Thứ Ba, 27 tháng 9, 2011

How to build DMX512 terminators

How to build DMX512 terminators

(I say terminators 'cos you will end up building lots of them)
DMX512 terminators are easy to build; you need no more than a 5 pin XLR plug, a 120 ohm resistor, and a little time. Holding on to them once you've built them is the hard part. Get down to the local DIY store and buy a engraving tool, and engrave the fact that this plug is a terminator, and that it belongs to you clearly on it. You'll still "lose" them, but at least after a few years you'll be seeing your terminators around the place, and be able to grab them back!
The only outstanding question is what power the 120R resistor should be? In the photo below, the resistor shown is a quarter watt jobbie, chosen primarily because it looked nice for the photo. Human nature being what it is, the previous set of instructions said use a quarter watt resistor, cos that is what I was looking at whilst writing up the page.
This prompted an item of mail from Doug Fleenor of Doug Fleenor Designs to write to me and to suggest that I was being a bit mean specifying quarter watt, since a good 5V signal into 120R gives about 0.2W dissapation, which is not exactly erring on the margin of safety.
The silly thing is is that my 'normal' resistor in a DMX512 terminator is not a quarter watt device, but a 0.6W device, (from Maplin part number A120R), but I didn't photo one of these becasue they are a boring all blue thing!
My current recommendation is a 1W 120R power metal oxide resistor, (from RS Components part number 214-1018), this device easily fits in an XLR body, and has a reasonable safety margin.


Solder a 120 ohm one watt resistor between pins 2 and 3 of the XLR5.
Thats it.

Inside the plug