Yeah, go to Allegromicro.com and pick up some of their current sensing
chips.


Shawn Wilton
Junior in CpE
MicroBiologist

Phone: (503) 881-2707
Email: shawn@black9.net

http://black9.net


Ian McLean wrote:
> Hi all,
>
> Could someone point me somewhere or give some advice on monitoring 240VAC
> 50Hz mains voltage using PIC A/D.
>
> The reason I wish to do this is to display the output of a variac on an LCD
> panel.
>
> Immediate methods that come to mind are:
> a) Step down the mains with a step down transformer, rectify the output,
> filter, and resistive voltage divider.
> b) Leave the step down transformer out of the equation, and use higher
> voltage rated filter caps, and a bigger resistor divider.
>
> Both the above methods could empoy a level of PIC protection by using an
> op-amp configured as a voltage follower with no gain to clip the output to
> the AD 5V rail limit.  I figure both methods should give a reasonably enough
> linear output.
>
> I can see problems with both of these methods however, particularly in
> regards to ground rail impedance caused by the high voltage divider, esp. in
> option(b), and causing major headaches for the low voltage ground reference
> side for the digital electronics.  Can anyone suggest a better way ?
>
> Hmmm.  Maybe I should have just stuck with the simple moving iron meters ;)
>
> Regards,
> Ian
>
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