Ask an analog question in a digital group...!

Assuming there's power on both sides of the circuit, use an opamp on one
side to light the LED inside the optocoupler.  The brightness will
depend on the current flow, which will depend on the output of the
opamp, which will depend on the signal.

On the transistor side, measure the current flowing through the
transistor in the optocoupler.  Use an opamp to buffer it and convert it
back to a voltage.

Pick the correct values for the opamp gains and the voltage out will
equal the voltage in over the entire range.  Pick the correct opto and
opamps and you will get all the bandwidth you could ever use.

Maximum of one tiny opamp on each side, an opto, and maybe 5-10 passive
parts.  Bonus points if you use transistors instead of opamps, since
they'll be vastly cheaper and an opamp is overkill for this application

There are some great circuits that do exactly what you need in this data
sheet:
http://literature.agilent.com/litweb/pdf/5988-4104EN.pdf

Hope this helps!

-Adam

Jinx wrote:

>Any suggestions/recommendations for opto-coupling a DC or low frequency
>signal (10s of Hz) to the AN pins for measurement ? Maybe V-F -> F-V for
>example ? Pointers to a proven design would be absolutely spiffing
>
>TIA
>
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