DMX512 (Digital Multiplex) is a standard for digital communication networks that are commonly used to control stage lighting and effects. It was originally intended as a standardized method for controlling light dimmers up to 512 dimming channels. The first standard version was created in 1986, with subsequent revisions in 1990 leading to USITT DMX512/1990, ANSI standard in 2004 and revision in 2008 known as “E1.11 – 2008, USITT DMX512-A”, or just “DMX512-A”.
It soon became the primary method for linking controllers (such as a lighting console) to dimmers and special effects devices such as fog machines and intelligent lights. DMX has also expanded to uses in non-theatrical interior and architectural lighting, at scales ranging from strings of Christmas lights to electronic billboards.
A DMX512 network employs a multi-drop bus topology where devices are typically daisy chained after each other. A network consists of a single DMX512 controller – which is the master of the network — and one or more slave devices. DMX512 uses unidirectional variable-size packet-based communication protocol. At the datalink layer, a DMX512 controller transmits asynchronous serial data at 250 kbit/s. DMX512′s popularity is partly due to its robustness.DMX512 data is transmitted over a differential pair using EIA-485 voltage levels on cable with nominal characteristic impedance of 120 ohms. DMX512 does not include automatic error checking and correction, but due to cyclic constant transmission of all data errors due the interference are short temporary problems (just slight light flicker of noticeable at all).
The original DMX512 1990 specified that where connectors are used, the data link shall use five-pin XLR style electrical connectors (XLR-5). DMX512-A (ANSI E1.11-2008) defined the use of eight-pin modular (8P8C, or “RJ-45″) connectors for fixed installations. However three-pin XLR connector is commonly used for DMX512, on lighting and related control equipment, particularly at the budget/DJ end of the market (although that is specifically prohibited by section 7.1.2 of the DMX512 standard).
There is lots of information and project related to DMX512 in Internet. DMX-512 page from Ujjal website has been helping thousands of folks in understanding DMX512 since 1996.
There are some interesting open hardware projects on DMX512. Maybe the most popular is OpenDMX that is DMX512 master interface for PC. The Open DMX USB is inexpensive way to get into the world of controlling DMX devices from a PC. You can buy it as a ready made product or you can build one yourself. It is supported by many control software. It provides no-fuss control of 512 channels with full compatibility with a range of programs.Using a simple application on a PC you can send and also receive DMX512. It is very suitable for example for small live music applications.
Open DMX USB is an open USB to DMX hardware design developed by Enttec. The Open in Open DMX USB refers to the fact that everybody is free to use the design and produce its own USB DMX dongle without paying any licenses.This DMX USB interface is based on the FTDI 232RL chip, that a USB to serial converter. Basically the interface consists of FTDI 232RL chip and RS-485 transceiver chip. This interface design relies on the computer to handle all the timing of the DMX signal.
Here is my version of Open DMX USB design. I have built this many years ago and it has served me well.
Closer look to the electronics box.
Let’s look inside.
The circuit is built to a small piece of the prototyping board that host only the RS-485 transceiver chip. The USB-serial conversion part is handled by FTDI TTL-232R-5.0V USB- TTL Serial Cable based on FTDI 232RL chip, so all I had to add to it was MX483 chip that converts the serial data top RS-485. I also added few resistor to provide proper RS-485 line termination.
Other angle view.
Links to more information:
Other HW projects:
Your Arduino becomes a OpenDmx USB interface is a tutorial that explains how to use the Arduino as a USB to DMX interface for software that works with OpenDmx. Not that this design works only with an old arduino board that used FTDI chip, and the new Arduino UNO that uses different USB-serial chip (that is not compatible with this application)
DIY USB DMX Interface for under 10$ page describes how to convert a cheap RS485 USB converter to control DMX devices. Some cheap adapters can be used directly, some need some small modifications and some can’t be used. Be sure to get a converter that uses original FTDI chip and not any clones or completely different chips.
Links to software I have used:
Other interesting looking links: