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Do they make opto-interrupters with diode outputs?

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low affect

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I can only find the transistor output kind. I don't want to have to power the output side (besides what current what the LED causes)

Do you guys know a good place to look for opto-interrupters beside digikey and mouser? I'm trying to try out a bunch of different kinds.
 
If you don't want to power the output side you might as well forget about an optocoupler.

It's main purpose is to isolate two circuits one from each other.

So, no, there isn't any optocoupler with diode output.

Boncuk
 
You could use the CB junction on the transistor side, but the current is VERY small. Light bulb and solar cell? Transformer, rectifier and cap? ;) How much power do you need on the output?
 
You could build one with a pair of LED's in a brass tube, I've gotten over a volt this way. But, the power level is vanishingly small - microwatts. You aren't going to power anything with it. What is your application?
 
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Solid State Relay

If you don't want to power the output side you might as well forget about an optocoupler.

It's main purpose is to isolate two circuits one from each other.

So, no, there isn't any optocoupler with diode output.

Boncuk

Here is what I made when I needed a solid state "relay". Input is by nature insulated from the output.

Solid state relay. (Low Power) photo - Rolf photos at pbase.com

This was designed for use in a RF remote trigger for a digital camera. It has now been resurrected for use on a much newer camera.

The green LED was filed flat and the Cds glued on with instant glue. Then it was covered with black heat shrink tubing. If you wonder why a green LED, it was evedently the best light spectrum for the Cds. Other colors did not give as low an output resistance.
 
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Are you trying to isolate the pickup signal from the amp, or detect the string vibration? A "normal" opto-isolator is very non-linear.
 
Detect string vibration. I know discrete emitter/detector would probably sound better, but the packaging of an opto-isolator is really convenient. Here's a little schematic I scratched out with components I could find on my desk.

**broken link removed**
 
That looks fine. I don't understand about not powering the output - you already have power for the LED, why don't you want to use the same power source for the output transistor?
 
Just to save a little power consumption I guess.

I try to position the string so that when it's not moving, the transistor is biased right in the middle. I've only tried this with a thick string; uh oh, I hope it works the same with a really thin string too.

And aren't diodes a little faster?

I'm trying to keep the circuit as simple as possible.
 
PIN diodes are faster, yes, but the transistor types are plenty fast for audio. I would be more concerned with nonlinearity and device-to-device variance.

The power consumption of the output should only be a small fraction of the LED. What size resistor are you using on that collector? It should be considerably bigger than the 150 ohm led resistor. A gain stage wouldn't hurt, you can get an opamp that draws less than a couple of milliamps, will amplify that signal and lower the output impedance to reduce noise. 910k is pretty high, could pick up hum.
 
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Looks like ~9K ohm on the collector.

If I find a bigger cap, and go for an output impedance around 150 Ohms, is that going to screw anything up?

What should the collector resistor be? I might have calculated something to get that value, or I might have just guessed...

It's been a long time since I've done any electronics; my transistor-fu is really really rusty.

Here's a little article I found on output impedances. I don't think my impedance will vary with frequency, since this isn't a magnetic pickup. Maybe I should go with an output impedance around 3K. I should test all this out to see how it sounds before I go building 6 of them...

Thanks!
The output impedance of most professional microphones is low, generally in the range of 150•, so mic preamps should have an input impedance of about 1,500• or 1.5 kilo-ohms (k•). (Some mic preamps have an input impedance as high as 10 k•, but the range from 1.5 to 3 k• is more typical.) Line-level devices, such as synths, also exhibit low output impedances in the 50 to 100• range, and they operate well with any input impedance more than 1 k•. Older synths and some consumer hi-fi equipment often have output impedances in the 100• to 1 k• range, which requires the destination device to have an input impedance in the 1 to 10 k• range.

An electric guitar's output impedance depends on the pickup design, the settings of the volume and tone controls, and the frequency produced. When the volume knob is turned up (which is usually the case), the guitar's output impedance is typically 3 to 10 k• at low frequencies and 100 to 500 k• at 10 kHz. When the volume is down, the output impedance is more constant, but it still varies by a factor of ten from low to high frequencies.
 
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9k is fine, it's drawing like 1/60th the current of the LED - not enough to be concerned with if battery drain is the issue.

If you have it midpoint biased the way you said, you have the right value for the collector resistor.

A bigger cap would be good, but don't try to lower that output resistor to 150 ohms without a gain stage, it will load down the opto transistor. When you start to combine the outputs (sounds like one opto per string) an opamp would be a big help because each string output would be heading for a summing junction with a series resistance of like 100k or so.

I think this is fine for now, unless there's some other problem than your power concern. You probably have bigger issues with the optics and mounting and alignment and all that, lowering the output impedance can wait.
 
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