I have figured out the resistances from the car circuit diagram and I have turned out the first shot at that part of the circuit, I think I have the source impedance right but could someone smarter than I take a look at it and let me know if I'm ok or not... Diagram is available at http://cowshed.8m.com/car/inputs.html Thanks Anthony -- Anthony Toft -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads