I'm trying to desing a 4-20mA receiver for arduino and I have a couple of questions. first, this is what I base my desing on:
First, I think I understand most of the design, except for the R5 resistor... I'm not sure but is this resistor divide by 2 the input on the U1B ?
Secondly, that design work with AVR board, but I want to make it compatible with 3.3v base board. I can't have a lower than 1 gain so another solution is to put a serial resistor like R5 to divide the voltage at the input of U1B ( that's were this resistor bugging me).
another thing, if not 4-20 device is connected to the input receiver, the output , with the 1V to 0 offset, will be -1V. so to protect the board, can I put a reverse diode from ground to the receiver output or at the output of the U1B ? or a better solution...