Bruce Douglas wrote: > There is an interesting circuit at > http://www.circuitcellar.com/pastissues/articles/May96/text.htm which > uses 2 pairs of optoisolators to read the current. As far as I could > tell, his firmware does a simple multiplication of voltage times current > so wouldn't be good for reactive loads. No, it does the multiplication in the analog domain in real time, so it correctly handles reactive loads. The A/D converter is measuring the net real power. The original reference for the power-measuring circuit is: W.S. Woodward, "Optical isolator computes watts," Electronic Design, 102-103, October 14, 1994. This circuit is not suitable if the OP wants to measure voltage and current separately and calculate power factor, etc. -- Dave Tweed -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist