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Diy optical pickup for guitar -- is it possible?
sorveltaja:
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:
Circuits involved:
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.
russ57:
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
sorveltaja:
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.
WeldingRod:
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
sorveltaja:
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:
Same with an idea for height adjustment for the individual sender/receiver pairs, using M2 screws:
Contacting elements could be made of the header on the left:
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:
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.
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