"I think you can do it cheaper and much more simple:
Tape the led together with an LDR
Use the LDR as the bottom resitor in a voltage divider.
Connect the divider to your stabalized 5V powersupply and the top of the LDR to your ADC.
Thats all !!! "

Very true ;-). And quite enough for Prahlad to loose his job ! I think he IS looking for ideas to implement in an industrial machine.

Robert, please don't mistake me - but the solution as you described will be "perfect" for a home brewn setup. And even here, if you don't use a X2 / flame retardent capacitor to apply across mains - safety is compromised.

Reason why I am pointing out this : There are many students who visit this forum and dabbling in 230V mains, based on such tips could prove to be an unpleasent experience.


Raghu