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RDM Physical Layer/Hardware Discussion Discussion and questions relating to the physical or hardware layer of RDM.

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Old February 15th, 2017   #1
berntd
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Join Date: Jan 2008
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Default Hardware: Grounding of host. Opinions?

Hello

I have been grappling with this for a while.

If I build a DMX transmitter / RDM host, what should I do with the RS485 Common?

My standard way is to be a non isolated transmitter as per the DMX spec.

But, Now I am looking at USB powered transmitters that can also run of external plugpack power supplies.

The USB shields do end up being grounded or earthed via the host PC but plugpacks do not usually have mains earth continuity.

Now I am scratching my head.
What does everyone else do in this case?
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Old February 16th, 2017   #2
ericthegeek
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Default

Quote:
Originally Posted by berntd View Post
Hello
If I build a DMX transmitter / RDM host, what should I do with the RS485 Common?

My standard way is to be a non isolated transmitter as per the DMX spec.
I generally like to isolate everything (controllers and responders). The preferred topology in E1.11 is to have ground referenced controllers and isolated responders, but since you don't know what kind of devices will be connected I find it's best to isolate everything. Then you don't have to worry about ground loops forming through the DMX line.
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