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Diy optical pickup for guitar -- is it possible?
sorveltaja:
John, thanks for the reply. Yes, there has been plenty of problems with the previous setups. Current mechanical/electrical setups aren't hassle-free either, and are more like testbeds for different concepts.
I guess, that when the string stands still in the ir-beam, only its shadow is detected, but as it has no motion, the receiver has nothing to generate. Perhaps a bit like a motion detector.
Movement of the string, at the very time, when it's plucked, could be seen as a very slow movement, as the plectrum/finger 'drags' it, and releases.
After that, when looking the string at the end, it moves like a jump rope(in exaggerated way).
I have thought of using a 'common' or single light source(consisting multiple ir-leds) for all the strings, but there is one thing, that I have noticed. The string thickness seems to have an effect, when adjusting the sender/receiver pair for the maximum output.
Also, if the receiver gets too much light from the sender, it goes 'blind'(maybe saturated), and doesn't respond anymore. That's what I have observed, while testing different mechanical setups so far.
Meaning, that if one setting works for one string, it needs to be altered for the other to fit.
That considers only the setups, that I've tested so far, which use single receiver/sender -pairs.
I wish I could explain all that better, but many things appear, when using components for the purposes, which they aren't designed for.
And, no need for apologies. Constructive input is always welcome.
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What comes to the project, again another mechanical setup, where the sender/receiver pair distance is ~15mm, and the angle between them is 120 degrees:
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I already tested it on the thinnest string, and the output was there, not necessarily better than on the previous, 90-degree configuration, but I just had to choose one of the setups, to move on with the project.
sorveltaja:
Three pickups in place for the first audio test. Another three 386 amp ic's are still missing:
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Again, that kind of mechanical setup's pickup outputs get easily disturbed, when moving hand over them.
They probably have their uses, but the strings should be plucked near the neck to avoid that.
One commercial maker uses 'strings-through-the-bridge' configuration for their guitars and basses, which doesn't have that problem.
Earlier I tested somewhat similar concept(where the sender/receiver "stare each other in the eyes"), although it had a bit different approach. I might get back to that, after all.
Results of the current setup: what comes to the 386-amplifier circuit, I wanted all the gain and boost it could ever offer. Now, that I have it, when listening to the output, it's overly raw, and very tricky to control in any way, as I left the gain pot out of it. It produces all kinds of farty sounds on its own, and isn't too responsive anymore.
In this case that amp clips very hard at x200 gain, which could be helped to some extent by increasing its supply voltage to get more 'headroom', but I'm not looking forward for that option.
So, as the mechanical setup will change, also the amplifier circuit has to be modified.
For the audio test, I didn't even bother to use schmitt triggers, as the output is beyond erratic already.
But all that aside, there is a hint of the effect, that I'm after, in the recorded masterpiece clip, in form of harmonies, which was made using the current setup:
(zipped mp3 attached)
sorveltaja:
I tested if the gain pots could be added to the current amp circuit, to make it more usable. It wasn't that hard, only one trace had to be cut and three holes drilled per amp. 0,8 mm solid wire was used for that, to make it stand straight, when adjusting:
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At first, I tried it with only one amp on the left side, and it makes a huge difference, and gives possibility to tame it down. But even after that, the output isn't exactly 'crystal clean', as it has some 'grit' in it.
The overall sound, when tested on the thickest string, is quite dark(as it was before, when testing with thinner strings).
Meaning, that the lower frequencies are certainly there, but the 'definition' is missing.
Not sure, if it's just a nature of the optical components, or the amp circuit itself.
But here we go, instead of trying to get the maximum output, I'm getting interested of how the thing actually sounds.
AdeV:
--- Quote from: sorveltaja on January 03, 2020, 08:02:46 PM ---Pekka, thanks for the info. I was thinking of that envelope method, but the paper, where the transfers are printed, should be plain, instead of the magazine paper that has either text or images in it.
Glossy photopaper for laser printer could be a better candidate for that. Or some pcb-transfer specific product.
By using the uv-method, as the link provided tells, making two-sided pcb's could be a lot easier. Haven't got that far yet, when making pcb's. So indeed it would make a lengthy sideproject.
--- End quote ---
I did quite a bit of messing about trying to make my own PCBs last year.... I can summarise my results here (I'll do a proper write up someday):
1) UV exposure method is a right pain in the backside in a home shop. Getting the timings *just so*, and the exposure chemical strength *just so*, and then etching it just right - there are a LOT of variables. I reckon I must have used about 5 sheets of 100x160mm board, just to get one working 10x25mm board. And even that wasn't perfect.
2) Laser printer method is WAY easier. Forget the magazine paper, the laser printer will crinkle it, and it's hard to see the PCB print over the magazine print, especially if you're trying to go double-sided. Instead, use Vinyl (the sign-maker's type, that you cut in a machine). Works beautifully. I successfully transferred prints using a hot clothes iron, and latterly a slightly modded cheap laminator.
The only downside to laser transfer is pinholes - the laser doesn't cover 100% perfectly, so you can get pinholes in the traces. Not a big issue unless you've got very narrow traces. The upside is you just dunk the board straight into the acid after it's come out of the laminator. Have some acetone handy to wash away the toner once you're done.
Drilling PCBs is a whole different bag of fish. I bought one of those X-Y engravers, which works fine IF you get the boad perfectly lined up. Still working on that one... (well, will be, once I've got some spare time again).
Anyway - enough on that. I know it goes against the spirit of MadModder, but I think if I ever want a PCB that I *know* is going to work properly, I'll probably outsource it next time. PCBWay seems to get good reviews, and is cheap enough.
PekkaNF:
UV-method does needs some "dial" in. At the school we had repro camereras/films/pen plotters and all the works. Worked out fine. Secret was to use only fresh factory coated PCB:s and use two layers of film/paper that had darkest lines you could get and greatest UV pass trough you could get. Also the "envelope" had to be absolutely flat and UV-tubes have serious power.
I tried direct transfer method and I had best success with high coated high gloss paper, but applying just Goldilocks pressure/time/temperature turned out pretty difficult.
I have had some hit and miss success with UV-method, but my last try ended up to desperation, mainly because I had trouble with transparent material that would allow UV to pass. I bought the material that was confirmed to pass near 97% of that wave length....but I got the "improved batch" that was filtering about 99% of UV. Found out that when I made the "gradient" to find out, took like three minutes instead of usual 15 sec.
I have been thinking of routing method, but there is much CAM, indexing and all sorts of intricacies in that too.....
And then there is chemical copper and vias....
Probably best to buy board, but there is a definate apeal on "roll your own" .
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