> > Josh Koffman wrote:
> >> I had initially considered trying to find a digital pot or
something
> >> that would allow me to vary the resistance. I didn't end up going
> this
> >> route because I was worried about impedances and I wasn't sure if
I'd
> >> have to add buffering to the signals.
> 
> Olin replied:
> > This may not be applicable to your situation, but a long time ago I
> did a
> > "electronic volume control" circuit using LEDs and CdS cells.
> 
> Yes. An entirely practical solution.
> CdS sensors are still available (I bought some within the last year)
> BUT ROHS may frown on the Cadmium content.
> Various photo transistors may be used in the same manner.
> Even an optocoupler may be usable.

You can get optocouplers that use an FET rather than a bipolar
transistor. I don't know how linear the transfer function would be in
this instance, but probably worth investigating.
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