Linear response VCA's

[KA4HJH]

>I "borrowed" the DAC from another system, and priced it later - oops!
>$22.00 ea. It seems that a 16-bit parallel DAC capable of near-DC will cost
>at least $15.00. I think that's overkill for the application.
>
>So I'm working on alternatives - will probably spend the next couple of
>weeks playing with things: semi-discrete DACs, PWM techniques, switched
>integrators, etc.

You already have an MCU, just mulitplex the DAC! For this application you
should be able to support 8, 16 or even 32 channels! For an example, check
out the MIDI gadgets at Midwest Analog Products (where's that url?). They
have schematics and source code for the whole thing.

Or you could use a smaller DAC and voltage-control current sources/sinks
connected to capacitors, which would eliminate the zipper effect.

Terry Bowman, KA4HJH
"The Mac Doctor"