Refresh Rate Problems

[kikabyte]

I have purchased one of these PCB DMX – 8 Relay Board:
http://cpc.farnell.com/HK00855/car-leis ... ents-1d493

and plan on using it to operate LED’s around our stage. Basically, you set the address, and when the value of each channel moves past 200, it switches the particular relay on…

BUT

When all of my other fixtures in Freestyler are off, and all of their channel value’s are set to ‘0’, the relay board works fine. But as soon as a few other fixtures are being used, the relays switch on and off very quickly and ‘chatter’. As soon as I set everything else in freestyler back to off, they stop chattering. I have also found that the more fixtures in use, the slower the chattering gets. In fact, when everything is in full swing, they chatter very slow.

I have messed about with both my Velleman, and my Enttec open and can’t seem to get the refresh rate down, or alter anything in Freestyler to help the situation. I have also checked my leads, and tried a terminator…

Has anyone got any ideas? Do you think using something like the entec pro would help? As all of the processing is done by its on-board processor?

All of my lights work perfectly with my setup, but for some reason, this item seems very venerable to things not being right.

Any help or comments much appreciated!

[remco_k]

First the one thing that comes up in my mind. Ofcourse you did check that and you know how this works, but I have to ask to take out all posibilities:
It looks like an DMX address overlap. Your relais board takes 8 DMX addresses, so setting its DMX address to 1, it actually uses 1 through 8.
Then, if you programmed some other DMX fixture (partly) on (or over) addresses 1 to 8, you have these problems.

Next, check FreeStyler's output form )menu Edit->Show output). See if the selected DMX channels are scattering there also. If yes, you know that FreeStyler or your own sequence is the source of your problem.
From there you might even isolate the problem to your specific sequence.

[kikabyte]

Hi Mate,

Yeah I've just been through all the addressing and everything is separated nicely. I've checked through the show output and there is nothing odd happening, I did a quick reset to make sure no patches we're in operation.

It appears to be either freestyler, or the interface.

I switch on all 8 of the relays using their set addresses (150 - 158), say set their value's to 255, then start increasing the values on for example addresses 1 - 10, as soon as their value alters from '0' they start to chatter.

I'm under the impression that freestyler stops outputting the value of the channel if the value is set to '0', so as soon as freestyler starts outputting more than say 15 channels, the speed of which the value's are transmitted slows down, and so my relay board can't handle the slow speed. So in effect, they receive the signal, switch on, but then they switch off quickly whilst they wait for another value... so the more channels freestyler has in action, the more time it takes for their value to come up again....

What do I do?? ahhh!

[remco_k]

I'm under the impression that freestyler stops outputting the value of the channel if the value is set to '0', so as soon as freestyler starts outputting more than say 15 channels, the speed of which the value's are transmitted slows down, and so my relay board can't handle the slow speed. So in effect, they receive the signal, switch on, but then they switch off quickly whilst they wait for another value... so the more channels freestyler has in action, the more time it takes for their value to come up again....

I dont think that this is the case, I'll try to explain later this post but it gets a little technical;
In short: DMX output always starts at channel 1, regardless of its value and ends at max channel 512 but can end earlier. Some fixtures don't support the method that a DMX transmission stops before channel 512 is reached and go like crazy (kinda your description). FreeStyler, however, always seems to output 512 channels (on my Velleman VM116/K8062), even when you need max 10 channels.

A nice test you could do: suppose that FreeStyler or your DMX interface is stopping channel output before it reaches 512 and your relais interface does not support that (wich would be faulty though), here a nice test you can do:
- Create a dimmer/switchpack in freestyler at channel 512. You don't need it for real. Just virtual. Leave its value to 0 or any, should not matter. Now you have forced FreeStyler / your DMX hardware to alway output 512 channels (i think). You might get lucky.

Below I try to explain how it works, I've used some * to go in deeper.

In general, the DMX512 protocol has these 'rules' (*):
- Output always starts at channel 1, regardless of its value. So channel 1 value 0...255 is always transmitted. This makes it impossible that FreeStyler stops outputting the DMX channel when its value is 0. If it does, everyone should have really big problems. Because then channel 2 gets to be channel 1.. And 3 will be 2.. and so on.
- The output may stop at any DMX channel but does not have to. Any DMX software could tell the DMX hardware generator to stop at adress 100. Then all DMX adresses from 1...100 are send, regardless of their values. (**) There is no posibility in the DMX protocol to start sending DMX address 50 and stop at 100.
- A fixture should contain its current values until it receives another. So unplugging the fixture from the DMX chain, should leave it in the state it was. It should be left on if it was on.

Did you do the same test with other software, maybe some software delivered with your USB DMX hardware?
Then you could isolate the problem more to FreeStyler or DMX interface/driver (***) being the asshole.

*

DMX512 data is sent using EIA-485 voltage levels and cabling practices. The DMX specification refers the reader to EIA-485 for information about the electrical signal. Data is transmitted serially at 250 kbit/s and grouped into packets of up to 513 bytes, called 'slots' in DMX512-A. The protocol uses 1 start bit and 2 stop bits with a little endian data format. The start of a packet is signified by a break of at least 88uS followed by a "Mark After Break" (MAB) of at least 8uS, extended in 1990 from the 4uS specified in the original 1986 standard. The break is a signal to receivers to start reception. After the break up to 513 slots are sent. The first slot is interpreted as a "Start code" that tells receivers what kind of data will follow. For lighting fixtures and dimmers a start code of zero is used. Other start codes are used for Text packets or the System Information Packet (SIP), proprietary systems, or for the RDM extension to DMX.

The remaining slots make up the actual level data. Up to 512 slots can be sent, and it is the job of the receiver to count the slots to keep track of the channels. As there is no error detection or correction in DMX, it is vitally important for receivers not to miss slots, and to discard packets if framing or buffer overflow errors are detected.

A full packet takes approximately 23 mS to send, corresponding to a refresh rate of about 44 Hz. For higher refresh rates, fewer channels can be sent. This is accomplished by simply starting a new packet before all 512 channels have been sent. The minimum packet length is equivalent to 24 channels. Most transmitters send all 512 channels because many receivers have trouble with shorter packets.

Source: http://en.wikipedia.org/wiki/DMX512-A

** Recently I started a topic about that FreeStyler always seems to output 512 DMX channels. Even when we only need (say) 10 channels. The DMX protocol has this implementation (always starts at 1 but can end on channel 10). FS always outputs 512 channels?
So, for your information this is a good thing, because it looks like FreeStyler always outputs 512 DMX channels.

*** Try the latest driver version of your DMX interface

... just my 2 cents.

[kikabyte]

OK! Well it did get a little technical, but I’m hanging in there!

I’ve dug out the velleman test software thing, and had a play!

My little DMX PCB board is set at channel 1. So I increased the values of the channels one by one, listening to the relays click over when their value gets high enough. Then I continued to increase the value’s of channels past my fixture address. I got to 19, and suddenly the relays start to chatter. If the value of channel 19 was set to ‘0’ it remained silent, but as soon as I altered it to anything but 0, it chatters. Interestingly enough, I was installing the new version of freestyler 3 whilst I carried out my test… and… when leaving channel 19 at ‘0’, every now and then the relays would chatter slightly at random times… the more intense the installation procedure, the more they chattered… when the computer had nothing to do, they stayed quiet… so when I opened up my video editing software, and cubase at the same time, they went mad.. again, not altering any of the dmx settings or values from when my laptop was idle.

Does this make anything clearer? It certainly removes freestyler from the equation!

Thank you so much for all of your input up till now, I really appreciate it!