Hi Bill,
Thanks a lot for the reply. The encoder I'm looking at using is the=20
Bourns  EMS22A50-B28-LS6 ,=20
http://www.bourns.com/docs/Product-Datasheets/EMS22A.pdf
I was going to put an isolated 5V in 5 V out  DC/DC converter on the=20
board with the PIC using this to power the RS485 transmitters/receivers=20
and  encoder. I would prefer not to go differential  via RS485 if=20
possible because as you say it doubles my wire count. The encoder speed=20
is very slow. It is for a wind vane so just measuring position of the=20
wind. Assuming non hurricane winds :) .  So if I understand you=20
correctly you are suggesting optoisolators at the PIC and at the=20
encoder. Does this imply 3 power supplies... ie.
1 PIC power,
2 output of PIC optoisolator/ input of encoder isolator
3  encoder power

In an ideal world I would like to avoid putting any electronics outside=20
beside the encoder but I guess that can't happen?

Thanks a lot for the help.
Jim

On 2016-04-01 09:19 AM, William Bross wrote:
> Hi Jim,
> Opto-isolating sensors in the real world is usually not overkill. But
> 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.
> Have you thought about powering the encoder with an isolated DC-DC
> module along with isolators at both ends?  I'd use a supply that's 5 to
> 10 volts higher than you need and regulate it locally at the sensor.
> 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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