)

And with the parts:
(http://www.elisanet.fi/kz1706/optical_pup/skeleton_housing_with_parts.png)

I printed that out, and although bony, it has some rigidity in it. If that isn't rigid enough in practise, I just have to add some wall thickness.

That kind of 'open' construction means, that the optocomponents should stay tightly in place through all the wild wiring hassle.
With right tolerances, they could be pushed in place seemingly tight, but that isn't enough. The trick is to apply small drop of lacquer or paint to the neck of the led/phototransistor.

When it's then pushed in the place, and let dry overnight, it should be more than enough to keep the bugger in the place.

Quicker way, using super glue might seem tempting, but the fumes of it will ruin the hemispherical 'seeing' area of the component, as they are usually made of some sort of plastic.



   
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on December 24, 2019, 09:15:21 PM
First tests with a new mechanical setup:

(http://www.elisanet.fi/kz1706/optical_pup/testing_mech_setup.png)

Wires of two pickups in place. But that housing might get too crowded, when all the wires are stuffed there, especially when using a 3mm thick shielded cable for the receivers.
But that's what I have at the moment.

One shortcut could be to mod the housing, so that the wires would come out of the side of it, instead of only at the end, as it is now.

Now, that the two pickups are in place, I tested shortly the 'E' -labeled one, which is for the thickest string.

The screw-adjustment for the height seems to work, as expected.

10Khz square wave was then fed to the sender/ir-led, and to my surprise, there was... well, I don't exactly know what it is, but perhaps a reaction, when adjusting the pickup up or down.

When it was in one position, there were bumps between the square waves:

(http://www.elisanet.fi/kz1706/optical_pup/bumps.png)

After some height adjustment, the bumps were gradually gone. So the difference, of what the receiver/phototransistor 'sees', whether it's string shadow, or whatever involved factor, can be visualised using scope. During that, the string stood still, and wasn't plucked, or otherwise excited.

Obviously that effect is greatly reduced, when testing with thinnest strings, but should be visible, though.



 





Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on December 26, 2019, 08:37:53 PM
Now, that the amplifier pcb is almost finished, I got curious of how the optical pickup sounds like. I tested it only on the thickest string. I'm going to order four missing ic's, once the holidays are over:
(http://www.elisanet.fi/kz1706/optical_pup/amp_pcb.png)

Output from the 386 amp is certainly very strong, as it's used in x200 gain configuration. The output is distorted in rather ugly way, but that doesn't matter, when the signal is to be conditioned for the cmos devices.

So far, there are no gain adjustment pots. Maybe they could be fitted afterwards, don't know yet. If not, then it's just time for a new pcb.

But to test how the string actually sounds, I tuned the overall output down by lowering the sender/ir-led voltage to the point, where there wasn't distortion.

Yes, it is possible to get a 'clean' output of this setup. Although I wasn't too much interested about that, it might well change.

The sound of the E (thickest string) is very bassy, not in a muddy way, but like a real bass. Didn't even know, that guitar can produce such low frequencies, without octave-down -effects.

Not only that, but when I increased the voltage of sender/ir-led, the overall output was again very high, I noticed, that plucking the other strings(whose pickup wasn't connected),
the E string ringed, responding to some of their plucked note harmonics.






Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on December 28, 2019, 06:07:12 PM
This one might be boring one, but as it is essential for the project(or at least with current mechanical setup), I'll give it a go anyways.

It's about height adjustment of the pickups. Today I tested, how to get the pickup(sender ir-led/phototransistor pair) to the position, where the string is at the center of the ir-beam.
That could of course be done by listening the output, and guessing the sweet spot by ear.

But guessing games aside. To see, if I can find anything useful for the matter, I fed all kinds of signals to the ir-led, and looked the results on the scope, while moving thin, string-like wire across the ir-beam.

The pickup used for this test is separate one, but similar to the ones, that are attached to the guitar.

Method, which I mentioned earlier, that feeding square wave to the ir-led, and judging the result by the looks of receiver output, when moving an object across the ir-beam, doesn't seem to be reliable.

There are simply too many things to be adjusted, before one can see the results(if any).

While frustrated about turning all the knobs of scope and function generator, there was one thing, that I hadn't noticed before.

When I slowly moved thin(and thicker ones also) string across the ir-beam, the current readout of the psu went temporarily from 23 mA to a few mA lower, as the string was moved up and down.
(http://www.elisanet.fi/kz1706/optical_pup/psu.png)

After repeating that procedure few times, there was constant reaction of the current readings of the psu.

The circuit, that was used to amplify the phototransistor output, is same as in previous post.

The thing seems to be to feed that circuit through the ir-led, with a signal, that makes the receiver/phototransistor amplifier 'busy', while 'receiving'.

Even a small amount of deviation in the ir-beam seems to give the amp time to take a breath, so the current consumption decreases shortly.

In the end, I think that the deviations of current consumed by receivers amp could be more reliable way to measure the best position of the string, to get maximum output.



 


Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on December 30, 2019, 08:24:41 PM
While the current mechanical setup is in the guitar, and the amplifier pcb is fastened to the guitar also, I decided to have a look of another kind of mechanical/optical setup, which I tried very shortly in the beginning.

It was left aside, as I didn't have an amplifier circuit to provide enough boost back then. But now that I have, I thought that re-visiting that design could be interesting.

Don't mind the bigger setup, as the one, that I'm babbling about, is the small one on the upper side of the picture. It's glued in place:
(http://www.elisanet.fi/kz1706/optical_pup/another_test_setup.png)

The sender(ir-led), and phototransistor have 50 degrees angle between them. No any particular reason for that angle, other than to see, does the concept work:
(http://www.elisanet.fi/kz1706/optical_pup/optical_components.png)(http://www.elisanet.fi/kz1706/optical_pup/optical_components_test_housing.png)

That test housing has a "backrest" to keep the sender/receiver combo from rotating around, when adjusting the height. Seems to work quite well.

As can be seen on the first picture, that thing was tested on the thinnest string(~0,2mm). If that works, any string thicker than that should give even more usable output.

To my surprise, there was stronger output, than was expected, after adjusting the pickup closer to the string.

So far, I have only used the scope to see the results, but it's the resulting sound that counts after all. I haven't got that far yet, as projects like this tend to expand(explode) in form of countless possibilities involved.

But yes, I think the mentioned sort of setup could very well be more appealing to the most of experimenters, that are willing to get their feet wet.

Quick summary of the two lately tested concepts so far, but take it with pint of salt:

One with sender/receiver pair in opposite(horisontally) sides of the string:

+ immune to string bending(which is also a horisontal movement)
+ the "sweet spot"(max. output) could perhaps be found by measuring the current consumption of the amplifier circuit 
+ overall output level

- not a very practical to use, as the sender/receiver pairs (and their housings) protrude above the strings, so it's not possible to dampen the strings in natural palm-assisted way.
 
Then the one, that relies on reflecting the ir-beam from the string surface from the below:

+ remains under the strings
+ allows free playing, and string dampening at will

- rather sensitive to string bending(maybe not so, if multiple pairs of sender/receivers were used)
- can't think of reliable way to judge the "sweet spot" yet

But as always, all that needs a lot of testing.

To expand the subject even more, I'm thinking of ordering some hall-sensors, to see, if they could be abused used for this purpose. But that's beyond of this thread, though.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on December 31, 2019, 09:01:21 PM
Continuation for the previous post; I tested that configuration, where the sender/receiver pair was perpendicular to the string.

Results were quite disappointing, as there was a lot of noise, although the ir-led was fed with dc. Also the pickup should have been very(too) close to the string, to get usable output.
So far, that configuration is done and dusted.

Variation of that is kind of similar, but this time the sender/receiver pair was set to be parallel with string:
(http://www.elisanet.fi/kz1706/optical_pup/again_new_setup.png)

Output was bit better, with less noise. Also in that configuration, if the pickup was too close to the string, output decreased. I guess, that the reflection of the ir-beam from the string could be better also.

But the form of the output signal seems strange, as the waves are formed from tiny spikes:
(http://www.elisanet.fi/kz1706/optical_pup/output_signal.png)(http://www.elisanet.fi/kz1706/optical_pup/spikes.png)

Maybe the schmitt trigger could translate those spikes to more solid, rectangular shape. Haven't made a pcb for that yet, though.

So far, I have found one major drawback in that concept; the output signal changes, when the ir-beam is reflected from players hand, near the strings.

One commercial manufacturer uses the latter concept, but there the optical components have a lot more distance, apertures, and fancy ir-filters between them.
I'm not going to copy that thing, as it was never advertised to have properties, that I'm after. Perhaps slightly adopt the ideas, if needed.

But the general principals are there for testing purposes, after all.


 

Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on January 02, 2020, 08:25:34 PM
One basic testing version of the 6 x schmitt trigger board:

(http://www.elisanet.fi/kz1706/optical_pup/schmitt_trigger_circuit.png)

For some reason, I insisted on making as small as possible board. Then I had to cram the capacitors in(http://emoticons4u.com/crazy/1261.gif):

(http://www.elisanet.fi/kz1706/optical_pup/schmitt_trigger_test_pcb.png)

It lacks only two caps, which I'm going to order, besides other components. But when testing it with function generator and scope, it worked as expected so far.

All those clumsy jumper wires, I wish I could replace them by using two-sided pcb. That's a subject, which I haven't explored at all, as aligning the two pcb transfers with each other seems overwhelming, to get usable pcb. Maybe that's one tough side project for the future... 

Another version could be a bit simpler, with similar layout, using 40106 hex inverter gate, which has the needed six schmitt trigger inputs/outputs in one ic:
(http://www.elisanet.fi/kz1706/optical_pup/40106_pinout.png)

I'm not sure if that 40106 works as 4093's, that I have used, but maybe I'll order some, to find it out.
 
 
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: PekkaNF on January 03, 2020, 05:21:44 AM
.....
All those clumsy jumper wires, I wish I could replace them by using two-sided pcb. That's a subject, which I haven't explored at all, as aligning the two pcb transfers with each other seems overwhelming, to get usable pcb. Maybe that's one tough side project for the future... 
......

Not sure how you make the boards, but could you use the same method with transerfer sheets than is used with UV-method? That is to tape the transfer sheets facing each others into an "envelope" I.E. index them firs to each others and then slide the PCB blank in and then tape it into correct place.

Or you could use something to allingn the PCB into a "pocket" like this:
https://justaddelectrons.com/blogi/double-sided-pcbs-aligning-the-sides-for-exposure/

Or just drill holes on opposie corners of the PCB that has a mating parts on masks and then tape the mask (or in your case transfer) which has the same indexing holes.  Hell....you might even 3D print an alligment fixture for mass production:)
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on January 03, 2020, 08:02:46 PM
Pekka, thanks for the info. I was thinking of that envelope method, but the paper, where the transfers are printed, should be plain, instead of the magazine paper that has either text or images in it.

Glossy photopaper for laser printer could be a better candidate for that. Or some pcb-transfer specific product.

By using the uv-method, as the link provided tells, making two-sided pcb's could be a lot easier. Haven't got that far yet, when making pcb's. So indeed it would make a lengthy sideproject.

To get back to the project, yet another variation of the recent setup appeared. Previous one used 50 degrees angle between sender/receiver, to reflect the ir-beam from the string.
Output was there, but it was somewhat rather lacking.

Then I got a plan 9 from outer phase, for increasing the angle, and distance between optical components. That way, the sender(ir-led) could shine its light to a longer amount of string, meaning more string surface to reflect, and hopefully more output.

Now the angle between sender/receiver pair is 90 degrees:
(http://www.elisanet.fi/kz1706/optical_pup/90_degree_setup.png)

I printed a new housing, which should be a bit more 'universal', if the distance/angle between optical components needed to be increased even further:
(http://www.elisanet.fi/kz1706/optical_pup/and_again_another_setup.png)

Result is more responsive, and more 'solid' looking output, than the one with 50 degree setup. The sender is again fed with dc:
(http://www.elisanet.fi/kz1706/optical_pup/90_degree_setup_output.png)

Although I'm looking for hard-clipping, maximum output, there is also a great potential for experimenters, who are possibly looking for a clean output from optical pickup.
Just tune things down enough to get to that territory. In that case, using photodiode instead of phototransistor could be a better one, as it has lower output.

After all, these things always require testing, to find the options, that suit.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: JohnHaine on January 05, 2020, 06:57:31 AM
Interesting thread, haven't had a chance to read it all, but do you not have one problem with the configurations you are using?  Essentially the string when it is stationary obstructs the beam, so there is no output from the photodetector.  When the string moves, the output increases whether the string moves one way of the other.  So it will double the frequency of the vibration, and be veru distorted.  When plucked, the string moves essentially side to side doesn't it?  So to pick that up you need an LED shining down on the string and two phototransistors below it, equally illuminated when the string is centralised, while being differentially illuminated when it is moving.  Actually then you could use just a single LED and a "light guide" to distribute its light to each string, or one of those multi-LED strips, possibly with a diffuser above it.

Also in some of the early posts you seem to have a strange hybrid of constant current and constant voltage drive to each LED - really you want constant current so that each LED gets enough forward volts to work.  You could use a significantly higher voltage and a bigger resistance, or better use an inductor as a "dropper" using your chopper, with a buck diode to allow the current to flywheel when you switch the voltage off - this would be much more efficient, and the light output would be constant rather than "sampling" the string.

I hope these comments are useful, and apologies if I am covering old ground.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on January 05, 2020, 08:09:43 PM
John, thanks for the reply. Yes, there has been plenty of problems with the previous setups. Current mechanical/electrical setups aren't hassle-free either, and are more like testbeds for different concepts.

I guess, that when the string stands still in the ir-beam, only its shadow is detected, but as it has no motion, the receiver has nothing to generate. Perhaps a bit like a motion detector.

Movement of the string, at the very time, when it's plucked, could be seen as a very slow movement, as the plectrum/finger 'drags' it, and releases.
After that, when looking the string at the end, it moves like a jump rope(in exaggerated way).

I have thought of using a 'common' or single light source(consisting multiple ir-leds) for all the strings, but there is one thing, that I have noticed. The string thickness seems to have an effect, when adjusting the sender/receiver pair for the maximum output.

Also, if the receiver gets too much light from the sender, it goes 'blind'(maybe saturated), and doesn't respond anymore. That's what I have observed, while testing different mechanical setups so far.
Meaning, that if one setting works for one string, it needs to be altered for the other to fit.

That considers only the setups, that I've tested so far, which use single receiver/sender -pairs.

I wish I could explain all that better, but many things appear, when using components for the purposes, which they aren't designed for.

And, no need for apologies. Constructive input is always welcome.

-------------------------------------

What comes to the project, again another mechanical setup, where the sender/receiver pair distance is ~15mm, and the angle between them is 120 degrees:
(http://www.elisanet.fi/kz1706/optical_pup/120_deg_setup.png)

I already tested it on the thinnest string, and the output was there, not necessarily better than on the previous, 90-degree configuration, but I just had to choose one of the setups, to move on with the project.




Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on January 07, 2020, 09:46:40 PM
Three pickups in place for the first audio test. Another three 386 amp ic's are still missing:

(http://www.elisanet.fi/kz1706/optical_pup/first_audio_test_setup.png)

Again, that kind of mechanical setup's pickup outputs get easily disturbed, when moving hand over them.
They probably have their uses, but the strings should be plucked near the neck to avoid that.

One commercial maker uses 'strings-through-the-bridge' configuration for their guitars and basses, which doesn't have that problem.

Earlier I tested somewhat similar concept(where the sender/receiver "stare each other in the eyes"), although it had a bit different approach. I might get back to that, after all.

Results of the current setup: what comes to the 386-amplifier circuit, I wanted all the gain and boost it could ever offer. Now, that I have it, when listening to the output, it's overly raw, and very tricky to control in any way, as I left the gain pot out of it. It produces all kinds of farty sounds on its own, and isn't too responsive anymore.

In this case that amp clips very hard at x200 gain, which could be helped to some extent by increasing its supply voltage to get more 'headroom', but I'm not looking forward for that option.

So, as the mechanical setup will change, also the amplifier circuit has to be modified.

For the audio test, I didn't even bother to use schmitt triggers, as the output is beyond erratic already.

But all that aside, there is a hint of the effect, that I'm after, in the recorded masterpiece clip, in form of harmonies, which was made using the current setup:
http://www.elisanet.fi/kz1706/optical_pup/first_audio_test_.mp3 (http://www.elisanet.fi/kz1706/optical_pup/first_audio_test_.mp3)
 


   

 
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on January 08, 2020, 09:04:10 PM
I tested if the gain pots could be added to the current amp circuit, to make it more usable. It wasn't that hard, only one trace had to be cut and three holes drilled per amp. 0,8 mm solid wire was used for that, to make it stand straight, when adjusting:

(http://www.elisanet.fi/kz1706/optical_pup/gain_pots_added.png)

At first, I tried it with only one amp on the left side, and it makes a huge difference, and gives possibility to tame it down. But even after that, the output isn't exactly 'crystal clean', as it has some 'grit' in it.

The overall sound, when tested on the thickest string, is quite dark(as it was before, when testing with thinner strings).
Meaning, that the lower frequencies are certainly there, but the 'definition' is missing.

Not sure, if it's just a nature of the optical components, or the amp circuit itself. 

But here we go, instead of trying to get the maximum output, I'm getting interested of how the thing actually sounds.


   
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: AdeV on January 09, 2020, 03:26:16 AM
Pekka, thanks for the info. I was thinking of that envelope method, but the paper, where the transfers are printed, should be plain, instead of the magazine paper that has either text or images in it.

Glossy photopaper for laser printer could be a better candidate for that. Or some pcb-transfer specific product.

By using the uv-method, as the link provided tells, making two-sided pcb's could be a lot easier. Haven't got that far yet, when making pcb's. So indeed it would make a lengthy sideproject.

I did quite a bit of messing about trying to make my own PCBs last year.... I can summarise my results here (I'll do a proper write up someday):

1) UV exposure method is a right pain in the backside in a home shop. Getting the timings *just so*, and the exposure chemical strength *just so*, and then etching it just right - there are a LOT of variables. I reckon I must have used about 5 sheets of 100x160mm board, just to get one working 10x25mm board. And even that wasn't perfect.

2) Laser printer method is WAY easier. Forget the magazine paper, the laser printer will crinkle it, and it's hard to see the PCB print over the magazine print, especially if you're trying to go double-sided. Instead, use Vinyl (the sign-maker's type, that you cut in a machine). Works beautifully. I successfully transferred prints using a hot clothes iron, and latterly a slightly modded cheap laminator.

The only downside to laser transfer is pinholes - the laser doesn't cover 100% perfectly, so you can get pinholes in the traces. Not a big issue unless you've got very narrow traces. The upside is you just dunk the board straight into the acid after it's come out of the laminator. Have some acetone handy to wash away the toner once you're done.

Drilling PCBs is a whole different bag of fish. I bought one of those X-Y engravers, which works fine IF you get the boad perfectly lined up. Still working on that one... (well, will be, once I've got some spare time again).

Anyway - enough on that. I know it goes against the spirit of MadModder, but I think if I ever want a PCB that I *know* is going to work properly, I'll probably outsource it next time. PCBWay seems to get good reviews, and is cheap enough.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: PekkaNF on January 09, 2020, 05:07:16 AM
UV-method does needs some "dial" in. At the school we had repro camereras/films/pen plotters and all the works. Worked out fine. Secret was to use only fresh factory coated PCB:s and use two layers of film/paper that had darkest lines you could get and greatest UV pass trough you could get. Also the "envelope" had to be absolutely flat and UV-tubes have serious power.

I tried direct transfer method and I had best success with high coated high gloss paper, but applying just Goldilocks pressure/time/temperature turned out pretty difficult.

I have had some hit and miss success with UV-method, but my last try ended up to desperation, mainly because I had trouble with transparent material that would allow UV to pass. I bought the material that was confirmed to pass near 97% of that wave length....but I got the "improved batch" that was filtering about 99% of UV. Found out that when I made the "gradient" to find out, took like three minutes instead of usual 15 sec.

I have been thinking of routing method, but there is much CAM, indexing and all sorts of intricacies in that too.....

And then there is chemical copper and vias....

Probably best to buy board, but there is a definate apeal on "roll your own" .
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on January 09, 2020, 07:50:48 PM
Ade and Pekka, thanks for the replies. Yes, when using the laser printer for the transfers, there seems to be almost always some fine pitting/holes on the traces. But as they are quite randomly distributed across the traces, they should in most cases still be usable.

To avoid, or prevent the pitting/holes on the traces, there might be one (although unsolved) resolution for that:
After the transfer is transferred to the shiny copper surface, the traces with tiny holes and pittings should be "impregnated" with some (so far)unknown substance.

What I mean by that, is that the transferred traces with tiny holes/pittings are like an exaggerated sponges.
To fill all the holes and pittings, likely some stuff in liquid form, that is able to be sucked in to all those tiny cavities, while not sticking to the smooth copper surface, could be used, and let cure, before etching.

What that stuff could be, so far I have no idea. Not sure, if all that makes sense at all, maybe it was just a brain hickup.

But in the mean time, I tested one more thing with the current mechanical setup. This time the output is from the schmitt triggers. Some equalisation to brighten the sound, and a hint of reverb was added:
http://www.elisanet.fi/kz1706/optical_pup/schmitt_trigger_test_.mp3 (http://www.elisanet.fi/kz1706/optical_pup/schmitt_trigger_test_.mp3)

Those 4093-based schmitt triggers seem to work really well, cutting all the noises out. Major problem is the mechanical setup(as it relies on the reflection from the strings), which requires the ir-leds to be driven hard enough to make the trim pots quite warm.

For now, I'll put that mech setup aside, and get back to the earlier one, to see how it compares.

Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on January 12, 2020, 03:48:56 PM
When that previous mech setup was in the guitar, at the time I didn't think of the thing, that could extend its usability. But now it seems obvious: simply add reflective cover above the strings, that could be easily removed at will, to allow 'normal' access to the strings like this:
(http://www.elisanet.fi/kz1706/optical_pup/previous_120_deg_setup.png)(http://www.elisanet.fi/kz1706/optical_pup/reflective_surface.png)

It should eliminate the effect of the waving hand above the pickups. Also, while testing that setup, there was momentary, audible peaks on the output, when the plucking hand was resting over the pickups.

Again another factor, which I didn't consider, while consentrating on other things with that setup. But when thinking of it, if there was a smooth, reflective surface above the string, it could add more reflections from that very string, and somehow improve the overall infrared 'flux' from the sender to the receiver, in form of increased output with lesser amperage used by ir-leds.

All that is just an assumption so far, but it seems that I have to revisit that setup to find out.

That setup uses 120 degrees between the sender/receiver, making it bit too wide/large. The narrower 90-degree setup could have similar output. But as always, plenty of testings ahead.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: philf on January 12, 2020, 04:22:54 PM
......... But when thinking of it, if there was a smooth, reflective surface above the string, it could add more reflections from that very string, and somehow improve the overall infrared 'flux' from the sender to the receiver, in form of increased output with lesser amperage used by ir-leds. ..........

sorveltaja,

If you're going to try this wouldn't it be better to include a dividing wall between each string to prevent (or at least reduce any crosstalk)?

Phil
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on January 13, 2020, 03:51:53 PM
Phil, that's a very good point. After a bit of sketching, the 90 degree setup, and then same with a cover:

(http://www.elisanet.fi/kz1706/optical_pup/90deg_setup.png)(http://www.elisanet.fi/kz1706/optical_pup/cover.png)

I added 'legs' to one side, which rest on the base, so that the cover doesn't flex when the plucking hand rests on it. I might add legs to the other side as well.

Although on the picture, the surfaces, that face the strings, are a little bit curved, they probably should be flat, to get straighter reflections.
Do the flat, reflective surfaces still need some kind of fine adjustment option for alignment, can't tell yet.

What comes to the reflective surfaces, I guess they should ideally be mirrors. But that is really difficult to achieve, unless one has a very good skill in glass cutting/forming.
Instead of that, well polished, flat metal surfaces could do the trick. Maybe even shiny enough paint, or aluminum foil.

On the other hand, infrared light could have other reflecting properties, that may not be so obvious, when compared to the visible light. Haven't go into that too much yet, but the output differences should be measurable, when testing materials for reflection with ir-led/phototransistor(or photodiode) -pair. I'm looking forward to test it.

But before that, I have the older kind of mech setup in the guitar, so I'll test, how it works. Today I got the ordered missing ic's for the amp circuit, and if all goes well, it should be possible to test, how all the six strings sound together.

For 'mixing' the string outputs together, I simply used 'passive' one with 10k resistors for each output, when recording the previous audio clip. Schmitt triggers were used, and as their output levels are equally 'loud', not really need for adjustment between the outputs. Basically It's like three(later six) independent square -or rectangle wave oscillators.. well, oscillating together.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on January 14, 2020, 09:45:18 PM
After thinking of testing the rest of the older setup, mentioned in previous post, which was similar to this:

(http://www.elisanet.fi/kz1706/optical_pup/older_setup.png)

-- I already know, that it should work to some extent so far, and is something to get back to, if other mech/optical configurations fail.

I got curious, of how the reflections could possibly improve the infrared 'flux' of the 90 degrees -kind of setups, which otherwise require the senders(ir-leds) to be driven at higher amperage, to get usable output, if relying only for the reflections from the string.

So I sketched a simple setup to test, how different materials reflect that ir-light. It has a 5 x 10 mm 'window', where to put different materials. That setup is on the table, instead of guitar:

(http://www.elisanet.fi/kz1706/optical_pup/reflection_test_setup.png)(http://www.elisanet.fi/kz1706/optical_pup/reflection_test_setup_printed.png)

As a reference, I use a special, 8mm wide mirror from the old scanner. What makes it 'special', is that on the other side it is like normal one, that has a glass between the reflecting surface, and looker.
On the other side, no glass, only dead flat mirror surface. I tried to take pictures of it, but the camera sees it as a black/dark object.

But, after all, that kind of mirror isn't required/needed for the testing. Plain shiny aluminum foil gave about the same results, when the sender was fed with 400Hz square wave.

That was after rather quick testing, but the infrared 'flux' could be improved that way.

How all that stands, when that setup is in the guitar, with the actual vibrating string added to the ir-beam, I can't tell until more testing.   





Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on January 16, 2020, 08:59:43 PM
The new 90 degree mech/optical setup is ready for testing, for the thinnest string(0,25mm). For the reflective material, I glued aluminum foil to thin cardboard, so that it's easier to handle, and to cut to suitable size.
 
Then it was tested with the previously mentioned test-setup. Again, the input ---> output -results were close to mirror-like surface. But when looking that aluminum foil, it doesn't seem that 'mirrorish', though.

It could be carefully polished, but I'm thinking of replacing it with thicker brass, or aluminum, which should be a lot easier to polish, although they should be sawed and filed to the size.
Bit of work, but not a big deal.

(http://www.elisanet.fi/kz1706/optical_pup/aluminum_foil.png)

The cover with alu foil glued in. There were thinner legs on the front side, but I managed to snap couple of them out, while sanding the upper surface(it was printed upside down).
But the overall construction feels rigid enough without them, so I snipped rest of them away also:

(http://www.elisanet.fi/kz1706/optical_pup/cover_with_alu_foil.png)

I certainly hope, that this setup, even with cover in place, works, as it feels somehow very 'natural', without the feeling, that something is protruding between the strings:

(http://www.elisanet.fi/kz1706/optical_pup/cover_in_place.png)


After some testing with the thinnest string(without schmitt trigger), there was output, but it wasn't easy to locate the factors involved(as I have a nasty habit of starting at the hardest point available (http://emoticons4u.com/crazy/1261.gif)).

But after all, it looks promising enough for this setup; so the next step will be the thickest string, that has a lot more output to boot, to hopefully get a bigger picture, of how that setup works. 





 
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on January 18, 2020, 08:40:54 PM
The cover is now ready for testing all the strings:

(http://www.elisanet.fi/kz1706/optical_pup/cover_ready_to_go.png)

Aluminum foil was replaced with 0,25mm brass. The brass sheet was first treated with dremel and polishing compound, and after that, the pieces were sawed with a fret saw to size.
Bit of filing to remove any burrs, and that's it.

There is one thing though, when handling polished brass like that. To avoid any fingerprints on that shiny surface, straight after polishing, I covered it with a tape.
After sawing and filing, it was peeled off, before gluing the pieces in place.

Although the brass surfaces on the above picture might look like mirrors, they are actually quite 'shady'. But, after all, if aluminum foil performs well enough, polished, more solid metal surface should do even better. So fortunately, no need to go crazy with the polishing.

With this mech/optical setup, there are a lot of options to test. One being like this, where the distance, and angle between sender/receiver could be altered, while still using that very same 'base platform':

(http://www.elisanet.fi/kz1706/optical_pup/mech_setup_options.png)

At this point, when the amplifier circuit is completed(although not perfect, but good enough for now), as well as the schmitt trigger one, a very basic kind of 'foundation' finally exists.

With that in mind, it allows one to dive more into other factors of testing, like producing a stable signal from the string(s), that could be a lot more easier to measure, than simply plucking the strings.

One of the reader mentioned earlier something, that reminded me of a 'sustainer', that is used to input the string(s) signals, and fed back to the speaker-like 'exciter'(under the strings), to make them 'sustain', or ring constantly.

I'm considering of making that kind of sustainer for a single string use, that could be fed with open string's fundamental frequency with a function generator.

One heck of a side project, but the concept isn't actually new for me.




Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on January 19, 2020, 05:42:32 PM
It seems, that the 'resonator' to make the string(s) constantly ringing, while adjusting/measuring output of the pickups, doesn't need to be that complicated, as I expected.

Using small 8ohm speaker and function generator, I tested, what could be the position, to get the strings to respond to speaker signal.

So far, at end of the neck, where the guitar's headstock usually is, turned out to be the best location. My guitar is a decapitated version, so it doesn't have a headstock, but I managed to tape the speaker so, that it doesn't touch the strings:

(http://www.elisanet.fi/kz1706/optical_pup/cheapo_resonator.png)

That way the speaker makes the neck and body resonating, and therefore, also the strings. I guess, that it would help to have a headstock, with a mass in it to make the neck resonate even more.
Even that small speaker works, although a bit bigger one could help with higher frequencies, that the thinnest strings use.

I have another small 8 ohm speaker, and maybe I'll add it in series or parallel with the one already in use, to hopefully get some extra resonating power.

As one could expect, thicker strings resonate/vibrate a lot easier, than the thinner ones, which require the speaker(s) to be driven harder.

I'm not sure, if driving the speaker(s) straight from the function generator is a wise thing to do, for a long time period. To play it safe, I'm going to breadboard one of the 386- based amps to drive them:

(http://www.elisanet.fi/kz1706/optical_pup/speaker_driver.png)

Some things, of how to get the strings to respond to the fed signal: the signal itself should be in sine wave -form, as the wooden parts of the guitar do not seem to respond to (somewhat unnatural) square/rectangular waves that well.

Also, the signal feeding the speaker(s) should be 'tuned' for each string's fundamental frequency, to get them to resonate. That is, when testing one string at a time.

Although the setup is fairly simple, a sine wave generator, that has an option for fine tuning for the frequency, is highly recommended.



 


 
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on January 20, 2020, 08:56:38 PM
I tested the x200 gain configuration of the 386-amp, to drive the speaker, and it clips and distorts the fed sine wave, even at very low levels, making it useless for the purpose.
So next is going to be the mildest, x20 version.

I have also looked a way to improve the way, of how the vibration is transferred to the guitar body. There is a thing called 'vibrating speaker', which could be made using a sacrificial speaker.
As I have one, that's what I did:

(http://www.elisanet.fi/kz1706/optical_pup/improved_resonator.png)

I did cut the cone on the edges, and hot-glued random, printed left-over t-piece to the center of it. As the piece, that holds the strings, is made of aluminum, I used superglue to attach the assembly to it. Removal is easy, just knock it out.

It works bit better now. I have only three thickest string's pickups in the guitar so far(need to prepare rest of them also), but for them, the signal is more than enough. One of those strings, when tuned in, actually starts to buzz like sitar string, and the signal, that is fed, must be turned down, to get cleaner output. All that by abusing using only the function generator to feed the speaker.

As always, plenty of testings ahead, before usable end-results.
 
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on January 22, 2020, 07:34:26 PM
Some observations, while testing. First the overall base setup for all the strings:

(http://www.elisanet.fi/kz1706/optical_pup/test_setup_for_all_the-strings.png)

To avoid confusion about the guitar strings(with a standard tuning), they go from thickest to thinnest; e-a-d-g-b-e. Basically just a bunch of different gauge steel/nylon wires, in certain order.

But so far, some results of the three tested setups; first one seems to work on four of the thickest strings(e-a-d-g). That setup doesn't give strong enough output for the second thinnest string(b), though.

Second one is a bit of a mystery, as instead of increasing the output, when cover(with reflective surfaces facing the strings) is on, the output disappears(b-string).

Third one, again tested on a b-string, seems to be a step to the right direction, as it provides more output, when using the cover.

(http://www.elisanet.fi/kz1706/optical_pup/test_setups_so_far.png)

Distances/angles between the optical components on those setups are only arbitrary, but I think still a very good way to get a hunch, of how they behave, and affect the overall output.








Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on January 23, 2020, 07:02:23 PM
Addition to the previous testing theme; but this time it was done only with the hardest one - thinnest string(another e).
Angle between the optical components was changed, while the distance changes only a bit.

First one is a no-go, but gives good a tip, of what (or what not)to test next.

With the second one, I was aiming for an approximate angle, that would allow the ir-beam to actually reflect straight from the cover's brass 'mirror'. Afterwards it seems obvious, that the results were a lot better:

(http://www.elisanet.fi/kz1706/optical_pup/angle_test.png)

Needless to say, but although the four thickest strings(e-a-d-g) already give usable output with one of the earlier setup, that 70-degree setup will probably replace them, to squeeze even more output from them.





Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on January 24, 2020, 09:14:08 PM
The two thinnest strings(b-e) with the 70-degree setups were tested. There might be just enough output to keep their notes 'sustaining', to make the schmitt trigger's outputs usable.
That could be judged better just by plucking the strings, and listening the overall output.

As they are so thin, adjusting them for the sweet spots is rather nitpicking thing to do, though. If one doesn't mind the string material, nylon strings, that are generally a lot thicker, could be used instead. Personally I don't like the 'rubbery' feeling of the nylon strings, but who knows, I may well end up adding a set of them, when ordering the strings next time.
 
One thing was again confirmed with this kind of setup: the signal disappears immediately, when the string is bent. There could be a way to fix that, perhaps by using something like two pairs of senders/receivers per string, where the pairs are wired in series or parallel to form again one pair per string.

When reading back the thread, JohnHaine suggested diffuser. I had to look out for the definition of the word, and as I see it now, the light is 'scattered', making it to glow, instead of straight lighting, when it goes through the (shady?) surface.

I think I know at least one way(found accidentally at the beginning of the project) of making the ir-led's plastic surface to look not-so shiny(more like shady); simply expose it to superglue fumes, and that's it(maybe even dipping the led to acetone or xylene instead could work). 

Although I think it would greatly decrease the transfer of the ir-beam, it should be easy enough to test, how it works.

But in general, the project(while still having plenty of room for improvements) is slowly getting to the point, where it's time to make a simple circuit(6-to-1 -mixer), for the numerous 'audio-only' testings.

If that goes well, then there is yet another challenge: to get all the circuitry out of the guitar's body, to form a separate control unit.

Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on January 25, 2020, 07:58:42 PM
The whole setup, with almost all wires connected:

(http://www.elisanet.fi/kz1706/optical_pup/almost_all_wires_conected.png)

As for the 6-to1 -mixer for the output of schmitt triggers, I built a stamp-size one, with discrete 10k resistors. But, memory served, and I found a bag of 10 x 10k resistor networks from the shelf.

It was quite easy to make a nice and tiny 'plug-in' unit out of that. It's barely visible in the picture, but it's the orange one, on the upper boards right side, that has schmitt trigger -ic's in it.

Makes me a bit nervous to start testing out a mess like that. I don't expect instant success, though, as there could be hiding some 'cumulative' bugs.

On the other hand, with (almost) all the wires running wild connected, it looks more complicated, than it actually is.

If(when) there is any kind of success, only then it's worth diving into the 'sub-project', to tidy up(or remake) the wirings for something like.. more permanent setup.
 


 
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on January 27, 2020, 08:02:43 PM
After two days of testing, the output of the thinnest strings still lack usable output. Also there appeared a strange 'octave skipping' -effects on thicker strings, which should have enough output.

For that I suspect the not-so-optimal amplifier board. There is quite a lot of crosstalk between the strings, not only from the next string, but from all other strings. Meaning, that when observing only the thinnest string's output, others bleeded through as well.

The schmitt trigger -board was removed shortly after starting the testings, as it didn't make sense to use it with the amp circuit, that already produced not so good outputs.

So, back to drawing board. For the optical setup, I'm going to re-visit the one, where the sender/receiver 'stare at each other's eyes'. On the left is the older one, that should still work, and on the right is a possible new alternative.

I have some optoswitches, that have those kind of flat components inside. Should be an easy task to extract them from the optoswitch body, and test, if they are usable. When on the level with the string, they protrude only about 1,2mm above that string:

(http://www.elisanet.fi/kz1706/optical_pup/back_to_older_concept.png)

The housing will be sort of 'semi-open', where the component pairs are mechanically connected 'under-the string', to hopefully make them easier to install/remove. They need to be connected together, or the height adjustment becomes (not) very interesting. To prevent ambient, or plucking hand -effects for the ir-beams, again, a slim cover over the strings could be used.

One might wonder, why not to use the optoswitches, as they are? For a bass(at least for 4-string), that has more room between the strings, that could probably work. Otherwise they are too bulky, and the ones I have, the optical components have some play inside their housing, so not very good for precise height adjustment(as they should be secured with glue to stay in place).

As an opposite, one supplier on my list has smd(surface mount device) version of those available, but they are far too tiny for my paws/eyes.

I'm not sure yet, of what the amp board is going to be, though. 







 
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on January 28, 2020, 07:56:23 PM
Sketch for a new setup for the optoswitch components:

(http://www.elisanet.fi/kz1706/optical_pup/new_setup_sketch.png)

Model of the optoswitch is H21A2 by Isocom. Components came out easily, by pulling the 'lid' open with a sharp chisel, without even breaking their housing:

(http://www.elisanet.fi/kz1706/optical_pup/optoswitch_components.png)

Sender and receiver were push-fitted in place(perhaps some glue also needs to be used). One with yellow dot is the ir-led, while the one with red dot is a phototransistor. Printed part on the left is a testpiece of the to-be-printed base, to test the tolerances and height adjustment. So far it has gone well, and (hopefully)shouldn't take too long to get back to 'test-bench'.

It may need some modifications to fit the wirings, though. The concept will probably be same, as with previous setup, where the sender's wires come out from one side, and receiver's wires from the other side.

The components work, as expected. The physical specs of those flat components aren't usually mentioned in the optoswitches datasheets.
Although they can be simply measured, in some cases it could be better to see the actual manufacturers spefifications, and tolerances.

Sparkfun has datasheets of Liteon's LTR-301 phototransistor, and LTE-302 photodiode available on their site, as well as downloadable 3d-models, if memory serves. But generally all of those seem to be the same size, after all.







 
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on January 29, 2020, 09:45:13 PM
New setup almost ready for testing:

(http://www.elisanet.fi/kz1706/optical_pup/new_base.png)
(http://www.elisanet.fi/kz1706/optical_pup/printed_new_base.png)

Once the short-ish legs of the components are bent, they fit in just fine. That way, the wires that are to be soldered, stay outside of the base.

By using the smallest size heat shrinking tube, that I have, the legs shouldn't short between each other. But we'll see.

While sketching and printing the parts, I remembered seeing a picture of those flat components used in optical pickup somewhere. So that's where I got the idea.

It was Ron Hoag's invention. I have no idea, of how old that picture is, but if judging it by the thickness of the optical components, they look a lot thicker, so probably not very recent:

(https://news-cdn.softpedia.com/images/news2/Light-Music-Technology-On-Sale-The-Optical-Pickup-Patent-4.png)

Again, making an optical pickup to look that clean, without wires running around, there really isn't too much options, other than to drill holes for the wires to go to the back side of the guitar.

After all, there is very little information available of that pickup/setup. I have found only few sources, one which is on the same site, as the above picture:
https://news.softpedia.com/news/Light-Music-Technology-On-Sale-The-Optical-Pickup-Patent-52851.shtml (https://news.softpedia.com/news/Light-Music-Technology-On-Sale-The-Optical-Pickup-Patent-52851.shtml)

If only he had 3d-printer (or affordable cnc) technology available back in the days, whole electric(and why not bass and acoustic also) guitar scene could be a whole lot different, than what it is today.

Generally, as mentioned before, this project doesn't follow the same path, that commercially available products, which concentrate on removing magnetic pull, created by traditional electromagnetic pickups, to get the cleanest possible output/sustain from the strings.

Bit of (ranty, sorry about that)background; for a long time, I've been a fan of the analog syntesiser sounds. But, not a surprise, that to get those, one needs to be able to play keyboards(which could make whole thing much more simpler).

Although I have had some keyboards in the past, they ended up gathering dust and sold, as they don't feel as natural to produce sounds(pluck), as guitar does(personal preference).

Other options available today, in form of commercial products:

- Get the costly 'authentic' old analog guitar synth with a hexaphonic pickup, that had already tracking problems, when it left the factory.
- Get the digital guitar synth with a hexaphonic pickup, that uses the newest technology, to emulate analog synth(could do the trick, if you got the money).

It seems, that working, true analog guitar synths haven't developed at all in the past decades, to make them easier to use, as there hasn't been enough demand for the big manufacturers, that have plenty of engineers, and other resources, to develop them further.

I'm well aware, that those kind of devices require special playing techniques to suit the technology. 

But no matter how good/bad it is, that analog guitar synth -stuff seems to be very marginal these days. Maybe it was always that way.

End of the rant, and back to the project.

 

Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on January 31, 2020, 10:00:17 PM
New setup was tested with three of the thinnest strings (g-b-e):

(http://www.elisanet.fi/kz1706/optical_pup/testing_g_b_e_strings.png)

Outputs from the strings are now bit closer to be usable, than with previous setups. When they are mixed together after Schmitt triggers, chord harmonies are more audible, than on the lower frequencies (thicker strings e-a-d).

There is still that ugly sputtering, octave-skipping effect. One reason for that could be 'double clipping', where the amp board clips the signals first, and after that, the schmitt triggers clip it again.

On the other hand, actual analog cmos-based 'octaver' -device(divides the input frequency by 2, like Roctave divider)for the guitar, has a very similar behaviour, but it appears only when the signal fades out, or the input signal is too weak.

To get around that, perhaps an amplifier stage, that doesn't clip so easily, while producing huge amount of output, should be used. Have to find one first, that suits for the purpose, though.

There is also one stage, that is a part of the currently used amp board, which is placed before the 386-amp. It boosts the phototransistor output. Not sure, if it's an amplifier, or something else.
Generally phototransistors seem to have max. collector-emitter voltage, that is at least 30 volts. So far, I haven't explored it that much, and have used it only with 9 volts(like the rest of the amp board):

(http://www.elisanet.fi/kz1706/optical_pup/phototransistor_thingy.png)

At this point, one might think, 'where's the beef? let's hear the results!'.

I was merrily recording an audio clip, using trusty Windows 7- based laptop, that has an ancient version of Goldwave installed. I know, but it just works for simple tasks(or so I thought).
As usual, I listened the output with headphones, while recording. All seemed/sounded fine.

But when listening the resulting, saved audio file, it had a strong, phase shifter-like effect going through the zero-point, that 'cancelled' most of the audio, making it useless.
Previous audio clip was recorded using exact same setup, with no problem.

I have also a desktop pc, and another laptop to test, so maybe i'll manage to record a new audio clip, that is worth posting.

   
   
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on February 03, 2020, 09:00:45 PM
In the past few days I've looked a way to replace the 386-amp board with an op-amp based one. Test circuit(TL072):

(http://www.elisanet.fi/kz1706/optical_pup/op_amp_test_circuit.png)

It was just thrown together for breadboard, and probably lacks all of the some important components. But as it is, it gives enough output for testing.
Seems to work better by using a split power supply.

But in general, the lack of delivering enough output to keep the schmitt triggers 'squaring' long enough, to make the output to feel more like guitar-ish, still exists.

Then I had to rethink about the whole thing: I have already an overly powerful(and noisy) 386-based amplifier board, which should be more than enough for the purpose.
But in practice, is that much grunt for amplifying the phototransistor's output really even needed, as the end result is still far from usable?

So it was time to try a bit different approach to the problem. I remembered seeing something like positive- and negative input threshold voltages on the 4093's(quad schmitt trigger ic's, that are used so far in this project ) datasheet.

This picture is actually from 40106's(cmos hex schmitt triggers) datasheet, as it's much more clearer, than the old 4093's one:

(http://www.elisanet.fi/kz1706/schmitt_trigger_thresholds.png)

One thing, that came to my mind, was to bring the input signal between the Vp and Vn, by using an offset, and then adjusting it, to see how low it would go to 'tickle'(trigger) enough both limits.

There might be something in it, but I'll have to admit, that after trying that with a function generator and a scope, there is much more in it.
No matter, which way I tried to test that out, I just couldn't get my head around, of how it could actually be done.

Threshold voltages, although only approximate ones, are on the datasheet, and as the supply voltage is lowered, they lower also.

So the next thing to test was obvious; decrease the schmitt trigger's supply voltage. At 1,8 volts, the input threshold was under 0,1 volts, when testing with a square wave.
Needless to say perhaps, but at that level, the quality of the output never meets any of the standards.

Besides of that, I kept on going, and tested the bugger with a g-string. Yes, the output was a lot lower, but for some reason, 'squaring' was there, and it just kept on doing it longer, than ever before.
And that was by using the above 072-op-amp based circuit.

So far, cons of using that low supply voltage:

- output waveform has some mutations(although not necessarily lethal), when compared to clean square wave
- needs to be amplified/gated afterwards, to get back to the cmos-level

Then the pros:

- overall bandwidth of the schmitt trigger chip decreases drastically(down to few kilohertz), which should/could be good enough to reject radio-like interferences
- less amplification is needed

There is a drawback, when using optical components, that are extracted from optoswitch(or at least the ones I have), though. The phototransistor doesn't have an ir-filtering in it, so it is easily affected by the visible lighting.




 
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on February 04, 2020, 09:22:13 PM
I decided to take a final test for that noisy 386-based amp board, to see if it still has any use, with 1,8V supply fed schmitt triggers.
It appears to have, once its output levels are turned down enough.

Testing was done with three thinnest strings(g-b-e). There was a strong (4-5V) ~25kHz noise signal, that made the schmitt triggers go nuts.
In previous post I claimed, that the bandwidth of the schmitt triggers had decreased with lower supply voltage. Maybe it has, but not down to a few kHz.

Still I wanted to see, if that noise level could be lowered. By using an online low-pass filter calculator http://www.learningaboutelectronics.com/Articles/Low-pass-filter-calculator.php#answer1, I ended up making a quick test-plugin, that has 10k resistor and 1,5nF capacitor in it:

(http://www.elisanet.fi/kz1706/optical_pup/low_pass_filter.png)

Its cut-off frequency is at ~10kHz, and seemed to do the trick. After that filter, the noise level went well under 1 volt.

After some tinkering, the strings' outputs had quite decent rectangle shapes. Although the scope showed also more acceptable sustain of the plucked strings, it's only visual result.

I hate to go ahead of things, but if the results are still there, when listening to the outputs, the project has taken a tiny step to the intended direction.

But after all, if that goes well, the current optical/mechanical setup still needs a removable (as slim as possible)cover above the strings to be drawn and printed.
And the schmitt trigger board needs its own dedicated regulator, likely LM317-based, variable one. I have those already at hand.

What comes to audio recording setup, especially, after failing with the previous audio clip, I feel like 'meh, what else is not working, as it should'. Eventually that needs to be sorted out, though. 

Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on February 07, 2020, 07:46:30 PM
Latest setup ready for height adjustments of the pickups:

(http://www.elisanet.fi/kz1706/optical_pup/yet_another_setup.png)

To get reasonably stable outputs from the strings, for adjusting the height of the pickups for max. outputs, perhaps most time consuming part (at least on my guitar) is to track the peak frequencies, where the individual strings resonate, when using the small speaker as a resonator(mentioned earlier).

Using low enough outputs, that don't clip at the amp stage, makes it easier to find sweet spots.

I used to write those frequencies down, but they change from day to day. Not so much between the strings, but all of them have gone in frequencies tiny bit lower.
I guess, that's the way the wooden construction(mahogany body, maple neck) reacts to changes in air humidity.

But enough of that. Only after the height adjustments, it's worth to move on to the electrical side.

One thing, that popped to my mind, when testing, if it's possible to 'palm-mute' the strings, while the cover for the optical pickups is in place. 

It is almost possible, but as the printed cover is made of plastic, it has to have some extra thickness in it. If that cover was made of, say, out of 0,5 or 1mm brass sheet, it should allow a lot lower, 'slimmer' cover to be used.

What I mean by that, is that if one uses a traditional electromagnetic pickup, its usability could be expanded, when using it besides the optical pickup.

Making that kind of brass/other metal cover would require some serious skills, that I don't have, though.

On the other hand, one way could be making a mold, and casting some tin in it. Could be too smoky thing to do in my apartment. But, after all, who knows(http://emoticons4u.com/crazy/134.gif)
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on February 08, 2020, 05:29:40 PM
This time, the audio recording of the 6-to-1 mixed schmitt triggers was done straight to the laptops mic input. So no echo, equalisation or any other effects were used. Plain 'dry' output:
http://www.elisanet.fi/kz1706/optical_pup/testing_new_setup.mp3 (http://www.elisanet.fi/kz1706/optical_pup/testing_new_setup.mp3)

The schmitt triggers' output was bit too hot for the laptops mic input, so I did simply put a potentiometer between them, to the breadboard to turn down the excess distortion. That breadboard was on my lap, while plucking the strings, and kept on falling all the time..

But after all, I was just too impatient to test the audio output, to solder some wires for more usable/permanent level adjusting unit. 

When doing the previous, failed recording, when there was that weirdo cancelling effect, I used Zoom G3(guitar effects device) between the schmitt triggers and laptop.
I'll have to admit, that for a long time, I have been interested in exploring odd and strange audio effects. But that one, I can't even imagine, how to track it, or make sense, what it actually is.

Besides all that, came another idea of using individual covers for each string/pickup, like this:

(http://www.elisanet.fi/kz1706/optical_pup/individual_opt_pup_cover.png)

I haven't tested that yet, but if it works, the parts could be printed, while being a lot more 'stealth', than single, bulky cover.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on February 09, 2020, 09:04:24 PM
At this point, it's (finally) time to move on to making the electronic circuitry(amp, schmitt trigger, and ir-led adjustment -boards ) in more easily form to operate. That means basically removing them from the guitar body.

As the guitar is to be used only at the living room, for starters, one meter long cables should do. The plan is to use 7 for the ir-leds(could possibly be made out of an ethernet cable), and 6 for the senders/receivers(using shielded microphone cable).

I already tested a single pickup with a single, one meter mic cable, and so far, it seems to work. The end result, with all the cables/pickups connected, could be lacking, what comes to noise levels.
But as always, there is only one way to find it out.

If (when)all goes well with the wiring, then comes time to test, of how the schmitt trigger outputs could be refined further, and to see, do they(running at 1,8V) need to be amplified/gated to feed external cmos-based devices.

 
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: PekkaNF on February 10, 2020, 03:51:49 AM
This time, the audio recording of the 6-to-1 mixed schmitt triggers was done straight to the laptops mic input. So no echo, equalisation or any other effects were used. Plain 'dry' output:
http://www.elisanet.fi/kz1706/optical_pup/testing_new_setup.mp3 (http://www.elisanet.fi/kz1706/optical_pup/testing_new_setup.mp3)

......


Wow. I am surpriced that the output is that rich and even some warmth in it - like second harmonics or something "musical" distortion. Must be hard to find a sweet spot location for opto componenets.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on February 10, 2020, 09:24:50 PM
Wow. I am surpriced that the output is that rich and even some warmth in it - like second harmonics or something "musical" distortion. Must be hard to find a sweet spot location for opto componenets.

Pekka, yes, for some reason, that seems to be the nature of the true analog 'synth' -sound. Produced harmonics are certainly very complex, providing that 'something', which makes it sound the way it does.

So, that's how the analog hex fuzz sounds. There are some videos on Youtube about commercially available ones, but generally they have a lot more mellow outputs(probably to suit for larger user base), than mine has.

What comes to adjusting the height of the pickups for sweet spots, I'm not sure, but it could be done so-and-so just by listening the outputs, judging the result by how long the string rings, and therefore cause the schmitt trigger to 'squarify'.

To lessen the 'guesstimation' -factors, using a function generator and scope help a lot.

The process isn't that difficult, but can be tedious. Fortunately, it needs to be done only once(assuming the string heights remain the same).
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on February 12, 2020, 06:57:07 PM
After the wiring for the new enclosure is done, I'm going to test the idea of the previously mentioned individual pickup covers.

At first, for the enclosure, I thought about ordering a Hammond-like aluminum one right away, but decided to hack it together from pieces of wood I have lying around.

As the project is in testing phase, I didn't want to bother with possible need of the isolated/insulated connectors, that metal enclosure might well require.

Could take some time, as I'm not yet sure, what kind of connector to use for the enclosure outputs.

One likely candidate is a cd-rom ide-cable(which I already have at hand), that has more than enough pins(39) for possible 'extended' future options(like modulating each ir-leds individually, using external signals, if needed).

Also each schmitt trigger would have individual outputs for an external mixer, and/or other processing purposes(to convert square wave to a triangle/sine one, or to feed some envelope followers/filters/oscillators etc.).

Lots of babbling, but in short: the enclosure mentioned will include only the circuitry used so far. Rest is about making easily accessible connections for further testing, mainly for breadboard.


Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on February 16, 2020, 08:34:56 PM
Not really an optical pickup related, but more about how the external enclosure has turned out. Bit too dark and fuzzy photo, and drawn one:

(http://www.elisanet.fi/kz1706/optical_pup/enclosure_1.png)(http://www.elisanet.fi/kz1706/optical_pup/enclosure.png)

I used chipboard to add some extra weight for it(otherwise I hate to work with that stuff). Kitchen aluminum foil was used for shielding to see, if it has any benefit for that noisy amp board.
The cover also has foil glued in it.

Cables from the guitar(pickups and ir-leds) will go through printed strain relief clamps. Later they will be replaced with two D9-, or a single D15 connector.

Using cd-rom ide-cable for outputs, as mentioned before, didn't work that well.
As a male part, I used pins soldered to perfboard, but when pressing/connecting the female part in, some pins popped out on the other side, with the copper spots they were soldered to.

Simple pin headers were used to replace them(as on the above pics).

That box has a 7809-regulator in it(as the testings were done with 9 volts from the variable power supply), and will be powered with 24V/1500mA power supply(from an old scanner).

Combined current drawn by the amp board, schmitt triggers, and ir-leds is only under 100mA, though.

By the way, when looking videos on youtube about hex fuzz, besides the commercial ones, there was one guy, that had done a diy-version(or so I assume) of it.
Of course I forgot to bookmark it, and now can't find it anymore.

He demonstrated it on several videos on his channel. A big let down, as on numerous other youtube videos also, is to show only the results, and to refuse/to not bother to reveal any of the details, of how it's done.

I mean, what's the point making those kinds of videos anyways.



Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on February 18, 2020, 08:50:43 PM
More of the interfacing hassle. Yes, it is (very)boring, but has to be done. Current version of the stuff:

(http://www.elisanet.fi/kz1706/optical_pup/installing.png)

Printed 'boxy' part on the guitar consist two sandwiched perfboards with pin headers, to plug in the sender- and receiver wires.
Another one is a strain relief clamp. They make it a lot easier to move the assembly around, as I have to do it often, to free some table space.

That wiring/connecting/interfacing is very finicky to work with. Apparently some of it needs to be changed at some point.

But for now, I'm going to test it as it is. I'll be surprised, if it works, as expected. If not, it's again a good chance to learn new project-concerning things.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on February 20, 2020, 07:54:25 PM
I managed to assemble the circuits inside the enclosure, and after stomping several bugs (which were actually stupid mistakes) out, they work, as expected.

Settings for the amp board/schmitt triggers/ir-leds are still same, that were used, when the circuits were on the guitar. As a sort of a reference.

The overall noise level, although not seemingly that high, is enough to reach the schmitt triggers. The receiver/phototransistor cables are shielded, except inside the small box on the guitar.

When covering that box with a hand, it decreased the noise just a bit, so that's where the 'leak' is. As a last attempt, I'm going to try to shield it with aluminum foil.

Whether it works or not, I kind of saw that coming(shielding problems/noises), as most, if not all, optical pickup manufacturers place the amplifying circuitry as close as possible to the source.

If only I had an ability to work with smd(surface mounted device) components, all the involved circuitry would be already 'stealth' enough to fit nicely inside/outside of the guitar.

After all, if the shielding of the 'box on the guitar' fails, it's probably time to redraw the involved circuits from the very beginning, as the current ones are very clumsy, and were just thrown together for testing purposes. Maybe even fusing them together to form a single circuit board, without unnecessary pin header -connections.

But time will tell, as Frankenstein would have said it(http://emoticons4u.com/crazy/335.gif).
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on February 22, 2020, 07:11:33 PM
Shielding that small box in the guitar doesn't seem to have noticeable effect, to lessen the overall receiver/phototransistor noise.

Although the wiring for them is made of a shielded, individual microphone cables, there are differences between the pickups, in a way their noise outputs and -levels(with zero input signals) look.

Perhaps a shielded, single 6-core cable could be a better choice for that. But who knows, before testing. I'll probably add some of that to the next order.

After all, I really would like to keep the current setup, instead of redrawing/remaking the whole circuitry to fit in the guitar body.

So the next challenge is obvious; to lessen/attenuate the overall output noise levels with external circuitry, without knowing, if it's possible at all.

Schematics for simple noise gates are available on the net, and so far, I have tested one, that is based on the optoisolator(Led/Ldr pair). There might well be something in it, but it needs to be modified to suit for this project.

Probably not worth the trouble, but no matter what, I'll have to find out, how deep that rabbit hole is far I can get, before hitting the wall.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on February 23, 2020, 07:10:13 PM
While tinkering with the optoisolator based noise reduction for the amp board, I accidentally found the major source of the noises, that appeared, after the circuits were put to an external enclosure:

(http://www.elisanet.fi/kz1706/optical_pup/noise_sources.png)

Those pots, that were added afterwards, seem to act like radio towers. Just by touching the metal wiper part, the noise immediately decreased a lot.
Although the noise source is located, I'm not quite sure yet, how to shield those potentiometers causing it.

But after all, I'm rather relieved, that the noise source wasn't that much about the cables, or other wirings on the guitar side.

The residual noise can be suppressed even more, by using something like the noise gate, that I've been testing.
At the moment, it's a bit quirky one, until I find a way to smoothen out the input signal driven led's response.

The noise gate circuit itself is quite simple, consisting one npn-transistor, that is fed by the signal from the amp board, to drive the led of the diy-optoisolator.

There are few other components involved also, but I'll have to do more testings to see, how they work.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: WeldingRod on February 24, 2020, 09:25:04 AM
Capacitor to ground on the pot mounting nut...

Sent from my SM-G892A using Tapatalk

Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on February 24, 2020, 09:32:31 PM
WeldingRod, that's a good idea, but the pots are trimmers, and don't have mounting nuts in them. But on the other hand, it could be worth testing, if at first replacing one of them with actual pot, that has a metal cover and mounting nut, affects the noise level... hmm, we'll see.

The noise gate, that I've been tinkering with, is based on the circuit on the left(source: https://sound-au.com/project145.htm):

(https://sound-au.com/p145-f1.gif)

Although it is for switching, it could be abused used as a sort of 'automated volume pot', by substituting the Vctl input with an audio signal.
To drive the led, I've been using breadboaded circuit like this:

(http://www.elisanet.fi/kz1706/optical_pup/noise_gate_test.png)

Component values on the above pic aren't necessarily same anymore, as I change them during testing, to see the differences.

So far, after plenty of adjustments, it seems to be almost usable. Drawback is, that it decreases the overall signal levels from the strings/pickups also.
To simplify its construction, instead of using each string to drive its own led, could be to drive all the leds with a single input from the traditional electromagnetic pickup.

Might seem odd, but actually there is no need create individual volume envelopes for each string/pickup, as the whole point is to use the device only for polyphonic(chords) purpose.

Monophonic stuff(like solos) could then be done by using plain old electromagnetic pickup, as needed.

To get back to the noise problem, quickest and dirtiest workaround is possibly to use a foot pedal/switch to control/kill the output, once the chords fade out.

I'm not sure, if I should even mention one of my mad mood ideas. But here it goes, anyways. The thing would be to use 4046-based phase locked loop(pll) -circuits for each string, to track the frequencies.

When the frequency is stable enough(like after plucking the string), the pll can lock to it, providing 'yes' -signal to a certain pin.

After that plucked note fades out, noise takes over. If the noise is random enough, the pll just wanders, and can't lock to it, providing 'no' -signal to that very same pin.

But in the end, I haven't yet tested, of how the externally installed circuitry sounds, with all the noises. Time to find that out.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on February 25, 2020, 06:49:06 PM
Time for an audio testing, and the result, although rough and noisy, wasn't as hopeless as I expected. Again, raw output from the schmitt triggers recorded to laptop:

http://www.elisanet.fi/kz1706/optical_pup/testi_2.mp3 (http://www.elisanet.fi/kz1706/optical_pup/testi_2.mp3)

All the six strings were plucked to form the chords/sounds, and to mask the noises. If partial chords were plucked, noises from 'idling' strings/pickups would mask them.

It seems, that every string/pickup needs their own, individual noise gates. That previous 'touching the amp boards trim pots with finger' -trick doesn't work anymore, as all the pickups are connected.
Infact, it makes the noise problem even worse.

As mentioned before, I'm willing to keep the current setup, as it's so much easier to move around, and to work with, as all the circuitry is in an external enclosure, and the cables between it and the guitar are secured with strain relief clamps.

So, on to the noise problem. I'm going to test an optoisolator-, and 4046(pll) -based ideas.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on February 28, 2020, 07:56:51 PM
After trying out some stuff about reducing the noise levels, I finally got this frustrated feeling in my stubborn head, that I'm beating a dead(or actually very noisy and farty) horse.

It's time to ditch the 386-based amp board, no matter what. When shortly testing two of the pickups with only the phototransistor amp-thingy(that are also in front of the 386-ic's), noise levels were already many times lower:

(http://www.elisanet.fi/kz1706/optical_pup/phototransistor_thingy.png)

The above circuit will likely still be a part of the forthcoming circuitry. It seems to (probably) have enough output on its own, to feed the schmitt triggers. More testing with thinner strings is needed to confirm that, though.

On the other hand, the mechanical setup appears to work, as expected, apart from two of the thickest strings(e-a).
They are thick enough to almost cover the entire ir-beams from sender to receiver(which have 1,5mm diameter 'eyes'), providing erratic, octave-doubling effects.

Their optical components might need to be replaced with 3mm ones, but, as always, one thing at a time.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on February 29, 2020, 06:50:21 PM
When looking an alternative for the 386-based amps, I ended up testing a 4049(Hex Inverting Buffer and Converter)-based one (source http://electro-music.com/forum/topic-51275.html).
Although the schematic on that page uses two stages, I cropped the second one out, to see if the thing works with fewer parts:

(http://www.elisanet.fi/kz1706/optical_pup/4049_amp_2.png)

After breadboarding, and some usual tests with thickest, and thinnest strings outputs, and with schmitt triggers, yes, it seems to be working. Not only that, but it's also a lot more responsive to gain adjustment, than the 386-amps were.

Nice thing about that 4049-chip is, that it has all the needed six 'amps' in a single 16-pin chip.

There is one serious precaution, though. I almost fried the chip(it got very hot), when forgetting to connect unused inputs to the ground(or to +, as the datasheet says)(http://emoticons4u.com/crazy/1087.gif).

As before, the noise wasn't much of a problem, when testing one string/pickup at a time... I'm not expecting wonders, as there is a big chance, that combined pickup outputs combine the noises also.

One possible way to minimise that, would be to mount the circuitry again, in the guitar. If that single-4049-chip-amp stuff works, the whole circuitry could then take a lot less room, than the previous 386-amp one did.

Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on March 02, 2020, 08:33:54 PM
The phototransistor- and 4049 amp board is ready for drilling:

(http://www.elisanet.fi/kz1706/optical_pup/phototrans_and_4049_amp_board.png)

Hopefully there isn't any errors, as I checked the layout multiple times. The size of the board is 72 x 68 mm. I could have made it smaller, but then I would have to (again)cram the parts in.

Besides that, I probably should have made it even bigger, as it's all analog circuitry. "The bigger and uglier it is, the better it sounds"(http://emoticons4u.com/crazy/670.gif)

But seriously, as there are six 4049-based amplifiers so close together, their inputs and outputs should have some distance between them.

When doing the previous breadboard testing, they don't seem to do the hard clipping, as the 386-based amps did.




Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on March 06, 2020, 06:38:02 PM
New amp board:

(http://www.elisanet.fi/kz1706/optical_pup/new_amp_board.png)

I tested all the six sections, and they seem to work, as expected. As usual, square wave was fed to the ir-led of the pickup(from the earlier mechanical setup), and the phototransistor was connected to the circuits input:

(http://www.elisanet.fi/kz1706/optical_pup/ir_led_phototrans_pair.png)

There is one thing, that bothers me about that 4049-chip, though. While testing the sections one at a time(while others were not connected), it did hog constantly about 50mA(at 9V), and got warm.

Bit like on the breadboard, where I forgot to connect unused inputs to the ground, but not that bad.

From that came this shady logic conclusion, that the inputs might act like weathercocks, that aren't tied to anything during the storm. So they rotate at forever increasing speed, until they get glowing red, and therefore get very hot.

But enough of that. I took a look of other 4049-based circuits on the net(there are lots of them, as that chip was/is used in some commercial, and in many diy guitar fuzz pedals), and at least some of them have 1M resistor between inputs(that are in use) and ground.

Not a big deal, so I drilled holes for the 1M resistors, and soldered them to the circuit. But they didn't help at all. Am I missing something important here? 

I have tinkered with other cmos-ic's(mostly for guitar effect purpose, some counters, and pll) before, but never had problems with excess power consumption/heat.

Let it be said, that I read somewhere, that this chip(4049), when used as an amplifier, has a notorious reputation of having wildly different current consumption, even between individual chips from the same manufacturer.

I have two spare chips, and will probably test, how they compare.

But in the end, if the circuit works, regardless of current consumption and warming, it's okay by me, as I never intended to rely on batteries to use it. I'm more worried of how the chip lasts, being warm all the time it is used.

Also, one thing to test is to connect all the pickups to the circuit(to'occupy' all the inputs), to see if it makes difference.

 
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on March 07, 2020, 08:21:26 PM
Audio test using the new amp board and schmitt triggers, again without any effects:
http://www.elisanet.fi/kz1706/optical_pup/testi_3.mp3 (http://www.elisanet.fi/kz1706/optical_pup/testi_3.mp3)

It seems, that changing the amp board was a step to the right direction. There is very little noise, when I tested it with the cables, and practically none of that noise is strong enough to get through the schmitt triggers.

Also less distortion(although some of it could add nice texture to the sound), as the 4049 doesn't clip the signal as hard as 386 amps did.

There is one downside, though. When plucking a single string, or playing solo, the outputs are very weak/lacking(or outright unpleasant). Don't know why that is. But when several strings are plucked(as chords), somehow the outputs 'morph' together, having a lot more powerful, and usable output.

What comes to the power consumption of the 4049 chip, I tested another one, and it acts just the same. I guess that's just the way it works in the current circuitry.
As the power supply has a lot more beef(24V/1500mA), than needed, I can live with it.

So next thing to do, is to fit the new circuitry to that external enclosure, that I made earlier, and some wiring.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on March 09, 2020, 07:26:57 PM
I've been eagerly waiting to get to the point, where the circuitry is worth putting inside the external box, and here we are:

(http://www.elisanet.fi/kz1706/optical_pup/one_step_ahead.png)

No smoke or sparks, when I shortly tested all the six sections, they seem to be working just fine. Also no extra noises on the outputs.

That certainly doesn't mean, that the project is finished. It just means, that all the(well most of it) wire hassle is now out of the way.

Lots of aspects to test, including 'stealth' covers for the pickups.

Also to see, if I can make sense about that 'soloing'(playing single string) -problem mentioned earlier. There might be some strange phase cancelling stuff going on, that makes plucked single strings to sound so weak. When looking at individual string outputs on the scope, they are rectangular, and should sound, like fuzz does.

There is now less crosstalk between the strings/pickups/sections, when compared to 386-amps, but it still exists, and that alone could cause phase anomalies between the strings.
Almost like the next strings(that are muted) pickup(s) 'loot' most of the plucked single strings signal somehow.

Once I get into it, I'll make a diagram, which hopefully makes babbling above less fuzzier(pun intended).

After all, now it's good time to focus on testing/expanding/exploring the systems usability further.





Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on March 13, 2020, 06:56:47 PM
It seems, that the 'weak single string' -problem has something to do with the way I used to mix them together. So far, 10k resistor network like this, is what I've used:

(http://www.elisanet.fi/kz1706/optical_pup/res_network.jpg)

I have a sneaky suspicion, that mixing sources, which have exact same output levels(like schmitt triggers in use) is the cause for that 'cancelling' -anomaly.
More proper audio mixing circuit is on my(ever growing) to-do list.

When the outputs are listened one by one(not mixed together), they sound a lot more solid, and the way they should.
So I guess it could be possible to use each output for individual purposes.

One example, of what I mean by that, is, that one(string's) output could be panned to the left of the stereo field, while other is panned to the right. 
Another example is to drive one output to echo effect, while other one goes to some kind of cmos-based device(like up- or down counter). 

Schmitt trigger circuit, that I use, has probably too low output levels to drive cmos-level devices, as it uses ~1,8V supply to lower the input thresholds. I haven't tested it yet, but I think that very mild amplification of the outputs should be enough to bring them back to cmos-level, if needed.

After all, there are six outputs to boot for what ever effect combinations. I could say, that it's like some form of an analog synthesiser, but naah, I'm not going to say it(http://emoticons4u.com/crazy/296.gif).


One thing, that might increase the sustain of the thinnest strings a bit further, would be to use Darlington phototransistors. But as they should be "side looker" -ones, there are only few types of those available.

Some of them are thicker(2,5mm), which makes them quite difficult to fit in, or require whole new mechanical setup, when compared to slimmer 1,5mm ones.

Anyways, it would be interesting to test them(1,5mm Darlington ones) with current electrical setup. Sourcing them seems to be bit difficult, though. But again, we'll see.
They aren't that necessary, but could add some 'kick' to the project.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on March 15, 2020, 08:05:07 PM
When testing breadboarded, simple single transistor amplifier to see, if the schmitt trigger levels could be increased that way to the cmos-level, there was suddenly this repeating noise pattern, where noise was on for 1 second, and 2 seconds off.

After a while, I was ready to open the external box, where the circuitry is, and to dig it all out. But no, luckily it wasn't necessary. When I removed the lid of the box, shortly after that, the noise disappeared.

After some head scratching, I noticed, that the 7809-regulator chip was rather hot. I checked its datasheet, and there it was: 'Thermal overload protection' caused repeating noises.
The whole circuitry draws 100mA, or less, so it was kind of surprising(at least for me), how hot it gets.

Now the regulator board hangs outside of the box, and all works just fine.

What comes to the transistor amp circuit, after some tinkering, it seems to provide enough gain/amplification. Form of the output isn't perfect rectangle/square wave, but as long as it 'triggers' external cmos-devices, it should be good to go. Next thing is to test that in practice.

Hopefully it's the last amplifier circuit needed, as there are few of them already in the main circuitry.



   

 
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: BillTodd on March 16, 2020, 09:48:14 AM
Quote
The whole circuitry draws 100mA, or less, so it was kind of surprising(at least for me), how hot it gets.

The dissipation is the product of  the the current (0.1A) and the voltage drop across the chip (~2V minimum for a 5v device so 7V input), so your device is trying to loose at least 0.2W of heat a TO-220 package will have a typical thermal resistance of 70'C/W  so expect at least +14'C over ambient without a heat-sink .

If your driving the regulator with more volts 9-12v expect  a lot more heat :-)

Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on March 16, 2020, 09:13:17 PM
Bill, no wonder then, that it gets that hot, as I'm driving it with 24V/1500mA supply. As the regulator chip is 9V 7809, 12 volt supply should be enough.

In fact, I used variable psu on earlier testings, and it was feeding the circuitry at 10 or 12 volts, and the reg. chip stayed a lot cooler.

Thanks for pointing that out :thumbup:.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on March 18, 2020, 06:53:13 PM
Now, that the transistor amp circuit is built, the output levels should be good to go, to feed other cmos-based devices, or effects.

It brings the schmitt trigger outputs(about 2-3 V p-p(peak-to-peak)) nicely to ~9 volt p-p output at 9 volt supply. Very quick and dirty, and the resistor values were chosen simply by tinkering first with potentiometers, to find suitable output. Capacitor values were chosen by looking on the scope(and what I had on my shelf), which made the output to remain closest to square/rectangular wave. Pretty scientific approach, eh?

But after all, the frequency range of the strings/outputs is below 1Khz(unless one insist on shredding on the thinnest string on the frets above 12th one).

Only one section is shown, but as the circuits before, it also has six of them:

(http://www.elisanet.fi/kz1706/optical_pup/transistor_amp.png) 

One, or few other outputs could then be clipped down with something like 5V zener diodes, if needed. Don't know about that yet, as I'm going to take a bit of a break from the guitar/pickups -involved circuitry, and take a look, what kind of cmos-devices I have, that could then be driven with those pickups/outputs.

So far, I have fiddled with 4046 pll(phase locked loop) -ic, just by feeding it with function generator, and listening to the output.

I used to tinker with that chip years ago, so it isn't entirely new thing for me.

There are so many different component combinations/options to alter, of how it works/sounds. This is only one variation of them, that tracks the frequency of the signal fed to it:

(http://www.elisanet.fi/kz1706/optical_pup/pll_testi_4.png)

That chip has a vco(voltage controlled oscillator) in it, that runs at tracked input frequency, which could be interrupted, making some kind of "sample and hold" -situation, where the played note could be freezed/sustained to play longer, than the guitar string vibrates. Almost like on keyboard, that plays the note as long as the key is pressed.

The idea for that came from: https://hackaday.com/2015/08/07/logic-noise-4046-voltage-controlled-oscillator-part-one/

There is a lot of theory based stuff, of what that chip does, how it does it, and so on, for those interested, but I just don't understand it.

But that chip(basic version CD4046, not sure about the exotic, high frequency variations) is a very good one for testing on breadboard, as it is practically impossible to fry it out, unless intended.





Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on March 21, 2020, 09:53:40 PM
It seems like I'm getting more and more drawn into testing, how different cmos-based contraptions sound. So far using breadboard, and function generator, and a small amp for listening.
I feel tempted to test with guitar/pickups, but the concepts/results are somehow easier to follow with simpler test setup.

This is going to be rather long off-topic babbling, and I should perhaps start another thread, considerig the 'after-effects'.

I was looking info about sawtooth generators on the net, as I've read, that they have a lot more harmonic content, than plain square waves do. But seemingly, making decent sawtooth generator isn't necessarily that simple.

I have, as long as I can remember, liked Hammond organ sound, and Moog(analog synth) also. I'm not actually looking for replicating those sounds, but to see, what could be achieved using simple circuits.

What comes to that sawtooth generator, I thought that 'does it really have to be in traditional sawtooth form, that was used on so many analog keyboards?'.

Then came the idea of some kind of primitive "sampling" technique. After more searching, I found a name for it - staircase generator.
There are schematics, of how to make a proper one, but again, I started looking for other(simpler) ways to test the idea.

Back to the shelf, to check, what chips, or other stuff I have at the moment. There was 4040(12-stage binary ripple counter), which was then test subject.
I cheated a bit, and did some simulations, to see, if it's worth breadbording.

Circuit itself:

(http://www.elisanet.fi/kz1706/optical_pup/4040_staircase_test.png)

The output waveform is not, what I expected, but nevertheless, it sounds like a cheapo analog synth. Good enough, so I breadboaded it, and yes, it sounds very much the same, as in the simulation.

One big drawback is, that the frequency of the input signal is divided down a lot. To get the output frequency to match the input one, I did some testings with 4046(phase locked loop), that could be used to multiply the frequency by the factor, that it's divided by. 

I'm not sure yet, if it works in practice. More testings ahead.
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: Yarrrrr on August 25, 2020, 08:22:01 PM
I stumbled upon this thread as I have been researching optical pickups myself and came to the same conclusion that there is barely any information about it. But what I was looking for was more of a drop in replacement for a normal humbucker pickup which led me to the oPik design.

I've got a little test setup for the thickest string: 


Oscilloscope output: 


Audio output: https://www.dropbox.com/s/dug6chet2pw6jv7/test%20%233.mp3?dl=0

I am currently working on building a shielded enclosure to improve the signal to noise ratio, and trying to make this all fit in the size and shape of a normal pickup.

Something like this: 
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on August 26, 2020, 03:28:43 PM
Yarrrrr, welcome to the forum. It would be interesting to see your take on an optical pickup. If memory serves, there was some pictures/details in the oPik's patent, like an approximate angle between sender and receiver.

I remember using that patent's pictures as a basis, when I tested, how the infrared light reflects from the string(s), and what kind of output signal it produces. Obviously, when moving to thinnest strings, the output level decreases also. So yes, as good as possible shielding is needed.   
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: Boop on November 23, 2021, 05:38:01 PM
Hi,
Joined the group for this post!

Hopefully this thread isn’t dead, maybe this can lead to its resurrection.

Played with this a little bit some years ago.  Didn’t go much further than hooking up a photo diode and an IR led running into a guitar amp directly, or maybe it was a mixer?  Got output, was very excited, then life “got in the way”. 
But I thought I’d put these here from old Make magazine articles and associated links:
https://makezine.com/projects/infrared-string-bass/
https://www.slideshare.net/engrmali3/infrared-string-bass
There are more links that I’ll have to find, but this is what I have time to give right now.

 :worthless:
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: Yarrrrr on November 23, 2021, 06:52:38 PM
Hi,
Joined the group for this post!

Hopefully this thread isn’t dead, maybe this can lead to its resurrection.


I got to the point where I have a working prototype that I am dissatisfied with. But with my lack of experience in electronics and the amount of effort I put into trying to improve it which amounted to nothing has me quite discouraged.

More details with pictures and audio examples over here: https://www.edaboard.com/threads/guitar-photodiode-amplifier-signal-to-noise-ratio.396736/post-1705241
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: sorveltaja on November 27, 2021, 08:08:25 PM
Hi,
Joined the group for this post!

Hopefully this thread isn’t dead, maybe this can lead to its resurrection.

Played with this a little bit some years ago.  Didn’t go much further than hooking up a photo diode and an IR led running into a guitar amp directly, or maybe it was a mixer?  Got output, was very excited, then life “got in the way”. 
But I thought I’d put these here from old Make magazine articles and associated links:
https://makezine.com/projects/infrared-string-bass/
https://www.slideshare.net/engrmali3/infrared-string-bass
There are more links that I’ll have to find, but this is what I have time to give right now.

 :worthless:

Welcome to the forum, Boop. Yeah, it's rather good start to test a setup for an audible output. That's how I did. I don't remember how the progress went, but it's documented in this thread, stage by stage, of how I got the strong hexaphonic fuzz sound that I was after for a long time. Of course that isn't everyone's cup of tea, but hopefully in this thread are some things to consider, when one wishes to experiment with optical pickups. Remember that this project is based on a lot of trial and error testing. When something worked, I used it, and if not, ditched it.   
Title: Re: Diy optical pickup for guitar -- is it possible?
Post by: Boop on December 01, 2021, 01:25:38 PM
The analog sound synth-y distortion is neat (IMO)!  I hope you do get a chance to check out the links I posted, as in addition to the cool sound you got, I also enjoy the “natural sound” and other options this technology could offer (Along the lines of Hoag, Opik, optical microphones, etc.).

That said, I still dig my Unifuzz that plugs two prongs directly to mains voltage!

https://www.semanticscholar.org/paper/Reflective-Optical-Pickup-For-Violin-Leroy-Fléty/fc7eb46e3be1ccc9a2f62ce9710cfa14f4b5dad6

https://d-nb.info/1020135263/34

https://spie.org/Images/Graphics/Newsroom/Imported-2016/006681/006681_10_fig1.jpg

https://www.optoacoustics.com/industrial/optimic-microphones