Low cost isolated A/D

1.  Each of the four inputs needs isolation from each other.
2.  It can be a very slow conversion and only one at a time is necessary.
3.  It only needs to be 8 bits.
4.  The isolation barier only needs to be 500V.

Has anybody looked at sending power and signal through a high voltage cap.?
Linear Tech. had an interesting app. note where they sent power to an A/D and
recieved data back from it through the same transformer.

Thanks,

Todd Conard


Mike Harrison wrote:

> On Mon, 23 Aug 1999 19:57:35 +1200, you wrote:
>
> >+AD4- I've been struggling with a way to do a low cost isolated A/D
> > +ADwAJA-2/
> >+AD4- channel) for a PIC 16C877.  I need a total of 4 isolated inputs at
> >500V
> >+AD4- of isolation with 8bits of resolution.  I've looked at a lot of
> >+AD4- different possibilities, so far, a voltage to frequency converter
> >coupled
> >+AD4- through an optocoupler seems to be the most cost effective solution.
> >
> Does each input need isolating from the other ? If not how about a
> 12C671 on the hot side sending async serial data through an
> optoisolator ?