[sdiy] photo resistor as CV source

[Ken Stone]

+15
|
R1 resistor
|
PR (photo resistor)
|
+----out
|
|
R2 resistor = R1 + PR(dark)
|
|
-15V

you may need a resistor across the photocell too, say 470k. R1 would be
100k, and R2 would be 560k-680k - perhaps a 1M trimmer to zero it out.

Ken

>hi all, 
>i'm trying to use a photo resistor as a CV source for
>my -/+15 Volt modular synth. the circuit i made is
>just a >2 Meg photo resistor in series with 2 9 Volt
>batteries (18 Volts), with a jack coming off. it works
>from about 8 Volts up to 18 Volts, but i can't get it
>down to 0 Volts. I tried putting a potentiometer
>inline and that lowered it, but not enough. i know i'm
>missing something simple probably. can anyone give me
>ideas or point me in the direction of a schematic?
>thanks very much!
>Daryl
>
>
>
>		
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_______________________________________________________________________
Ken Stone   sasami at hotkey.net.au or sasami at cgs.synth.net
Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/>
Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>