Isaac Marino Bavaresco wrote:
> Em 12/9/2011 10:34, Michael Watterson escreveu:
>  =20
>> Forrest Christian wrote:
>>    =20
>>> I'm struggling with coming up with a circuit which I actually like for=
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>>> measuring AC line voltage and current.   The goal is to be able to read=
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>>> the voltage of AC line within a volt or two within a microchip PIC.... =
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>>> For obvious reasons I'd like something where in normal operation the AC=
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>>> line is isolated from the PIC side of the circuit.
>>>  =20
>>>      =20
>> Neon and a photo transistor? Should work at about 200uA on  mains side?
>> Voltage varies the current thus brightness due to large series resistor.=
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>> Better suited maybe to 230V AC than 110V AC.
>>
>> Hall effect sensor to measure line current.
>>    =20
>
>
> It seems that my suggestion got lost in the list:
>
> "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."
>
>
> Isaac
>
>  =20
I thought that a good idea. But I thought he objected to current draw of=20
the LED in the coupler? Can you go less than 1mA?

However ADI has isolated RS422/RS485/Can transeivers.  But I  don't know=20
what  PSU draw is.

A PIC  (100uA to 200uA  via  capacitive dropper?)  feeding  serial data=20
via small cheap pulse transformer or opto-coupler.

I once used a Quad DIL pulse transformer for isolated Analogue I/O
1) 500KHz for powering CPU and Opamps etc.
2) Data clock
3) Data in
4) Data out
CPU was a NEC 78HC11 with internal shift register parallel load/unload.
So host read "last response" while clocking in new command.


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