I am waiting on the schematic but what I was told is they are using Analog Devices ADUM1400, quad channel digital isolator http://www.analog.com/en/prod/0,2877,ADuM1400,00.html So it would appear to me that this effectivly isolates.....waiting on the rest of the schematic to see what else on that side of the isolator This will be pretty hard to short circuit, at least on purpose or wiring as its all in the same box Spehro Pefhany wrote: At 07:18 PM 11/2/2005 +0100, you wrote: > > why? just to buffer it into the PIC. Although the resistor > > will be within inches of the PIC > >But why 'buffer' it into the PIC? what would be the benefit over a >straight connection (with some protection and/or filtering, but that >will be required anyway)? An op-amp buffer will have higher input impedance, allowing more reasonable component values for the protection and low-pass filtering. BTW, for protection against a shorted 2-wire transmitter, it's not unreasonable to allow for 24VDC input voltage at relatively high current. That will cook the precision input resistor out of tolerance quickly unless it has a fairly high rating (or some other form of protection). --------------------------------- Yahoo! FareChase - Search multiple travel sites in one click. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist