Author Topic: Diy optical pickup for guitar -- is it possible?  (Read 4762 times)

Offline sorveltaja

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Re: Diy optical pickup for guitar -- is it possible?
« Reply #75 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

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.


Offline sorveltaja

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Re: Diy optical pickup for guitar -- is it possible?
« Reply #76 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:


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.

Offline philf

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Re: Diy optical pickup for guitar -- is it possible?
« Reply #77 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
Phil Fern
Location: Marple, Cheshire

Offline sorveltaja

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Re: Diy optical pickup for guitar -- is it possible?
« Reply #78 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:



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.

Offline sorveltaja

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Re: Diy optical pickup for guitar -- is it possible?
« Reply #79 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:



-- 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:



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.   






Offline sorveltaja

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Re: Diy optical pickup for guitar -- is it possible?
« Reply #80 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.



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:



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:




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 ).

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. 





 

Offline sorveltaja

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Re: Diy optical pickup for guitar -- is it possible?
« Reply #81 on: January 18, 2020, 08:40:54 PM »
The cover is now ready for testing all the strings:



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':



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.





Offline sorveltaja

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Re: Diy optical pickup for guitar -- is it possible?
« Reply #82 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:



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:



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.



 


 

Offline sorveltaja

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Re: Diy optical pickup for guitar -- is it possible?
« Reply #83 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:



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.