Moving conversation from IoTaWatt 4.0 Thread to here : IotaWatt 4.0 - #97 by overeasy
I plan to give it a try and see how it goes when all the parts arrive.
The basic idea is using an op-amp to do a differential to single ended conversion. I am also a bit skeptical as I still don’t fully understand how it overcomes the problem you described, as there is still a point where we attach a kind of bias to the AC in the positive input of the op-amp, but apparently with the high impedance between the circuits and the filtering basically offered by the power circuit it eliminates problems. I am sourcing parts now and drawing it up properly.
If it works out, I will certainly post it up. Actually I might post it up once I have completed drawing anyway and see if anyone has feedback.
As also mentioned, there will be problems of loading on the transformer causing distortion in my measurements. Again, I plan to use a few tests to try and quantify the impact of that distortion and see if there is some software solution to model it and filter it out. I have not done my research on this yet, but I think I may need another inline on PCB current measure for the AC line to be able to more accurately model the impact on the 9V AC transformer as I draw more load.
My plan is to get everything I need to build standard IoTaWatt 4.0, and also buy bits to experiment on a breadboard. If my experiments fail, then I have all I need to produce something that is known to work so its not a complete loss and hopefully I learn something in the process.