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Diy optical pickup for guitar -- is it possible?

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sorveltaja:
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.




 

sorveltaja:
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:


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:
 

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.


Closer inspection revealed, that all the IR component's "eye" -surfaces had gone dull, because of the cyanoacrylate fumes .
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:


There are 12 holes, that go through the wood:

 
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.
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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. 

RussellT:
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

russ57:
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

philf:
I too wondered what the advantage could be and found this:

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.

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