Forrest W Christian wrote:
> Don't these all require a separately-derived power supply on the 
> measurement side?

Not if the voltage is about a volt or more(an IR LED drop). Opto #1 LED
sees the measured side. Basically the output of the two optos fight it
out for the opamp's input - the opamp drives opto #2 LED.

There are examples on the web, many from opto makers that supply matched
pairs. Russell was suggesting doing your own matching, I think.

Cheerful regards,

Bob
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