Wouter van Ooijen wrote: > > > But I want to avoid needing a power source at the 4-20mA side. > > > > So what's supplying the current to the sensor, then? > > Some source that I would like to avoid connecting to (two wire interface > instead of three wire). But if you tap into the loop at all, you're connected to that source whether you like it or not. I don't understand what the issue is. > Unless I find an easy and cheap way to couple without using power ... About the only approach I can think of that uses *zero* power on the current-loop side is some sort of Hall-effect sensor. See http://www.chipcenter.com/circuitcellar/september00/ancil/c0900eqa2.htm;?PRINT=true for an approach that avoids linearity and scaling problems. -- Dave Tweed -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu