Homebrew USB DMX Interface with Sparkfun FT232RL | Hacker News Reader

Homebrew USB DMX Interface with Sparkfun FT232RL

openschemes.com

38 pointszdw18 comments

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.

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...

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.

I wonder what is "RS-488" mentioned in the article. I can't find anything about that.

I suspect that his is a typo and it's the well-known RS-485, because SN75176 is a RS-485 interface chip.

Maybe they were thinking of IEEE-488?

I think it's a typo. The DMX protocol is subset of Rs-485

tangent and pretty specific, but does someone know if there is something like a diy version of Enttec's dmxis? (that is, something like a midi to dmx converter)

I didn't know about DMXIS and tried to look it up, and it seems that there is a software and a hardware component (the latter not being produced anymore), see here:

https://www.dmxis.com/dmxis/

I don't know about the software, but as for a DIY hardware solution, you can just connect a USB-DMX interface (like the Enttec DMX USB Pro) and a USB-MIDI device to a laptop and "just" have to code something to translate MIDI input to DMX output. Or use an Arduino, an RS-485 module and a few other components, that's what I once did.

Ah yes I should've been more specific - the DMXIS box from Enttec is a small piece of hardware which takes MIDI input and has an output port for DMX fixtures. Accompanied by a software to create mappings from one to the other. Would be a fun project to design and code this but I was wondering if there is anything similar out there already :)

Is there something like Freestyler for Linux?

I’ve used QLC+ in the past which worked well

I suspect this homebrew interface will work with QLC+ with no software mods necessary if you set the right settings. It already supports some commercial products that use the same FTDI chip:

https://www.qlcplus.org/docs/html_en_EN/dmxusbplugin.html

I used to use DMXControl on Windows for stage play FX lighting (on-stage things such as uplighters, fireplaces, illuminated signs etc.) and would just setup a presets board with virtual push buttons.

I had a quick skim through the QLC+ site but couldn't see whether it had an equivalent feature. Any thoughts? Thanks.

I assume we aren't talking about Earl Simmons, so WTF is a DMX, and why would I want to interface with one?

DMX in this instance stands for "Digital Multiplex" and is mostly shorthand for "DMX-512" which is a RS-485 like protocol for controlling (usually theatrical) lighting systems.

Its for things like this:

https://www.youtube.com/watch?v=S5D7SYiA6w4 Daft Punk - Around The World (Official Music Video with Audio Commentary by Michel Gondry)

https://www.youtube.com/watch?v=vemkhYYb16w Daft Punk - Around The World (Official Music Video Making Of)

Good! What is a DMX?

It's protocol used to control stage lighting equipment.

Very simple. You can set the value of 512 channels from 0 to 256. Any definition of what those channels or values mean has to be handled externally.

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