Wouter,

Thanks for your comments.

The ICSP would be required to program the PIC on the HV side. The SMD ICs'
are soldered directly onto the PCB and
I use a small transition board that enables the Microchip ICD2 to plug in
via 5 way 2mm pitch header.
This also has a Schotky diode and resistor.

Then I would need crystal, caps for decoupling and crystal. An analogue
reference for the ADC inputs.
A voltage regulator with smoothing caps and suitable dropping resistors to
enable current for the PIC and
opto coupler. (Assuming I use a TX pin only). Then I need to have bit-bashed
code in the main processor
to receive the data. (Both UARTS are taken). I would also need a timer in
the main micro and interrupt
input to detect the start bit (time so that the micro can service the other
interrupts without too much disruption).

I could use the SPI bus but this would take more hardware interfacing.

To be able to probe the side that is reading the 3 x 230 VAC inputs and
converting to Digital, I would need an isolating
transformer for my scope.

So far from this thread, it seems the transformer option would be the
simplest solution and offer good isolation at the cost
of PCB area, but as Howard mentioned the clearance requirements for
isolation prevent the circuitry from being too close
anyway.

The 22mm x 22mm form factor x 3 will make layout a bit tight, I may need to
investigate stacking more PCBs and placing
the micro and other logic type circuitry on another board. Then leave all
the IO interface devices on the lower PCB near the
terminals and bring up the control signals via some DIL headers.

Thanks everyone for your input. I appreciate the variety of issues that have
been raised.

Regards

David

-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu]On Behalf
Of Wouter van Ooijen
Sent: Saturday, 30 July 2005 6:32 PM
To: 'Microcontroller discussion list - Public.'
Subject: RE: [OT] Circuit for measuring mains voltage


> Maybe another micro on the HV side could be added to do the
> conversion but
> this also needs a PSU,
> ICSP for programming and opto isolators.

You have a voltage on the HV side, so deriving 5V could be simple if you
can afford to dissipate some heat. The PIC would do just measurement and
sending the result, I see no real need for ICSP (compare it to an analog
solution: you must get that right first time too!).

I don't say this is the ideal solution, just compare it to other
solutions.

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: www.voti.nl/hvu


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