I have never seen an 485 optoisolated at the output line...
Just because you'll have a lot of problems with line impedance.
Use optocouplers isolation ( you need three ) and a separate power supply
for line driver/receiver.
However, if it works with 1:1 transformers and at least 30 devices on one
1200m EIA485 line, please let me know ! It should be interesting !

If you mean by basic flyback, an isolated power supply, then computing the
transformer means only using the Faradys law at a known F and B

regards,
Vasile
http://www.geocities.com/vsurducan


On Wed, 4 Dec 2002, TNT wrote:

> Hi All,
>
> I want to build a BASIC FLYBACK to isolate the serial communication on a PCB
> (485).  I want to supply the isolated section by a transformer.  Do you any
> idea for the transformer...
>
> I was using a MAX243 with a coilcraft transformer, but it is too
> expensive...
>
> Thanks a lot,
>
>
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