What circuit is used in low end isolation of RS-485 for DMX-512 etc.
applications? This application (NOT DMX-512) has maybe a few to a dozen
devices on the bus maximum and cost is important.

I know how to do a powered version with opto-isolators and a DC-DC converter
to get power over the galvanic barrier, but I don't know what people
have been getting away with in practice with *no* power on the isolated
side of the remote devices. That means that optoisolators have to be
powered by the RS-485 signal. 8-( It also means that the termination
of the bus can't be very good at all (but with slow baud rates and
relatively short distances, the reflections will have died down anyhow).

I am  primarily interested in what is actually used in quantity in commercial
products by reputable companies, not what might be possible to hack up on
a bench. Anyone?

Thanks for any suggestions,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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