I posted a question earlier,
How to measure AC voltage without a voltage divider using microcontroller
and I got some very useful answers, one of those was to implement this for isolation
http://www.edn.com/design/test-and-measurement/4344950/Optocoupler-simplifies-power-line-monitoring
I am having trouble understanding the circuit in the link above, so I need a help.
I dont understand why is a 3.3V reference used here at both the isolated and non isolated side of the circuit? The 5V is for the opamp which I totally get but why 3.3V and also with what ratio should R1 be changed to cater 220VAC? How are the gain values calculated here?