Quote Originally Posted by Atom058
Bill - Thanks for your reply. I searched a little through the Elektor Forum and was not able to find anything like what you were describing. Can you point me in the right direction? Also, after looking at the spec sheet for the LM331, can you tell me if the circuit that they have diagrammed is necessary in it's entirety? Did you have a simpler design?

Thanks! Atom058
It was in a print edition in late 80s - let me see if I can find it in the archive and scan it. It was a mains voltage monitor in UK Elektor.

The Circuit I used actually had the Maxim MX636 (I incorrectly mentioned NSC before) version of the AD636 (I used it because it was part of the free samples that were available at the time.) I used transformers for isolation as I didn't want to blow up the PIC, the computer, or myself !

Not sure of the merit of converting voltage to frequency rather than just doing an RMS measurement in either hardware or software after stepping the voltage down. Have a look at Circuit Celler a while back - Jeff Bachiette (sp?) did an article using the Alegro current sensors where he did some RMS measurements in software to work out the peak current at the peak of the mains cycle - it might help. He did it in a 12f873 using PBP. Let me go out to the shed and see if I can find the article. The code should be on the CC site.

Bill.