SparkFun Forums

[kycaver]

Hello,

I'm trying to build a light sensitive theremin using the instructions found at:
http://www.oocities.org/soho/lofts/8713 ... remin.html

I'm not having much success. I'm using a breadboard. My speakers register current, but nothing from the rest of the unit. I realize this is not much information. But at this point, I'll take any recommendation on what I can/should do to move forward with troubleshooting.

Thanks,
Mark

[Mee_n_Mac]

My speakers register current, but nothing from the rest of the unit.

I don't understand what you mean by the above. The circuit is an oscillator whose frequency should vary with the resistance of the photocell. According to the article the value of the cap was originally 0.01uF, not the 0.1uF shown. It could be the frequency of the oscillator is too low for your speaker. Try reducing the value of the cap to 0.05u or 0.01u.

What photocell did you use ? They do vary and the one SFE sells may be different in it's range of resistance from the one used waaaay back when. You might try a resistor in place of the photocell, values ranging from 1k, 10k, 50k, 100k.

[Mee_n_Mac]

What photocell did you use ? They do vary and the one SFE sells may be different in it's range of resistance from the one used waaaay back when. You might try a resistor in place of the photocell, values ranging from 1k, 10k, 50k, 100k.

I'm quoting myself because I simulated the circuit and I couldn't get it to oscillate until the photocell resistance was 50k or larger (C = 0.1u). The PC SFE sells will quite likely not work.

[jremington]

CDS cells usually have megohms of resistance in complete darkness (down to a few hundred ohms in bright sunlight), so try the circuit out in a dark room, then gradually admit light. That circuit should work!