Homebrew USB DMX Interface with Sparkfun FT232RL

Re:Homebrew USB DMX Interface with Sparkfun FT232RL by rapjr9 on Tuesday August 02, 2022 @03:11PM (#32323004)

Note that the FT232RL is NOT optically isolated on the data lines and power from USB is also not transformer isolated. So if one of your light fixtures happens to short out and send 120VAC down the data or ground lines your computer and maybe YOU are toast. Anything else connected to the same system (mixing board, DMX-512 console, video gear) could also be fried. Here's an example of how to do it right:

https://www.analog.com/en/analog-dialogue/articles/isolated-...

A homebrew interface like this may be ok for learning, but if you plan to get income from running a light show use an isolated interface or you will be liable if anyone gets hurt.

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Re:Homebrew USB DMX Interface with Sparkfun FT232RL by stonegray on Wednesday August 03, 2022 @10:50AM (#32332535)

This existing design perfectly fine for a DMX transmitter. Unlike receivers, DMX-512 transmitters are not isolated. The isolation required in receivers will protect the transmitter from the condition you described.

EIA-485 specifies the electrical properties of the signal, however the ESTA E1.11 (DMX-512) specification further constrains it in section 5 and 6 in regards to grounding and isolation.

Annex A of the specification does provide allowance for non-isolated transmitters where common-mode voltage is expected, but this is specifically not recommended:

https://tsp.esta.org/tsp/documents/docs/ANSI-ESTA_E1-11_2008...

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Re:Homebrew USB DMX Interface with Sparkfun FT232RL by loansindi on Thursday August 04, 2022 @01:35PM (#32345861)

You'd be surprised what kind of terrible things can happen on a run of DMX cable. I've seen enough transceivers exploded out of their sockets to be wary. The leading US manufacturer of lighting controls continues to use socketed DIP rs-485 transceivers exactly because they tend to take hits and fail.

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