Hi,
I like Mr Doug's Idea as its the cheapest and would save quite some space
required by the transformer. I could just rectify the AC Voltage and then
use a
resistive divider to scale the voltage down to say 3 volts. But i'll have to
add a
couple of Mica Capacitors of say 0.47mfd/300 Volts to flatten out the DC.
And after
the Voltage Divider, I might also put up a small LC network based Low Pass
Filter.
And finally, a Kamikaze Zener Diode of say 5.2 Volts to Commit Suicide and
Protect
the PIC if one of the Divider resistors is to fail.

So, the voltage I'll be getting will be the peak voltage. How do I get the
RMS Voltage ?
Any ready made algorithms on PICList would be great.

And finally, anyone's got any comments on this design ?

Jeethu Rao
www.jeethurao.com

-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Douglas Butler
Sent: Friday, June 22, 2001 7:06 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC]: Reading Mains Voltage From a PIC


If you rectify the 230VAC first you can use a very non-perfect
rectifier.  The errors will be insignificant vs. the 300VDC result.
Then use a resistive divider to reduce the 300V to 5V for the PIC A/D.

The will give you the average voltage level.  If you are looking for
single cycle dropouts you will have to do something faster, probably
synchronized to the power line frequency.

Do you need to isolate the PIC ground from the AC mains?

Sherpa Doug

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