DMX Termination For Dummies

[PadawanGeek]

Hi Guys. I am really not getting this whole DMX termination deal. I have looked through a bunch of threads and it is not getting through my brain...

Can you please give me a plain and simple (explain it to me like I'm a caveman), what does DMX termination do, and how do I do it?

When people say "put a 120 ohm, 1/4 watt resistor across pins 2 & 3," what does that mean?

Thanks!

[cutlunch]

Hi. The 120 ohm resistor needs to be soldered into place. One end of the resistor is soldered onto pin 2. The other end is soldered onto pin 3. Being a resistor it doesn't matter which end goes to which pin. The numbering of the pins is normaly marked on the plug. Lokk at the output plug of what you want to terminate. Probably labeled "DMX Ou"t to see which type of plug you need a female or male. JUst make sure that the metal leads of the resistor can't short against each other, pin 1 , or the metal case of the plug. Use heatshrink tubing or insulation tape to ensure this.

With termination the main thing to rember is that the terminator is the last thing in the DMX line. Eg if you have four dimmer packs and the DMX goes in the first then out to the second etc until the fourth. There won't be a lead coming out of the DMX Out on the fourth pack. This is where the terminator goes.

Just remeber some equipment comes with a builtin terminator. These normaly have a switch to put in / take out the terminator. Check your equipment manual to tell whether there is an inbuilt terminator.

Just remember that at the end of any DMX line there should be a terminator.

Hope this helps.

[CURLS]

Ok not to be a dick since i just got done flyin a bunch of PA but look at this it should awnser ur questions quite thoroughly if you take the time to research. http://images.google.com/images?um=1...dmx+terminator

[JD]

Ever hear someone shout in a gym? Hard to hear them because there is so much reverberation. If the same gym was carpeted and curtains were hung, the reverberation would be suppressed and you would be able to hear better. The rugs and curtains would absorb the sound.

In a way, that's what the dmx terminator resistor does. Without it, the signal "echoes" about the wiring making it hard for the dmx devices to hear it well. (ok, bit of a stretch) The terminator kind of absorbs the signal at the end of the loop suppressing all that electronic echoing. Note I say "kind of" and "bit of a stretch." The actual nature of what is going on is a bit more complex, but I think the "gym" analogy works pretty well. Hope this helps.

[PadawanGeek]

Thanks Guys.

I got a 100 ohm 1 watt resistor with 5% tolerance. Is this fine?

[Jezza]

In theory, it will help, but I wouldn't recommend it. 120 ohms is what is prescribed as being the correct resistance to use to terminate a DMX line. The resistors are maybe a few cents at any computer/electrical supply place. It shouldn't be an issue tracking one down.

[Van]

Originally Posted by PadawanGeek

Thanks Guys.

I got a 100 ohm 1 watt resistor with 5% tolerance. Is this fine?

Go to Radio Shack, they still carry resistors, < in most stores anyway. a 100ohm resistor is not going to hurt or adversly effect the performance of you system, but is best to get the right equipment.
To further the analogy if you are getting carpeting and drapes for that gym your'e shouting in and you need 120 square feet <120ohm resistor>but you've only got 100 square feet of soft goods , <100 ohm resistor> you can use what you got but it's not as effective. < god this is a crude analogy, but helpful> Now if you double the size of the gym < add more nodes/runs onto the DMX line> and you use 100 square feet of carpet again your now going to have twice as much reflection of noise. That make sense?

[PadawanGeek]

Originally Posted by Van

Go to Radio Shack, they still carry resistors, < in most stores anyway.

I went to radioshack and they only had the 90s, 100s, or 150s. I have already finished making it. Would a 150 ohm resistor work?

[Van]

Hmm it's like splitting hairs. Too much resistance and then the good signals get absorbed. If you could find them you could put two 60's in series, or a 100 and a 20 etc. it just math. Do not, however put them in parallel this will only increase the wattage handling capability. Try parts express online, or some other electronics suppliers. Frys electronics, or ... do you have a local radio supply store, or computer network supplier? The 120 is used a lot in those apps as well.

[stantonsound]

I am not one for buying things that are easy to make. For instance, I would never consider buying pre-made stage pin cables, or twofers (socapex is a different story, that is a pain in the butt to make), but dmx terminators are only about $4-$5. I stock these with my rental gear, as they are more likely to get returned in they look like something important, rather than looking like a broken dmx or xlr connector. If it is going to take you hours of searching and driving (with gas at $3+ a gallon), just go online and order one.