I'm designing a power meter, because I don't like the design of the enerjar (enerjar.net), and I just wanted to design my own. I'm working on the interface which is what mainly interests me. The PIC/AVR/HC11 will be the pretty standard MCU+16x2 LCD + bluetooth module (no contact.) So if you'd like to provide comment on my interface circuit, have a look: I like to think the voltage sensing circuit is semi-intelligent. In normal households (in the USA here) the ground + neutral is bonded at the distribution panel. One wire is 'hot.' The voltage divider will output a value if either wire is hot - it doesn't matter which one. Voltage drop over the neutral wire shouldn't (I think) affect the accuracy. It uses a 1:100 current transformer for current measurement so I don't need any AC referenced shunts. So this part of the circuit also doesn't care which wire is actually the hot one. Goals of the circuit: 1. Accuracy 2. Use of easily available parts (though I'll probably use something better than the '72 opamp) 3. Relatively simple (two ICs, resistors, capacitors, diodes) 4. Relatively safe - yes it's connected to the AC line but at least it's ground referenced. A 1Meg resistor would allow up to 170uA to flow - probably safe enough (?) It's not intended to be galvanically connected to anything or anyone. So I just drew up the schematic in the past hour. I reserve the right to have made a huge mistake. - Martin Klingensmith -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist