CdS/photoresistor mod

edited May 2009 in WTPA1 Mods
This is a question for Todd or anyone else who's already up and running and fiddling-
My kit hasn't arrived yet, but I'm already exciting about modding it once it's done. Can you think of anyplace where a CdS/Photoresistor cell placement could be put to especially juicy effect?
Cuz Electronics Goldmine is having a special on bulk cells
a smaller assortment here
I figure if you have 100+ of them you should use them everywhere (which probably only sounds good in theory)


  • You could build a simple Schmitt trigger oscillator with the resistive element being the photocell (with a range and offset pot maybe), and run that in as the external clock source.

    Do some parallel resistor calculations and hook it up to the level out pot (or any other realtime peramter), and you got a VCA of sorts...

    Good ol' bending too, just get some leads n start poking.
  • As an addendum, there's a perfect circuit here, sans the S&H chip:

    As called for by Todd, it's a stiff, regulated 5 volts, just what you need for the clock signal.
  • Hey andidilu--
    Depending on what you're going for and how much you want your device to act crazy, you can replace or parallel those CDS cells in with lots of different things in the circuit. The big thing to remember is the impedance of the photocell. IIRC the "dark resistance" is pretty high -- almost always over 100k and usually over 1M, and the "fully illuminated" resistance of those guys is not much less than 10k usually. This means that you could use them to make direct replacements for any 118k resistor on the PCB, including the ones in the DAC. That would sound totally crazy. Do that and tell me how it sounds.
    You could also run one in parallel with the coarse oscillator adjustment, which would make a significant difference in sampling frequency. The fine pot is too small of a value.
    You could remove the paralleled 59k resistor from the 500kA pot on the output amp and parallel the CdS cell and you'd probably get some pretty fierce clipping. Might be cool. Same for the input amp's 500kA pot. That's where I'd start, I think.

    erschlagener's advice is spot on, too.

    Hope this helps!

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