On my 328P based setup, I seem to recall that after coming out of sleep, I had to take an ADC reading and discard it, then take the next reading as required.
Try doing 2 reads of A0 when you come out of sleep.
On my 328P based setup, I seem to recall that after coming out of sleep, I had to take an ADC reading and discard it, then take the next reading as required.
Try doing 2 reads of A0 when you come out of sleep.