At 11:44 AM 3/20/2010, Russell McMahon wrote: >There seems to be a reluctance to even consider the suggestion I made. >It may have been commented on an rejected for some good reason but I >don't recall seeing it. >Transformer and 2 resistors in basic form. >Connect one leg to Vdd, other via divider to ground and tap to ADC in. >Add cap if desired for noise handling. I suspect there have been no comments for a couple of reasons: 1) One of the schematics that Dario posted shows another signal tapped off the transformer signal and going to somewhere marked "dimmer". I assume that signal needs to be ground-referenced. 2) I don't think that your approach works as you envision it. I *think* that Dario mentioned that the transformer has a 12Vac winding. That means peak voltage is about plus minus 17V. Put that in series with the 5V rail: that gives voltage range of +22V through -12V. Doesn't matter what your divider is, you are still going to see the voltage go below ground. You would need to add another resistor from Vdd to the divider tap. That's pretty much what Olin suggested (although he also AC-coupled the signal). dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist