> Do ya mean the serial port on a PS/2 computer? Sorry, no. I meant the mouse / keybaord little round plug sorta port. Paul S. says 25mV, I need 40mV, so I was gonna try using a 125Ohm resistor and seeing what I get - but I'm afraid I'll get a fried port :). You're probably right, though, I'd expect it to be current limited... - Chris