DMX512 EXPLAINED

DMX512 stands for digital multiplex 512.  This means that 512 channels are controlled digitally through 1 data cable.

A channel is 1 set of 255 steps that are assigned to control attributes in each light.  This may be a colour like red, green or blue, and intensity, strobe, pan/tilt or other attributes.

This is pretty incredible if you remember some old analogue control systems where you had 1 pair of wires for each channel of the console!

Data is sent down this line via pulses of electricity from a lighting console, into your fixtures that are usually “daisy chained” together. This means that you plug the initial DMX cable into the first fixture, the “OUT” of the first fixture into the second fixture, etc, up to 32 fixtures maximum (more on that below).

DMX is not manufacturer specific.  DMX-controlled lights from any manufacturer can be controlled by any DMX console – even if that console is made by someone else.

One of the first things you’ll have to do when you begin lighting is to address your fixture or dimmer

An address is the location in the 512-channel universe that the DMX device begins.  Often, this is referred to as the “start address” since it is the first address that a given fixture uses.

If you have a one-channel device, like a conventional channel on a dimmer, then you can address the fixtures one after another.  This would give you the first on address 1, the second on 2, etc.

However, if it is a multiple channel fixture, like an LED or moving light, you need to be sure and leave the total amount of channels the fixture takes open before patching the next fixture.

So, if you have a 3-channel fixture starting at channel 28, the next open address would be address 31.

If you don’t do this, you’ll be trying to control one light, and another one may start doing something you did not expect!

The good news is Most moving light and PC-based consoles will work out the channel patching for you, but some basic conventional consoles do not!

What are the limitations of DMX 512?

DMX is a great protocol to run our lights, but it can’t do everything.

One rule is that you can’t have more than 32 devices on 1 DMX cable run.

However, this isn’t a hard and fast rule, as different DMX devices have different electrical resistances, so that number may be slightly higher or lower.  Be sure to play it safe, as you don’t want to have a data issue and lose control of some or all of your lights.

I typically won’t go over 16 fixtures myself, to be on the safe side.  Remember: When lights are hung in a position that you require a ladder or lift to troubleshoot a data issue, play it safe and keep your numbers down!

While you can technically run DMX signal for 1800 feet, I’ve found that anything over 500 feet gets a little scary and can get flaky depending on the number of fixtures attached.

The good news is that if you do begin to have signal problems, you can always split and boost your signal to solve them!

DMX512 employs EIA-485 differential signaling at its physical layer, in conjunction with a variable-size, packet-based communication protocol. It is unidirectional.

DMX512 does not include automatic error checking and correction, and so is not an appropriate control for hazardous applications,[1] such as pyrotechnics or movement of theatrical rigging. False triggering may be caused by electromagnetic interferencestatic electricity discharges, improper cable termination, excessively long cables, or poor quality cables.

Source: Wikipedia