>
> 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.

I haven't done the full costs but my first reaction would be to do the
A2D on the isolated side with a chip like the MAX1111 and optocouple
the serial interface. Power would be via an isolated capacitor drive
(cheapest method) and since the I.C. only draws 6uA@1kS/S and 85uA at
50 kS/S the 1 MHz drive wouldn't have to be too grunty.
Its also single supply and costsUS $1.69 (last 1000up price I have)
_____________________________

Lance Allen
Technical Officer
Uni of Auckland
Psych Dept
New Zealand
_____________________________