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Diy optical pickup for guitar -- is it possible?
sorveltaja:
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:
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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.
sorveltaja:
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.
sorveltaja:
The whole setup, with almost all wires connected: [ You are not allowed to view attachments ]
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.
sorveltaja:
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:
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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.
sorveltaja:
Sketch for a new setup for the optoswitch components:
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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:
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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.
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