DMX Refresh rate and LEDs

[vx2000]

I'm having issues with two different brands of LED lights flickering on my system.

I have the Weidamark PAR 64 and Chauvet ColorBar panel.

 

I'm using the ENTTEC DMX USB PRO interface.

 

The flickering happens with my LED lights. Both the Weidamark LED pars and the Chauvet panels flicker.

The flickering occurs when any one of the LED control channels (RGB, and dimmer) are set to less than 100% full on. When the channels are full on, there is no flicker.

 

 

To check for flicker, the following tests were set with the RGB levels set to about 25%. Only one Weidamark LED PAR is connected to the ENTTEC and terminated. Here's what I've discovered:

 

If I set an LED PAR to channel 69

and limit the amount of transmit channels to 73 (4 channel light), it flickers about once every 2 seconds. Annoying.

 

Now, with the LED PAR light still set to channel 69, and the amount of transmit channels is set to 510, it blinks rapidly about every 250ms. Very annoying (This is how it has been setup with my other fixtures)

 

Now, check this out:

 

If I set the LED PAR to receive on channel 1 and set the amount of channels to transmit to 510, there is some small level of flickering, but is is better. Hmmm, lower channel assignment the LEDs have less flicker.

 

Now, if I leave the LED PAR set to channel 1 and set the amount of channels to transmit to 5, there is NO flicker! At least none that I could see.

 

So, it appears for my LED fixtures (both the Weidamark and Chauvet) the best situation is to have very low DMX channel assignements AND to transmit only the amount of channels needed.

It also appears the less channels transmitted, the less flicker.

 

This leaves me with the following questions:

 

1. This appears to be DMX refresh rate issue with the Enttec USB Pro widget. How can I adjust this rate with the Enttec USB PRO?

 

2. Does the refresh rate need to be higher for LEDs opposed to regular lamps?

 

3. How do I overcome this issue, especially when using a lot of fixtures and channels?

 

Please help a brother out.

[Brian]

What software are you driving the Enttec with?

[vx2000]

What software are you driving the Enttec with?

 

I'm mainly using FreeStyler, but I've tried it with others such as JS_DMX, also Abuelites (sponsered by Enttec)

I've a lso tried it with the AMDJ DMX Operator. It stll flickers, just not as bad.

Apparently due to what I discovered regarding the amount of active transmit channels.

The AMDJ DMX Operator only transmits 192 channels. This explains why is see less flicker, but it's

still annoying.

 

Using the AMDJ hardware controller and still seeing this makes me believe that it is a design fault with

these LED units (both the Wiedamarks and Chauvet). Probably with the PWM duty cycle used for dimming in conjunction with the DMX frame rate.

Also assigning the LEDs to low channels with the AMDJ controller, there is less flicker. This is what the Enttec is doing.

The Enttec is worse since using FreeStyler you can not decrease the amount of transmit channels from 512.

 

I found out about decreasing the transmit channels using JS_DMX software. It has that feature.

 

I'd like to find a program I could use with the Enttec DMX USB PRO that will allow it

to change the frame rate.

 

Can you suggest another program that might work with the Enttec?

 

The Enttec appears to be working correctly. You can set up a scene and exit the software, the

Enttec's internal buffer keeps the scene alive.

 

Steve

 

 

 

 

 

 

Well,

Enttec sent me a firmware change to accomadate the LED flicker problem.

 

The good news is, the firmware change I uploaded for the Enttec DMX USB PRO works as a "band-aid" for the flicker problem with these "cheaper" LED units. He gave me a "special" firmware update to slow down the DMX by increasing the interslot time. By default the USB PRO sends DMX at the maximum speed.

 

I have not really noticed a performance hit.

 

Enntec mentioned "they get a number of similar problems on a regular basis and up to now it has always been non compliant DMX512 lights ...

Each non compliant light reacts in it's own strange way."

 

I'm real happy to see these lights dim without driving me freaking nuts flickering!

Too bad it's a band-aid approach, but I can live with that.

 

I'd like to get my hands on some of the expensive LED pars and panels to see if they have this issue.

I heard they do not.

[Zak]

I've seen a similar issue with LED PARs connected to two different hardware controllers. I can't remember what brand they were, but I'm fairly certain they weren't expensive. They were connected with cheap looking microphone cable routed past a pair of dimmers and several speakers. I'm pretty sure that was the problem, though it's entirely possible the lights were just screwy.

[Ekij]

This is a hardware limitation of the very cheap microprocessor in the LED lights.

Basically it's not capable of doing the PWM (or whatever method) dimming and reading the DMX signal at the same time.

If its DMX address is set low then it can ignore the remainder of the packet once it's past so flicker occurs less often (it's less often reading the DMX packet when it should be changing the state of the LEDs).

Similarly if you slow down the refresh rate of the DMX packets, the chip spends less time looking at a DMX packet when it should be wiggling the LEDs on or off.

 

It's rather depressing since for only a few $ more the LED units could have been designed to use a chip with true hardware PWM that wouldn't distract the processor from looking at the DMX signal at all. :P

[AndrewR]

Try running MagicQ Pc from the guys at Chamsys. It has the option to output DMX at a reduced rate which has solved problems for me with fickering dimmers. (And its very very good software too!)

[rolandpartis]

Hi there,

 

I've had a similar problem running cheap RGB colourwash LED units through PCStage using the PCStage USB dongle and software. The five units are linked together, and I get a completely random flicker running through them.

 

The only foolproof solution I've found has been to use the parallel port dongle rather than the USB. I assume this is because the frame rate is lower on the parallel port interface. Its incredibly frustrating however, because I don't own a parallel port unt, I have to keep borrowing it.

 

But I'll try the MagicQ software, thanks for the heads up.

[david.elsbury]

Lightfactory allows you to adjust the frame rate.

[live]

Lightfactory allows you to adjust the frame rate.

 

 

As does Lightjockey

Quite a common fault on the lower end led's. Also has anyone else re-alized that the showtec and stairville gear can't be addressed above 252 as they use the end dip sw as a function sw!!!

[peternewman]

Also has anyone else re-alized that the showtec and stairville gear can't be addressed above 252 as they use the end dip sw as a function sw!!!

I don't think my Eurolite ones went higher than 128 initially. But then if they aren't willing to pay for a microprocessor with enough on-board PWM, they're hardly going to pay for one with enough inputs to allow full addressing and config are they?

[live]

Also has anyone else re-alized that the showtec and stairville gear can't be addressed above 252 as they use the end dip sw as a function sw!!!

I don't think my Eurolite ones went higher than 128 initially. But then if they aren't willing to pay for a microprocessor with enough on-board PWM, they're hardly going to pay for one with enough inputs to allow full addressing and config are they?

 

I agree, it's just a shame that most budget's won't allow consumers to use Pixelpars instead of imported "par leds" cost is always an issue (even trade cost) and they are made to a budget so most professional users (or consumers within a fixed budget/constraint) are tempted by the lower pricing. With led fixtures it is a case of you get what you pay for. IMO it's a shame as the technology with led's is the way forward for colour changers/uplighters and even floodlighting. I myself have been tempted to replace my 1044's with cheaper far eastern versions, but again function vs price always will come into the equation unfortunately, like most people if a hire/conference/install has strict financial constraint on it you will always fall back on Showtec,Stairville or similar instead of Thomas or DBN.

[AV Ian]

Rolandpartis,

 

AFAIK the PCstage dongle will only work with PCstage software, a limitation I know. Thought you ought to know before you spend time wondering why it won't work with MagicQ

[DMXBandit]

You can change the frame rate in Freestyler too by opening the 'freestyler.ini' file in a text editor. The 8th item down is:

 

[MinidmxBaudrate]

value=115200,n,8,1

 

You can then edit this value (115200) but I don't have any suggestions as to what you would change it to, trial and error?

[rolandpartis]

Thanks Ian, I quickly realised this - but its good to find out about some other options.

PCStage is useful because we run AV and sound from it as well - I've found its the best program out there to do all three. I think we'll have to upgrade the lights rather than the software.

[Ekij]

It occurrs to me that some software starts brodcasting the DMX again as soon as it's finished.

However the lantern wants as long as possibel after it's seen it's own address, before the packed starts again.

We have been discussing keeping the LED units address low or slowing down the rate of brodcast of the packets but there is a third option that might help.

If you increased the amount of the lacket after the LED address it would also have a useful effect. This should be possible by getting the desk to transmit information for the last possible DMX address, this ensuring it doesn't start with the next packet after the last used DMX address.