OpenEnergyMonitor

Hey, sorry I misunderstood/misread your first question, you were referring to the voltage measurement part of the circuit right?

Thanks for the link to schematic and app note I had a read through and studied a couple of other app notes as well, they all as far as I can tell seem to be using half-wave rectifier circuits for the power supply which if I''ve understood correctly allow's it to be a grounded supply.  The power supply circuit that I'm using uses a bridge rectifier which means that it is floating or ungrounded. I think maybe I'm wrong in trying to use a bridge rectifier circuit instead of a half wave power supply circuit and this is probably the source of the interference I mention above, so thanks for pointing out the app notes.

Here's the LTspice circuit for the voltage measurement and power supply circuit above,  it seems to give a near-sinusoidal voltage output: Vmeasurement.tar.gz 

and here's the LTspice circuit for the half wave rectifier circuit that you linked to with the ac coupling capacitor, it also seems to give a sinusoidal output but maybe a bit better than the bridge rectifier circuit: halfwave.tar.gz

So I think I will try the half wave power supply for the next version of this circuit with the ac coupling capacitor, although the current version does seem to work: the real power, power factor and apparent power measurements seem to compare well with the values I read off the plug meter.

In your last post you mention needing a series cap on the adc input, is that in the same way as the ac coupling capacitor with the voltage divider after it? a series cap direct to the adc input without the biasing voltage divider wouldn't work as it would remove the dc bias, right?

Thanks for raising the questions about the circuit, I think I have learnt a bit more from them, and will post up the results of the half wave power supply circuit as soon as I get a chance to build it.