Usb/dmx Interface

[Secret Weapon 0]

Hello,

 

I'm looking to get a USB/DMX interface so that I can buy a couple of DMX lights and basically mess around programming some small light shows on my computer as a bit of a hobby. My question is, what USB/DMX interfaces are out there, what should I look for, and can you get low budget ones? Obviously I'm looking to spend as little as possible really, around £50 ideally.

 

Any suggestions/advice would be greatly appreciated :)

[vokf 0]

There are some cheap ones on ebay for about £50. They look ok for budget use.

 

They will only have 1 universe (ie only 1 x 512 channels), but fine for a few lights.

 

Ideally, they should be electrically isolated which I doubt the £50 ones are, so never plug into a DMX network you've not wired.

 

For a few lights with only a few m's of cable, I wouldn't see a problem, however, if you're running poor quality cable, strapped alongside power cables and/or have long cable runs, you could see some errors.

 

For pro use with a large setup, you'll need to spend more - but for home/small mobile use, the £50 should be fine. Just remember how to switch the lights back to "auto", if the PC DMX end fails.

 

 

I have not used DMX personally, but have been reading up on it (thinking about going DMX too) - and have used RS485 (the electrical standard for DMX) in industrial control system installations.

 

 

[Secret Weapon 0]

Thanks for the reply vokf.

 

I guess you're referring to this - the JMS USB2DMX. Is the JMS USB2DMX the cheapest one out there? I see that it's compatible with FreeStyler which is good... but FreeStyler lists quite a few devices - are any of them cheaper than that?

[vokf 0]

Thanks for the reply vokf.

 

I guess you're referring to this - the JMS USB2DMX. Is the JMS USB2DMX the cheapest one out there? I see that it's compatible with FreeStyler which is good... but FreeStyler lists quite a few devices - are any of them cheaper than that?

 

I don't think you'll get anything cheaper.

Velleman do a kit (Maplins) - but its more money (but looks to be better quality, with OPTO isolation and a decent enclosure+test mode).

 

From what I've seen, many DMX modules cost around £250+, so £50 is pretty low cost.

 

I'll probably get the one you've listed at the end of the month.

 

Cheers!

Jason

[superstardeejay 0]

The velleman K8062 unit isn't opto-isolated, but is protected against overloads and overvoltage if it's plugged into anything nasty.

 

 

[Dream Catchers 0]

Also if you are looking for cheap ones, look at the Enttec Open DMX.

 

Jim

[Secret Weapon 0]

Thanks for the replies guys. My initial search for the Enttec Open DMX found one prices at $60 - great! However, the only UK supplier I've managed to find is this - charging £50. Does anyone know any other UK suppliers? Would you say the Enttec is better than the JMS one?

[vokf 0]

I doubt you'll get anything less than £50, possibly 2nd hand on ebay.. but I can't see any at the moment..

 

I'd expect the Enttec is better - it has more protection, and the JMS one will be fairly basic (something like a USB enabled microcontroller with a 485 line driver!).

Also, I think Gary mentioned - its better to have a module, than an all-in-one cable. As the prices are similar, go with the Enttec.

 

(oh, and £10 shipping )

 

Jason

 

[gadget 0]

I have the Velleman kit DMX controller, and dunno if its me, my laptop or the dmx controller, or just the way its implemented, but notice there is some sorta latency in the changing of a DMX value and the actual lights receiving/interpreting that dmx value.

 

In fact, even in DMX400 mode with LED par cans, have noticed that sometimes, the output monitor on freestyler will show the DMX values correctly, but there's latency in the actual DMX signal / fixture "following". (If you catch my drift).

 

If you have a cue/sequence and it runs slightly too fast, you can notice steps appear be missed. Not sure if this is a general DMX protocol thing, or if proper hardware DMX controllers would work better...? I think the Enttec PRO might be a better choice.. not sure really..

 

David

[vokf 0]

I have the Velleman kit DMX controller, and dunno if its me, my laptop or the dmx controller, or just the way its implemented, but notice there is some sorta latency in the changing of a DMX value and the actual lights receiving/interpreting that dmx value.

 

In fact, even in DMX400 mode with LED par cans, have noticed that sometimes, the output monitor on freestyler will show the DMX values correctly, but there's latency in the actual DMX signal / fixture "following". (If you catch my drift).

 

If you have a cue/sequence and it runs slightly too fast, you can notice steps appear be missed. Not sure if this is a general DMX protocol thing, or if proper hardware DMX controllers would work better...? I think the Enttec PRO might be a better choice.. not sure really..

 

David

 

There will be some delay between setting a value, and it being seen by the DMX fixture.

From reading online, you should be able to set the number of channels that are sent - if you've only got a 4 or 5 fixtures, each with a max of 16 channels, you only need to send 80 DMX channels - as opposed to the full 512! This should up your refresh rate.

 

However, on a standard 512 "send", you should be getting 10's of updates a second- 512 channels will take 18ms to send (although there is a break/start sequence to add to this) 80 channels will take 2ms!

 

I wouldn't have thought a different USB>DMX module will be better for speed. USB is far faster than DMX, and assuming the controller can do the trival job of sending the data out via DMX, I very much doubt the bottleneck is there.

 

The different modules appear to have better protections (opto isolation, over/under voltage etc) and also multiple universes (multiple DMX networks). I would be surprised if many mobile DJ's need more than 1 universe.

 

I suggest:

-Double check you've added a terminating resistor/connector on the DMX out of the last fixture. There will be cheap to buy or make (just a connector housing and a simple resistor)

-Set the addresses of your DMX fixtures to be consecutive (no large gaps!)

-On the PC software, see if you can reduce the channels you send to cover what is needed for your network.

-Check your cables are screened and not run parallel to power/speaker cables. Speaker/mains cables are not normally screened, and will generate noise.

On a DMX system, noise should not be a big problem - the network is fairly immune, but if any does effect the data, it should be corrected by the next update (10's of times a second, or faster).

 

I'm not sure what kind of latency you are seeing - if its really bad, I would suspect the PC/Software.

 

 

 

I hope to get my own USB>DMX module soon, I've now got 5 DMX lights :-)

 

[gadget 0]

Part of me thinks the latency is due to the way the velleman module is implemented - on the laptop it appears as a HID (Human interface device), almost like a buffered serial port... Its not the fasted type of driver out there.

 

I think the Entec pro USB unit comes with its own USB driver, so in theory should be better.. The OpenDMX version afaik isn't as good as the PRO version, as I think that uses something similar to Velleman kit to drive it (not sure though - can't remember now!)

 

I am sure I read somewhere you can set the timing signal or something on the enttec pro...

 

Is DMX fast enough to send strobe-like speeds through though? I don't think they are...

 

Will have to look at freestylerDMX to see if it is possible to reduce number of DMX channels in use - i only use up to 63 at most (and 8 x 4 is taken up with LED par cans if they're in use) otherwise there's only 4 x major fixtures + DMX dimmer pack for the PAR56 cans..

 

EDIT: Hmmn, no options on Freestyler, dammit

 

David

[superstardeejay 0]

Is DMX fast enough to send strobe-like speeds through though? I don't think they are...

 

Of course it is! You only want to strobe at..what..10 or 15 times a sec surely. DMX transmits at 250 kilobaud (250 thousand bits per second) at 8-bit resolution to a max of 512 channels sent consecutively with start & stop bits and small gaps in between to signify new channels.

 

I use the Velleman kit..there's no latency at all. If there was, it would really screw the pan and tilt vectors on scanners!!

 

My Velleman plugs and plays as 'USB K8062'. (no drivers needed). The hardware ID is embedded in the microcontroller ROM in the unit. XP installs it in Device Manager as 'USB human interface device'. Maybe the software you're using is causing the problem. Have you got it in a USB2.0 or a USB1? Both ought to be compatible really though i normally plug it into a USB2 (I have both).

 

Did you build the kit or was it ready made?

 

I also use freestyler and it works great with the Velleman, though there are a few quirks as you might expect with freeware, bugs etc, and running concurrent cues can sometimes make them slip slightly..though that's definitely the software rather than the interface. Dont forget, although DMX is an asynchronous protocol, there are limits to what a fixture can tolerate before juddering to a halt. Luckily the Velleman is crystal-controlled and only has to receive updates from the PC as a channel changes.

 

Maybe I'm stating the obvious here but dont forget the channels won't change immediately if any channel is set to 'fade'. It must be set to 'snap' actually during the programming of a sequence..and remain so throughout each scene in that sequence, as its possible to switch from Off>SNAP>FADE at will through any sequence. One of the bugs on my version of freestyler is that the Focus on a particular scanner keeps reverting to FADE when I want it to stay on SNAP even though I save it as a startup value.

 

Edited June 21, 2008 by superstardeejay

[gadget 0]

Cheers for that superstardeejay

 

I'm using the same kit.. so wonder if there's something slightly amiss somewhere that's causing it to not work at the correct speed as its supposed to do..

 

It of course, could be my laptop! Will have a go at installing on a different proper desktop PC and install freestyler there.

 

I do have a VOIP USB handset that also says it can talk USB2, bt only talks USB1, so that could be related to it..

 

I know freestyle does go weird quite a few times.. now and again it'll lose fixtures and sometimes buttons and cues.

 

In theory if I press the flash buttons (which are assigned keyboard shortcuts), I should get an instant 'on' from whatever fixture it relates to (e.g. ALL 300w PARS on, ALL LED PARS on).

 

Could I in theory create a 'strobe' cue that should do all the LED par cans to switch on/off rapidly, and they should in theory follow suit, but sometimes it doesnt quite work properly.

 

I wonder if the last item in the chain is being terminated correctly (spinmaster dipswitch setting). Think I'll go buy a 120ohm resistor and try it on the last fixture just to make sure its working correctly...

 

Cheers,

 

David

 

[Dream Catchers 0]

Do any of you have problems use the sound activation on FreeStyler?

 

Jim

[gadget 0]

Do any of you have problems use the sound activation on FreeStyler?

 

Jim

 

In what way? I personally think it could be improved. And I wish I could do Random DMX outputs *and* run the cue at the same time (you can only do one or the other).

 

 

Oh, my velleman K8062 appears to be connected as a USB 1.1 device. Can it not do USB2 ?

 

 

David

[Dream Catchers 0]

If I try to use the sound option it runs for about 5 seconds then crashes.

 

Jim

[gadget 0]

If I try to use the sound option it runs for about 5 seconds then crashes.

 

Jim

 

Is this just the separate sound analyser applicatin popup window, that stays open, even if you shut down freestyler? I guess you're using v 2.96j as well?

 

Hmmn...

 

I have an odd issue with mine as well - if freestyler is loaded up first, beatport sync fails to startup sometimes - as if there's some kinda lock happening somewhere..

 

 

Well I noticed something earlier that if the laptop is busy (e.g. firefox loading up), DMX slows right down - oh and also that the DMX light flashes a lot slower on the DMX interface.....

 

I tried earlier whilst in the office - wired up the showtec dimmer pack (rack mount - which has one badly programmed chase pattern), and checked the mimic against the DMX400 controller. at full speed on the DMX400 controller, some channels 'skipped' (i.e. going 1,2,3,4 -> 1,2,4, and also didn't seem to be smooth / consistent speed changes.

 

I'll see if I can disable all USB1 ports on the laptop (except the one the mouse goes into)...

 

David

Edited June 26, 2008 by gadget