We are feeding the op-amp from a LM2574-12 switching regulator and the pic is fed from a LM2574-5.0 switching regulator. The power supply is a half-wave rectifier because we need to use a common ground. We also have a bi-directional zener on the input along with a MOV to help surpress any spikes. I'm not sure what else we could do to isolated this little puppy.