Northlight DMX 512 Servo Controller

[Denny]

I finally have ALMOST all the pieces to start experimenting with animatronics. I am still hoping for the LOR DIO32 board and servo daughter boards, but since the world of audio-animatronics is all new to me, I decided that I can't wait to start applying theory to reality. So, I decided to use this servo controller to experiment with movements, etc.

I have:

Servo Controller http://home.att.net/~northlightsystems/DMX512toRCservo.htm

Six servos

5 and 12 volt DC power supplies

Male and female XLR connectors

However, I forgot about the wire to make the connections between the XLR connectors and the Servo Controller. According to the instructions on page 19 of the instructions that came with the Servo Controller http://home.att.net/~northlightsystems/Servo.pdf "DMX requires wire suiable for RS-485." Rather than cut up one of my DMX cords to get a short length of wire for the connections, I should be able to use a length of cat 5e. Is this correct?

I was also surprised at the way the DMX in and through ports are connected (page 11). It looks like it is just the two ports wired in parallel. Is this standard for all DMX fixtures?

[-klb-]

Cat 5 is close enough, especially for testing, and it should be better than mic cable!

Yes, all DMX is just wired in a straight line from in to out.. The key is keeping the side branches as short as absolutely possible. Each side branch creates a time delayed reflection of the data on the bus. The longer the side branch, the greater the delay, and the stronger the reflected signal..

[Denny]

Thanks for the information and confirmation; now, I feel ready to get started!

[Steven]

Denny wrote:

I was also surprised at the way the DMX in and through ports are connected (page 11). It looks like it is just the two ports wired in parallel. Is this standard for all DMX fixtures?

Not just DMX fixtures. All LOR controllers, and any proper RS485 network, are wired that way.

[Denny]

Not being familiar with DMX, I remember one of the troubleshooting recommendations someone made for a problem was to make sure that the DMX cable was plugged into the fixture input, not the through. Just to satisfy my own curiousity, why would it make any difference since they are wired in parallel (other than one is female and the other is male)?

[Steven]

The Northlight Systems specifications sheet you linked to has a clue to the reason you may have heard that problems can be caused by plugging into the wrong port:

Devices containing three or more DMX512 ports may provide a passive link between only two of the ports.

A "passive link" is simply two ports wired in parallel. If a device has more than one through port, then at least one must be driven by a buffer/repeater. A DMX buffer/repeater is unidirectional because the DMX protocol itself is unidirectional. (As opposed to the LOR protocol, which allows controllers to be polled by the HWU to detect them or by the show player, to allow interactive inputs.)

I'm not a DMX expert, but I would expect that almost all DMX devices would have a passive link (direct parallel wiring) between the input and the through ports.

[Denny]

Thanks Steven. Although I used DMX last season, I am still learning to tread water with DMX. This is my first attempt to do something with DMX that isn't basically plug and play. Great thing about this hobby, besides blinky-blink, you can actually learn something with a lot of outside help available for the asking. Thanks again for the clarification.