Hi Jim,
Opto-isolating sensors in the real world is usually not overkill. But=20
you only mention isolating the signals and not the sensor power.
Just a few questions:
- part number of the encoder
- is it getting its power from the PIC board or elsewhere?
- maximum rotation speed of the encoder in your application?
You mention running RS485, which doubles the number of wires needed. =20
Have you thought about powering the encoder with an isolated DC-DC=20
module along with isolators at both ends?  I'd use a supply that's 5 to=20
10 volts higher than you need and regulate it locally at the sensor. =20
You shouldn't need to go differentially in that case.
Bill

On 3/29/2016 10:35 PM, Jim Ruxton wrote:
> Hi , I want to read data using a PIC from an absolute encoder that is
> 100 feet or so away outside. The encoder takes a clock signal and chip
> select signal and outputs a serial stream giving the position. Currently
> I am planning on  opto isolating the 2 pic inputs and pic output and
> using MAX485 RS485 tx/rx chips to send the 2 signals and receive the
> serial stream back on the isolated side. I'm curious if people think
> this is overkill. It is a one of project so the cost difference of
> adding the optoisolators and MAX485 IC's isn't really relevant. Looking
> forward to hearing some opinions on this.
> Thanks,
> Jim
>

--=20
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