Different kinds of DMX?

[stevep]

Bit confused on this one

 

I have two different moving lights - a showtec Phantom75 and an equinox fusion100, both work completely fine with a direct DMX cable from my avo titan however using the avo is complete overkill for the task, so I wanted to use a 12channel manual desk (https://www.thomann.de/gb/stairville_ddc12_dmx_controller.htm)- problem is that the Showtec unit works fine but the equinox unit is completely unresponsive despite saying it's receiving DMX.

I'm using the same DMX cable on each (i.e. I switched the cable from one unit to the other) and the line is terminated.

 

Any thoughts?

[jonhole]

There are two possibilities that come to mind:

 

1) There is a range of DMX speeds allowed - lighting consoles can be anywhere within that range, but fixtures have to support the whole range. However, if the fixture doesn't support the whole range (which is unfortunately common) you'll find some consoles appear to "work" and others "don't work". Although it looks like an issue with the console, it's actually an issue with the fixture.

 

2) Simpler consoles don't always output all 512 channels of DMX (especially something like that console which only has 12 channels of DMX, and isn't patchable). This is completely allowed, but some fixtures get confused by it and stop responding.

[timsabre]

As Jon says the Thomann controller only outputs 12 channels and I would think that is the problem.

 

The equinox unit has a 5 and a 15 channel control mode - what mode do you have it set to?

 

Even if you have it set to 5 channel mode, it might be looking for all 15 channels...

[stevep]

Cheers guys-I tried the equinox unit on both 5 and 15 channels and same lack of result.

[timsabre]

Cheers guys-I tried the equinox unit on both 5 and 15 channels and same lack of result.

 

Mmm. I assume you have it set to Address 001. I suspect that even in 5 channel mode the software is continuing to look for 15 channels, but that controller is only sending 12 so it is never getting a full set of channel data.

[Kazeja]

 

Simpler consoles don't always output all 512 channels of DMX.

 

 

I have been caught out by this before and it is so true.

 

I had a showtec 48 channel console connected to Betapacks and movers. The movers (DMX 13-48) were fine but the BPs (DMX 1-12) were erratic in response. Found out Showtec was only transmitting 49 DMX channels. Putting the showtec DMX 49 signal through a re-generator (all 512 channels transmitting) for testing purposes showed there was nothing wrong with the BPs. I tested a Trancension/Showtec 6 channel desk and found it only transmited 7 DMX channels and I suspect that your 12 way desk is probably only transmitting 13 channels which may confuse some devices that are expecting a lot more.

 

Hope this waffle makes sense.

 

K

[Don Allen]

Some manufacturers may only generate the nominal number of DMX channels their desk has, e.g. 24 DMX channels for a 12/24 desk, but fit their 24 channels into the normal DMX 512 tansmission timing. These desks will work with most DMX lighting.

 

Some manufacturers may only generate the nominal number of DMX channels their desk has, e.g. 24 DMX channels for a 12/24 desk, but transmit or send their 24 channels at a faster refresh rate.This means that the overall DMX data stream is not the same as normal DMX 512 data streams, so a lot of DMX lighting will not work with these desks.

 

In general. using generic desks such as a 24/48, I can put a LED Par that is in a 9 channel mode on it, with a start address of 20 and the led par will work ok, as I have control of the dimmer and colour channels and the strobe, speed etc are not available, but also not required. Where this does not work is where the desk manufacturer uses a faster refresh mode, or the led par manufacturer has marginal timing, that just misses out on the desk manufacturers marginal timing.

[timsabre]

Hi Don, it is not normally the refresh rate that causes trouble but the amount of idle time in the DMX, either spacing between the individual channel values (called interbyte spacing, and not specified in the DMX standard), or gap between one packet and the start of the next. On cheaper fixtures with simpler microcontrollers, they rely on this space to run the fixture. Some controllers (usb dongles particularly) just bang out the DMX as fast as possible, and the fixture just can't keep up.

 

(I've spent a long time designing cheap fixtures and trying to overcome this problem... )

[Jivemaster]

Better DMX sources are usually more compliant than cheaper ones. Some cheaper DMX receivers are more or less tolerant of out of spec DMX.

[martinw]

Strictly speaking, almost all DMX compatibility problems are due to firmware issues in the receiver, rather than the transmitter. Because the spec is so loose and open to interpretation, it's actually quite hard to make a transmitter which isn't 'compliant', but this makes the receiver more tricky to design because you have to cope with every eventuality, and test against a lot of sources. Sources which send a small number of channels, or which (as Tim says) don't have any inter-byte time do tend to cause problems, and whilst they are totally compliant with the spec, they are perhaps being rather unhelpful.

 

Having said that, it used to be the case that some cheaper microcontrollers would struggle to keep up with DMX where there was no inter-byte time, but this has long since ceased to be a valid excuse. Very fast microcontrollers are now so cheap that this problem is always due to poor receiver firmware design.

 

Martin

[timsabre]

Fast micros may be available but if you look inside cheap lighting fixtures you will still find the old favourites.

Anyway when it comes to hardware related stuff like stepper motors and pwm of lots of leds, the "fast" 32 bit micros don't look quite so clever. In fact pic8 and AVR8 beat most of the Arm cortex stuff hands down for pin twiddling.