I'm struggling with coming up with a circuit which I actually like for=20
measuring AC line voltage and current.   The goal is to be able to read=20
the voltage of AC line within a volt or two within a microchip PIC....  =20
For obvious reasons I'd like something where in normal operation the AC=20
line is isolated from the PIC side of the circuit.

The obvious brute force way is to use a transformer.  Unfortunately=20
brute is pretty much the way to describe this - big and heavy, even at=20
1.5x1.5x1 inches.  Especially since I really need to monitor two sources=20
at the same time. Although it definitely works.

I'd really like to do something more 'electronic' - I.E. smaller and=20
lighter.   Unfortunately everything I am coming up with involves drawing=20
at least 5-6mA from the AC line for things like driving the emitter on=20
an optocoupler, plus circuitry for the optocoupler, including power=20
supplies for such things as opamps or processors with ADC's  - which=20
quickly equates to at least a half of a watt worth of current @ 120V,=20
and often quite a bit more.   Which is a lot of heat for me to get rid=20
of - I really don't want a heatsink, and I'd really like to be able to=20
do this on the bottom of the board where it's hidden from wandering=20
fingers, but unfortunately also where there isn't a lot of opportunity=20
for heat to dissipate due to the confined space.

I keep hoping to come across a really teency isolation transformer or=20
similar, and/or a simple, clean circuit that does what I need it to...=20
But alas, after hours and hours of looking, I'm no closer.

I'm hoping someone can give me a hint as to what I might want to be=20
looking for.

-forrest






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