Hi All, I have an application that requires about 12 sensor devices over a RS485 cable, evenly spaced over about 20m with a controoler at the end.
I'd like to use galvanically isolated RS485 buffers such as IL3185 on each sensor, but would also like to not have to put isolated DC-DC converters to supply the power to the cable side of the buffers.
So can I supply +5V up the cable to all the devices to power their cable side buffers? Since it is RS485 only one sensor will be transmitting at a time so as long as the input buffers don't take much current it would seem practicable (with some capacitance and possible ferrite filtering where the power comes in to each sensor).
First, is this a pratical solution? If so, assuming CAT5 cable with a pair dedicated to the 2 wire RS485 signals, a pair to +5V and a pair to ground, how long a cable would be possible, or is it best to use a higher voltage and use a cheap LDO on the receivers to generate +5V?