[sdiy] Three Leg Photocell Hunt

[Tim Parkhurst]

On Tue, Mar 30, 2010 at 12:09 PM, Kyle Stephens <lightburnx at yahoo.com> wrote:
> Ahoy...
>
> I'm looking for a three terminal photocell with potentiometeric response (the exact log/linearity isn't important) - like what's in a three legged Vactrol.
>

You might try one of these:
http://www.alliedelec.com/search/productdetail.aspx?SKU=6990036
It is listed as a "Dual Output Optocoupler" (part NSL-33SR7/2) so it
might do what you're looking for. It's a bit pricey though. This is a
Silonex part, so you might check their web site too
http://www.silonex.com/audiohm/index.html
(although the device listed above is curiously missing from their
product listing).

The trick though, is that to simulate a pot being used as a voltage
divider, you'll want two photocells with one going up in resistance
while the other goes down. I can't see how this would work with both
cells in a single package. You might be able to get the proper
response by using two photocells, and driving one with an inverted
copy of the LED control voltage.

Tim (driven with an inverted copy of reality) Servo
-- 
"Sire, the church of God is an anvil that has worn out many hammers."
- H.L. Hastings