>> So if you'd like to provide comment on my interface >> circuit, have a look: >> > > > > Seeing that you've gone to the effort of including TR1 - > could it's output be used for voltage sensing, making the > whole electronic system 'potentially' low voltage? Phase > shift of voltage WRT current waveform is crucial for power > measurement so you would need to ensure that the electronics > power load preserved this. > What's the purpose of IC2? It looks like the first stage is just a non-inverting amplifier. The second state appears to add a positive offset to center the sample in the ADC range. Could you not get a similar effect by just having the terminated current transformer primary driving the left side of R12 and biasing the other end of the transformer up to Vcc/2? You can probably adjust the transformer terminating resistor to get the peak to peak voltage to match the range of the ADC. The voltage sense circuit appears to take the average of ACA and ACB, then attenuate it. Ideally it would be (ACA-ACB)/k instead of (ACA+ACB)/k. I agree that it would be nice to use the power transformer for the voltage sense. Is the center tap of the secondary of TR1 grounded? Without that, I don't think you can guarantee that ground will be centered between Vcc and Vee. On using the power transformer for voltage sensing, it does, of course, need a grounded center tap. Also, the transformer may need to be oversized somewhat to prevent distortion of the waveform when the diodes conduct. You might also want to use a 230V primary transformer with double the secondary voltage so you are a long way from core saturation. As primary voltage goes up, secondary voltage will not follow in proportion as you approach saturation. If you go with the transformer for voltage measurement, it would be interesting to do a primary to secondary voltage ratio measurement over a range of voltages. Harold -- FCC Rules Updated Daily at http://www.hallikainen.com - Advertising opportunities available! -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist