Hi,
I'm having some difficulties with a circuit to measure more than one mains voltage inputs.
Attached is a simplified circuit diagram of what I am trying to achieve.
There is a fly-back switch mode power supply to generate the 5V for the micro-controller and power other parts of the circuit (not shown).
The incoming mains voltage is divided down with resistive divider and passed through RC filter, buffered and input to ADC of micro-controller to read an average AC mains voltage, this section of the circuitry works fine.
The lower part of the circuit is to read a variable AC mains control voltage. The voltage is divided down and passed through RC filter, buffered and input to micro-controller as above. There is something going on that I can't get my head around just yet which I believe is related to the single ground point for the 2 rectified inputs. When observing output of the second bridge rectifier only one half cycle is varying as the the variac is turned, the other half cycle is always maximum (see scope screen shot attached).
Any advice on how to correct problem with current circuit or alternative circuit much appreciated.
Dean.