Hi Mak,

Noise, noise, noise. Make sure your power supply is not causing noise in your circuit. I recently ran into this problem doing a serial acquisition experiment. I was getting noise through the serial port somehow till I hooked up my circuit to a 12V rechargeable battery. I made my power supply so that could be the cause of course so watch out for noise in an AC powered power supply. TRY A BATTERY SUPPLY WHEN ALL ELSE FAILS! If that solves the problem, troubleshoot your power supply.

TTYL,

Dave Kaleta