can't solve this voltage measurement problem

[Charles Linquis]

It also wouldn't hurt to take an average. Since 60 Hz has a period of 16.66 milliseconds, and an A/D conversion takes about 30uSecs, you could average 16 samples (a full cycle) something like this:

   ADCAvg = 0            ; Clear the variable
For X = 1 to 16
   ADCIN,x, ADCresult
   ADCAvg = ADCAvg + ADCresult
   Pauseus 1000  
   Next X
ADCAvg = ADCAvg >> 4    ; divide by 16

This should do a pretty good job of smoothing the result.

[Christopher4187]

I've tried all kinds of software routines but nothing seemed to help. I think the AC ripple is not a normal sine wave, maybe that's why.

[Melanie]

Put a 1uF Electrolytic... or even a 10uF... across the 0.1 Capacitor.

It's a Battery Charging circuit - you don't need instantaneous results. If your filters time period is a few hundred mS then goodbye to any 500Hz noise! Make sure you haven't got any noise on your 5v line - that could be throwing +VRef as well.