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Diy optical pickup for guitar -- is it possible?
sorveltaja:
After some testing with current electrical setup on the breadboard, it could be worth of building. The circuits are very simple, but when there are six of them, using perfboard, it is way too easy to make mistakes.
So I'm going to make the actual pcb(s). Bit of an extra work, but the resulting board should be a breeze to populate.
The only thing, that has changed since I made pcb's years ago, is the laser printer. Hopefully its ink has similar properties, as the previous printer.
As always, there is only one way to go where no man has gone before find out.
In the past, I used cheapo transfer method, where the pcb pattern was printed to gloss or semi-gloss magazine/ad paper, then transferred to the copper surface of the pcb.
Results weren't 100% perfect, but in most cases, that was more than enough.
sorveltaja:
Making the pcb went just fine, but only after etching, I noticed that it was a mirrored version of the circuit
But that aside, the first pcb consists only the amplifier stage for the phototransistor, in hopes of keeping the overall construction 'modular':
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After testing, that the above pcb works as expected, the first candidate for the next 'module' is one, that consist of 4093 ic's, with schmitt trigger configuration.
What I mean by 'modular', is that the amplifier stage isn't permanently tied to any of the following whatever-stages, so if one doesn't work, take it out and replace it with something else.
sorveltaja:
The first pcb is ready to go for testing. For me, the drilling is always the most thrilling part.
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Babbling:
Thin carbide drills are usually very fragile, and are to be rotated at high speed. Not so in this case, as I used about 2800 rpm(max rpm of my mill) for the 1mm one.
As a precaution, the drill's vertical movement was minimised, so that it just penetrated the pcb.
One might ask: why not use hss drills instead, as they are dirt cheap, and more flexible?
Anyone, that have used hss drills for pcb's, knows, that after 50 holes they are as dull as it gets, and tear instead of cutting.
Although carbide drills cost a bit more, and are not to be used for hand-operated drilling(ask me how I know), they don't wear out easily.
Some kind of (lightweight will do) drill press is required, though.
Reason for this run out? If there are newcomers reading this thread, willing to make their own pcb's, hopefully they get more info to get over the learning curve involved, than I had in the past..
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But enough of that. Drilled pcb as it is:
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sorveltaja:
There was an error in the previous pcb, but it's now fixed:
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It's just a bare bone circuit, which could be cropped even more, by replacing upper right 10u capacitor with a jumper, as I'm not sure if it's needed at all.
Although it's working as expected, it seems to need some kind of psu filtering thingamabob to suppress overall noise. I use a simple one like this, which could also be used as a split power supply.
It was used only to power the amplifier circuit, and not the power hungry ir-leds:
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So far the testings and adjustments were done by using scope, function generator, and multimeter. But they don't reveal all. The end result is still judged by aural testing.
Next stage after the amplifier could be a schmitt trigger, zero cross detector, or about anything, that is able to clip the output to suit cmos ic's.
sorveltaja:
Simple zero cross detector(zcd) from datasheet..
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..and 4093-based schmitt trigger were compared as signal 'squarers'.
Zcd did work, but its sensitivity(or lack of it) made it to cut the signal from the plucked string too early. Another version, that has 10mV sensitivity, although having more parts involved, could still be an option to test. With that high sensitivity, noise could be a problem, though.
Zcd with an adjustable/variable input sensitivity would be jolly good to have in this case. But when searching on the net information about it, such things doesn't seem to exist.
Then there was the 4093-based schmitt trigger, which did let the signal from the plucked string to 'squarify' bit longer, making it to look more 'natural' response.
Current circuit has (maybe)enough amplification for the receiving phototransistor. On a second thinnest string(0,33mm/0,013"), when plucked, the output goes to 9 volt(with 9V supply), and fades as the string vibration decreases.
So the circuit is pretty much same, as it was previously:
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