You could make a circuit with a small PIC (8 pins) with A/D converter,
connected directly to the AC line, powered by a transformerless power
supply and using a resistive divider to measure the line voltage. Then
transmit the result of the measurement to the other side of an
opto-coupler to a circuit that implement the remaining functionalities
of your appliance.

This way you can read as many different signals as you wish.


Best regards,

Isaac



Em 11/9/2011 00:17, Forrest Christian escreveu:
> 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
>
>
>
>
>
>

--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.