From: "PICdude" > So I have a current sensor with it's output going to a PIC. I'd like > the PIC to control a "short" across the current-sense resistor and > wondering what's the best way to do this. In this case, best is > most-effective (lowest short resistance), though small size and cost > is always a factor. > > The signal being current-sensed is bi-directional, up to 10mA, and the > common-mode voltage is in the 24V range. The PIC will be powered from > 5V. I'm confused about using a single FET to do this due to the > bi-directional signal, and thinking I could use an electronic switch. What is the value of your sense resistor. What shorting resistance are you= =20 happy with? An FET will indeed pass current in both directions when turned on.=20 Unfortunately it will pass current in one direction even when off! (due to= =20 the intrinsic body diode of the device). You can wire two FETs in series to= =20 block in both directions when off. Your problem may be getting it them=20 turned on. Do you have any voltage in the system at least several volts=20 greater than the high side of the sense resistor? You would need to have (o= r=20 create) such a voltage to turn on the FETs. -- Bob Ammerman RAm Systems --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .