What is DMX-512?
DMX-512 is the predominant theatrical lighting control protocol used in theatrical and architectural lighting control devices worldwide. DMX-512 has been in use since 1990. The protocol is so common that most dimmers produced today are manufactured DMX-512 compatible.
There are dozens of manufacturers producing DMX dimmers from simple single channel 500-watt dimmers all the way up to 96 channel dimmers that can control over 200Kw of lighting load. DMX-512 can simultaneously control up to 512 channels of lighting control - this group of 512 channels is generally referred to as a ‘DMX universe’.
DMX-512 signals are traditionally carried by RS-485 twisted pair cables from transmitting devices to receive devices. DMX is transmitted at 250Kbaud with a maximum update rate of 44 times per second with 512 channels.
DMX-512 transmitting devices are mainly theatrical memory consoles with manually operated faders used to program presets that are recalled by button press or automated sequence.
DMX-512 receiving devices are mainly lighting control dimmers, RGB LED fixtures or moving light fixtures that read the DMX-512 transmitted signal and interpret the information as lighting levels, color hue or fixture position.
Wireless Control of DMX
The term wireless DMX usually refers to replacing the existing RS-485 DMX cables with a suitable wireless RF link.
This requires a continuous RF signal usually utilising spread spectrum techniques. There are a number of manufacturers that already produce this type of wireless RF DMX link.
However, a wireless RF DMX transmission link is not what we’re referring to in this article. What has been implemented here is a method of DMX-512 ‘translation’ using the wireless UHF EnOcean protocol via the PTM based telegrams from momentary contact switches, though all EnOcean telegrams can be supported by this RF interface.
This system has two main components: the wireless interface/controller and the PTM switches. The PTM switches transmit standard wireless EnOcean telegrams which are received and processed by the interface, which then translates the received information into an industry standard DMX-512 data stream.
The DMX data is then connected to any industry standard DMX device (usually a dimmer) where the DMX signals are interpreted and output as lighting levels.
Functionality of the Control Interface
Current controllers have three modes of operation: a basic up/down dimming mode, an economical pre-programmed preset recall mode and the programmable ‘snapshot’ mode.
Up/down dimming mode: this is the simplest Interface mode. The PTM switches function as manual dim up or dim down controls when pressed. Each press of the button smoothly dims up or down the pre-configured DMX control channels in increments of 10%. Each button can control up to 48 DMX channels.
Pre-programmed preset recall mode: this is the most economical Preset Recall mode. Factory programmed scenes (combinations of lights and levels) are stored in the Interface and recalled by PTM pushbuttons with a three second fade between scenes. Each button can control up to 48 DMX channels.
Programmable DMX snapshot mode - the Interface when used with any industry standard DMX-512 controller or console can store ‘snapshots’ of scenes set up by the DMX controller for recall by PTM control stations.
These scenes are repeatable lighting ‘looks’ created by adjusting DMX lighting control channels to create the desired combination of lights and levels. The number of DMX control channels per scene can be up to 512 channels.
The fade time between scenes is a fixed three seconds (the fade time is factory adjustable). Scenes can be modified live by an up/down master PTM switch in 10% increments.
PTM control stations are available with two, four or eight scenes. Multiple DMX ‘universes’ are possible using separate interface modules. The DMX interface has fully bi-directional communication capability for future use with RDM compliant devices. The interface is available in high and low voltage (class 2) versions.
A benefit of using wireless technology is that the information sent by devices is accessible anywhere in a room or space, not just along the wires. So components can be optimally positioned without concern for existing wires or the difficulty in getting wires to certain locations.
It also allows a simple and cost effective method of upgrading and expanding current DMX based lighting control systems which are often located in large and extremely hard to wire buildings. Combining a wired DMX system with EnOcean wireless components allows an installation to benefit from both technologies.
Where do we go from here?
The addition of more wireless signal sources will allow for a wider variety of lighting control scenarios implementing devices such as photo sensors, occupancy sensors and time-based devices.
This research paper is kindly reproduced with permission from the Enocean Alliance. For more information check them out online at www.enocean-alliance.org
There has been an increasing number of DMX-512 devices being released to market in recent years. The protocol has also been adopted by various industry organisations as an official standard, including the International Laser Display Association, despite the fact DMX-512 controlled laser products remain scarce on the market.
Established technologies leveraging the DMX-512 protocol include:
- Lighting dimmer packs.
- DMX to analogue converters.
- DMX-to-TTL and DMX-to-relay converters.
- Intelligent lighting fixtures.
DMX-512 FAST FACTS
- The DMX-512 communications standard covers digital multiplexed signals.
- DMX-512 was created in 1986 by the United States Institute for Theatre Technology (USITT). It was revised and refined in 1990.
- It is the most common standard used in theatre and architectural lighting control applications.
- As the name suggests, DMX-512 provides up to 512 control ‘channels’ per data link.
- Serial data can be transmitted at distances up to 4000 feet over microphone-like cables.
- DMX-512 data is transmitted at 250,000 bits per second using the RS-485 transmission standard over two wires.