voltage sensing

Hi. I was wondering if someone has ever constructed a Switch Mode Power Supply using isolated voltage and current sensors connected to a Microcontroller. If so: What device (Voltage/Current) have you used and using what protocol ( i2C / SPI etc ) ? What sampling rate could be achieved ( 200kHz+...

I need a circuit to flash an LED. The battery is 3.6v 1A, this powers a fairly dim 2.5v micro LED (probably a very low current), I don't think this alone could power a flashing LED circuit, so I want to piggyback off of this LED to trigger the circuit to flash a 3.6v LED. So I'll have a 3.6v...