I partially got my previous dimmer circuit working. I was able to get the CPU to power up, run programs and do transmit/receive via the radio. However, my circuit to measure the current through and the voltage across the load did not work. The Op-amps I selected did not have a high enough common mode voltage rejection ratio to prevent them from locking. To solve this problem, I have switched to the LM2902 which has six times the common mode voltage rejection ratio of the LMV356 used in the previous design.

Here is the current design.

Before I submit my layout for this circuit to the PCB manufacturer, I thought is wise to give it a try. Below are a couple pictures of the setup. The trick to this circuit, as mentioned above, is to use an Op-amp with high common mode rejection. Also, it is important to float the entire circuit to a common ground. In the real circuit, powered by the AC input, this is no problem. Everything is referenced to Neutral. On the bench, I was using my bench supply for the DC voltage supply and a separate AC voltage supply for the signal. To get them referenced to the same ground, I tied the DC ground to the Neutral of the AC voltage supply. Works great!

Setup. This is a picture of the current and voltage sensors. The virtual ground is also included. The three brown cylinders on the left are my dummy load (300 ohms, 50 Watts). The AC Live line comes in the top of the board on the green clip-cable and goes out the bottom of the board on the orange clip-cable. The signal goes through the dummy load and returns on the black clip-cable. At this point, the signal goes through the sense resistors (the large blue resistors in the middle fo the board - 2x .250 Ohm at 3W each). It then returns to the AC supply via the brown cable going out the top of the board.

Circuit. In this picture you can see the two sense resistors in series with the Neutral side of the AC supply. The bottom left Op-amp (pins 1 - 3) is the current sense circuit. The bottom right Op-amp (pins 5 - 7) is the voltage reference and the top left Op-amp is the voltage sense circuit.