In my current design the AVR is connected to 3.3V but there are 2 inputs coming from an RF module, which is at 5V level.
I have read this Ap.Note. (AVR182: Zero Cross Detector)
And I was wondering if I could connect these 5V signals via resistors to digital inputs (of the AVR), based on the specific Ap.Note and the AVR's internal clamping diodes ????