Hi, Thanks for your help. The current sensing idea is the way in which I was thinking of approaching the problem was to sense change in current using and A/D converter and a PIC microcontroller. I've been searching the internet for ideas, I think what I basically need to build for the current sensing side of the circuit, is a simple digital Ammeter, but this is where I'm having touble. If anyone has any info that would help me to build what is essentially a digital ammeter, I would be very grateful. I have searched the internet for digital ammeter designs, but I'm struggling to work out what value of shunt resistor I would need. Thanks again for the advice, Steve