LOR/Renard DMX configuration

L

Larry Hazeltine

New member
I plugged everything in last night and got a bunch of random flashing before even loading Vixen. Something is wrong!

My setup:
PC - USB DMX dongle - special cat5 wired to Renard - 2 Renard 24 controllers - special cat5 wired from Renard to LOR - 4 LOR controllers

The Renards work fine when plugged into the dongle - I can run a sequence on Vixen and control the lights. The problem comes when I plug in the LORs.

I don't have a 120 ohm terminator anywhere in the line and I think that is the problem. The question is where should I put it? LOR "senses" the type of network it is on (according to their website), so it doesn't just run straight DMX. I am thinking that a terminator at the end of the LOR chain won't do anything because of the way LOR handles the data in and out.

Would it work to put the terminator at the end of the Renard chain and still allow it to pass the signal to the LOR? It wouldn't be very hard to add a resistor to the special cable I made to connect the Renard to LOR.

If the terminator does what it sounds like it does, would this mean I have to change the order of my system to have LOR first? I'd really like to avoid that if possible.
 
Re: Terminator

Larry Hazeltine said:
...

The Renards work fine when plugged into the dongle - I can run a sequence on Vixen and control the lights. The problem comes when I plug in the LORs.

I don't have a 120 ohm terminator anywhere in the line and I think that is the problem. The question is where should I put it? LOR "senses" the type of network it is on (according to their website), so it doesn't just run straight DMX. I am thinking that a terminator at the end of the LOR chain won't do anything because of the way LOR handles the data in and out.

Would it work to put the terminator at the end of the Renard chain and still allow it to pass the signal to the LOR? It wouldn't be very hard to add a resistor to the special cable I made to connect the Renard to LOR.

If the terminator does what it sounds like it does, would this mean I have to change the order of my system to have LOR first? I'd really like to avoid that if possible.
Click to expand...

The normal use of a terminating resistor is to maintain the characteristic impedance of the line. RS485 (which is the transport for DMX) will feed multiple devices (up to 32) in parallel along the length of the cable, but expects a termination of 120 ohms at the end of the line, rather than an open circuit. This will minimize reflections back down the line, which may confuse the receiving devices.

However, the Renard controllers each generate a "new" data stream onboard, so there is minimal reflection, even if not terminated. I am not familiar enough with LOR to know if they regenerate the DMX stream or simply pass it along via the "DMX Out" jack.

Make sure your LOR boxes are addressed AFTER the Renards if that is where they are in the chain. As I understand it, the Renards will be stripping off 8 bytes for each PIC the datastream passes through, so if your LOR boxes are addressed too low, the corresponding bytes for those channels will be stripped off before the datastream reaches the LOR boxes. They will never see matching bytes, so will remain dead.

I am not a lawyer (strike that, i mean DMX/LOR user), so this is just my understanding of the protocol as implemented in Renard. Take it with a 5-pound bag of salt. :rolleyes: :rolleyes: :rolleyes:


Good Luck! :)
 
Re: Terminator

I disconnected the LOR controllers and the Renards worked fine. I put both cable adapters together* and plugged into LOR and they worked fine. I put it all back together (Ren adapter cable to the Renards then the LOR adapter cable to the LORs) and only the Renards worked normally. The LORs were still blinking randomly.

I also tried swapping +/- on the cable I made to adapt from Renard to LOR with no luck.

Finally, I put the LORs first with both adapters then made a new adapter to connect the Renards. I flashed the first Renard chip to be channel 65 and adjusted the Vixen channel outputs to have LOR on channels 1-64 and Renard starting on 65 instead of 1. Everything worked perfectly! No terminator needed for this arrangement.

* Putting both adapters together makes the dongle pinout match LOR since they run dongle>Ren>LOR
 
Re: Terminator

Larry Hazeltine said:
I disconnected the LOR controllers and the Renards worked fine. I put both cable adapters together* and plugged into LOR and they worked fine. I put it all back together (Ren adapter cable to the Renards then the LOR adapter cable to the LORs) and only the Renards worked normally. The LORs were still blinking randomly.

I also tried swapping +/- on the cable I made to adapt from Renard to LOR with no luck.

Finally, I put the LORs first with both adapters then made a new adapter to connect the Renards. I flashed the first Renard chip to be channel 65 and adjusted the Vixen channel outputs to have LOR on channels 1-64 and Renard starting on 65 instead of 1. Everything worked perfectly! No terminator needed for this arrangement.

* Putting both adapters together makes the dongle pinout match LOR since they run dongle>Ren>LOR
Click to expand...

You may want to to post this info in the LOR area, and post in the renard area if you thing this is something that could be sorted out in code/hardware.
 
Re: Terminator

Hmm - OK - what if you put the LORs first in the chain but addressed to 65 then the RENs starting at 1 as normal? I don't think there's a requirement for devices to be in physical order to their address. Chained Renards can be looked at as one big device instead of multiple DMX devices since they internally set up their own addressing.

This will be interesting since I won't have my FreeStyle until next week :???: so I can't experiment until the last minute and I'm hoping I don't have to remap all my channels in my sequences (my LORs are currently last in my addressing). I have Renards too but they don't (can't) run DMX (yet).

Good info there Larry!
 
Re: Terminator

Many Renards (for example the 24, 64, and SS series) have the 120 Ohm terminator already installed. Other designs may omit it. At 57,600 bps, the point-to-point Renard boards often work without it. Any echos have plenty of time to die out before the next bit transition. But DMX uses 250,000 bps and generally connects to multiple units, leading to longer effective cable lengths. This means any reflected echos are more likely to interfere with the DMX signal. That is why a terminator at the ultimate end of the DMX cable is mandated by the standard.

The DMX timing on the converted Renard boards is also a few percent off from the regulation bit rate. Depending on how the LOR units detect the DMX signal, they may read the data at the wrong time, misinterpret it as LOR protocol (instead of DMX) or be more easily confused by signal reflections.

It's often easier to put the LOR and other DMX equipment ahead of the Renard-DMX gear, as you discovered. This post goes into more detail why.

(yet another Don)
 
Re: Terminator

budude said:
Hmm - OK - what if you put the LORs first in the chain but addressed to 65 then the RENs starting at 1 as normal? I don't think there's a requirement for devices to be in physical order to their address. Chained Renards can be looked at as one big device instead of multiple DMX devices since they internally set up their own addressing.
Click to expand...
I hadn't even thought about that. Since LOR rebroadcasts the entire incoming signal to the output (or at least passes it on intact) I could have left my channel numbers alone and moved the LORs to be physically before the Renards. The Renards would have looked for DMX channel 1 while the LORs would start at the first channel assigned to them.

I think long-term the solution I came up with will work fine. I plan on adding more Renard controllers next year. If I leave the LORs as controllers 1-4, i don't have to reprogram the addresses each time I add another Renard to the end of the line.
 
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