Hello all,

I've been struggling with a way to do a low cost isolated A/D ( <$2/
channel) for a PIC 16C877.  I need a total of 4 isolated inputs at 500V
of isolation with 8bits of resolution.  I've looked at a lot of
different possiblities, so far, a voltage to frequency converter coupled
through an optocoupler seems to be the most cost effective solution.
Then just count the pulses on a PIC pin in a fixed amount of time.
National semiconductors V/F LM331 is ~$1.50 and it's conversion is
linear.  I've also wondered if there was any op-amp configurations
(maybe Microchip's low cost op-amps) that might be cheaper than the
National's V/F and still linear.  I was considering powering each
channel with a flyback converter through a quad ethernet isolation
transformer.  I'm not sure if it would need a switching controller
(LTC1424-9 ~$2.90) or if I can simply send a buffered 1Mhz clock off my
CPLD.

Suggests welcome and appreciated.

Thanks in advance,

Todd Conard