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Old 21st August 2008, 01:26 AM   #1
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Default Optical Pickups

Arg, my electronics skill is so rusty!

This thread pops up once in a while. Has anyone tried anything recently?

I got a big bulky opto-interrupt that I want to try out as a prototype, but I can't even read schematics right anymore. I had to hook it up backwards from what I was reading to get it to change outputs when I interrupted it.

I have a ton of questions / things I need to think on. Anyone else interested in optical pickups?

What is a good range for output voltage and and output impedance for a guitar pickup?
How do I get the voltage down to a reasonable level?

I guess if I end up with way lower impedance than a magnetic pickup, that's fine right? I'm not attached to the purist guitar sound.

Why does this isolator look so noisy? Or is it my USB scope (parallax) being wonky?
Will other isolators be less noisy? Should I try discrete IR LEDs and photo-transistors/resistors?
Will the strings bang into the sensors if I strum hard? IS there enough room? Is this why it seems like only bass manufacturers make these?

Is there a good online electronics book going? I have a ton of books and text books, but none of them talk much about opto-isolators. This always happens!
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Old 1st September 2008, 03:57 AM   #2
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you are probably picking up ambient light with the opto, and that's your noise source. this is one reason there aren't any opto pickup designs on the market. the fact that the strings on a guitar must vibrate freely makes it nearly impossible to shield the opto from ambient light completely.
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Old 3rd September 2008, 09:06 AM   #3
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Quote:
Originally posted by unclejed613
this is one reason there aren't any opto pickup designs on the market.
Ummm, yes there is
http://www.lightwave-systems.com/

According to the magazines I've read on them, they have a blanket patent on the optical system too, shutting out all competition that uses *any* light waves acting as a guitar pickup.
(unverified info)

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Old 3rd September 2008, 11:21 AM   #4
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there's another company that has a blanket patent on any conceivable method of making an electric harmonica. and the company isn't making any, they just have a patent, and are probably just looking to make money in licensing fees. i call them "brainstorming" patents. Bell Labs did the same thing back in the 60's with a "brainstorming" patent on LED technology, and went after anybody who published any ideas about LED's that "infringed" on their patent. i think they eventually lost their lawsuits, since many characteristics of LEDs could be discovered by anybody "skilled in the art" (a phrase that is commonly used in patents, and should be carefully paid attention to...). if brainstorming is really patentable, then silicon solar cells and white LEDs were invented by Robert Heinlein back in the 40's, who even theorized the correct forward voltage drop...

actually in many cases "brainstorming" patents are just so much science fiction, since they assume advances in the technology in question that A, haven't happened yet, and B, can be figured out by anybody "skilled in the art".

i'm not a land shark, so i don't pretend to know a lot about patent law, but i have had a few patentable ideas over the years, and sometimes wish i had gone and patented them.
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Old 16th June 2014, 11:16 AM   #5
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What about using a laser light source of a determined wavelenght, along a laser photodetector?
AFAIK there are no natural random laser sources, so there shouldn't be any interference.
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Old 18th June 2014, 01:50 AM   #6
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I tinkered with optical pickups several years ago and gave up because of the ambient light issues. I haven't tried laser sources, but I have used IR remote control devices. The issues are similar. Even with optical filtering it is hard to make a detector that will respond to a small part of the optical spectrum. Even if you could do this, there are all sorts of random light sources throughout the IR, visible and UV spectrum. Stage lighting is a big one. TV sets, computer screens and other light sources are amplitude modulated with audio frequency noise, and those infernal CFL's emit a broadband light that is amplitude modulated with 60 Hz and high frequency hash.

I have had better luck tinkering with hall effect sensors and magnets. The 60 Hz pickup issue is similar to a conventional pickup, but the high frequency response is much better.
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Old 20th June 2014, 11:22 PM   #7
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Lightwave has actual products, and does license the technology to manufacturers, if you check out the site. They don't seem to be sitting on their patents. Optical pickups seem to appeal to a small, higher end crowd. That's been why you haven't heard of them. I'm surprised the patent hasn't expired yet. They've been around for awhile.
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