DMX – a few findings

Installed QLC+ on my laptop. Great tool, giving up on bying a DMX controller.

QLC+ recognizes my FTDI cable adapter (and my Waveshare adapter):

Plugin   Device                            Input   Output  Feedback
 DMX USB  1:USB-RS485 Cable (S/N:FT4NMHF6)  -       X       -
 DMX USB
 This plugin provides DMX output support for DMXKing ultraDMX range, Enttec DMX USB Pro, Enttec Open DMX USB, FTDI USB COM485 Plus1, Vince USB-DMX512 and compatible devices.

No input support available.
1: USB-RS485 Cable (S/N: FT4NMHF6)
Device is operating correctly.
Driver in use: libFTDI
Protocol: Open DMX USB
Manufacturer: FTDI
DMX Channels: 512
DMX Frame Frequency: 30Hz
System Timer Accuracy: Patch this widget to a universe to find out

In the plugin settings I can change Mode. Open TX (above) allows sending DMX messages, Open RX allows receiving. And it works.

Using the two USB adapters – one on my laptop and the other on EV3 – I used QLC+ to test my scripts on EV3:

  • using QLC+ as controller, my EV3 python scripts (pyftdi-based) can decode messages on any of the 512 channels… as long as I lower DMX frame frequency to 9 Hz.
  • using the Ev3 as controller (python scripts using dmx485) I can receive messages on all 512 channels on QLC+

but…

  • using laptop as a controller (python dxm485 instead of QLC+) the same pyftdi-based scripts on EV3 no longer work… unless I force sender object to stop immediately after the first frame:
sender.start()
 while True:
    sender.start()
    sender.set_data(bytes(CMD))
    sleep(0.115)
    sender.stop()
    sleep(1.0)

It seems dmx485 forces a DMX Frame Frequency too high for my decoding scripts to keep up – it seems to be a limitation of EV3 because reverting the scenario (EV3 as a controller with dmx485-based script and laptop as a receiver with pyftdi-based script) it works.

Good that QLC+ has an option to adjust it – 9 Hz isn’t good for light animations but is more than enough for what I want. Will use it as a DMX controller from now on.

Interesting, QLC+ also has a MIDI plugin. It can listen to MIDI channels and take actions… like activating a DMX fixture when a selected note is played.

So… MIDI brings me to DMX… DMX brings me back to MIDI. Such a small world.

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