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Diy optical pickup for guitar -- is it possible?
sorveltaja:
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
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.
sorveltaja:
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:
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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 concentrating 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.
philf:
--- Quote from: sorveltaja on January 12, 2020, 03:48:56 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. ..........
--- End quote ---
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
sorveltaja:
Phil, that's a very good point. After a bit of sketching, the 90 degree setup, and then same with a cover:
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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.
sorveltaja:
After thinking of testing the rest of the older setup, mentioned in previous post, which was similar to this:
[ You are not allowed to view attachments ]
-- 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:
[ You are not allowed to view attachments ] [ You are not allowed to view attachments ]
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.
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