signal transformation

[hapetter]

Hi.
I'm making a frequence measurement sensor.
The application is:
Measure frequency from potensial transformer of a generator.
The signal is 0-220VAC, 0-120HZ.
I need to transform this sine AC signal into a signal read by a comparator. The comparator will make a square wave. The transformed signal will be read by an AVR microcontroller for frequency calculations. The microcontroller also include a comparator, so I think I will use this.



The signal must be isolated, filtered, and limited on voltage so it dont damage the microcontroller:

The sircuit must give a pricise and cleen signal to the microcontroller. This is a high resolution measurement (<0.005%).

Im n newbe in electronics so I need someone to describe how to design and witch components I need.


Thanks!

Best Regards
Hans Pettersson

 

[hapetter]

Also: The signal going into the comparator (Microcontroller) must be between 0-5VDC