Doug Fleenor Design - DMX Basics

DMX 512 A: Simple Explanation

Here's what DMX512 was intended to do

The end of a DMX512 signal must be terminated so the signal cycle can begin again.

Some Limitations of the Original DMX512 Specification

- All devices on a DMX512 link are connected in a daisy chain. The output of one feeds the input of the next.
- A cable failure anywhere on the link can bring the entire system down. An AC fault in one of the dimmers
can blow every piece of equipment on the DMX512 link: console, scrollers, fogger, etc.
- Depending on product design, as few as five devices may overload the consoles ability to drive the system.

Optically Isolated Splitters solve some of the DMX512 Problems

- Optically isolated splitters were invented to overcome some of the limitations of DMX512. A cable failure on one output cannot affect the devices on another output.
- A well designed splitter will protect against an AC fault in one of the dimmers causing damage to other equipment.
- Data errors caused by a faulty device on one link will not affect the data integrity on the other outputs.
- Some splitters have "thru" connectors. These should be used only when connecting one splitter to another with a short jumper cable. If not used, they must be terminated.
- Each output of the splitter can drive many devices.
- Just as the console can drive up to 1000' of 120 Ohm data cable, so can each output of a splitter.
- Unused outputs of the splitter do not need to be terminated.

Optically Isolated Splitters Solving Some More Challenges

- It is a good idea to place each device "type" on a separate output.
- The maximum number of devices on each output depends on the design of the devices input circuit.
- Each output can drive at least 32 devices if the devices actually meet the DMX512 specification.
- Some devices which claim DMX512 compatibility do not actually meet the specification, so fewer than 32 devices
may overload the output. The only way to be certain is to check the manufacturers literature or manuals.