Protocols Revisited - Making Things Talk - page 431

DMX512
DMX512 is another binary protocol worth knowing about.
It's a real-time serial protocol for communicating between
stage-lighting control systems and lighting dimmers. It has
been the industry standard for stage lighting and show
control equipment for a couple of decades now. It's also
used to control special-effects machines, moving lights,
projection systems, and more.

few shields on the market that have DMX connectors
on them. I've only tested two personally, both of which
work well: the Tinker DMX shield is available from the
Arduino Store at http://store.arduino.cc/ww/ , and Daniel
Hirschmann's Super DMX shield is available from http://
www.hirschandmann.com/2011/super-dmx-shield-for-
arduino/ . The former lets you add your own connector; the
latter has XLR, RJ-45 connectors, and terminals for you to
add your own. Further notes can be found on the Arduino
playground site at www.arduino.cc/playground/Learning/
DMX . For more on DMX, see www.opendmx.net .

DMX512 uses the RS-485 serial protocol as its physical
layer. RS-485 is a bus-style serial protocol, meaning you
can have several devices sharing the same transmit and
receive lines, as long as each has a unique address. It
uses differential signaling so that signal wires can be very
long—up to 1200m. DMX512 devices generally use an
XLR-style connector, either three pin or five pin, though
many devices now use an RJ-45 Ethernet-style connector.

Like MIDI, DMX is an aging protocol. The lighting industry
has started to develop its successor, Advanced Controller
Network, or ACN, which can run over Ethernet. Over the
next few years, you can expect to see it grow in promi-
nence. For more on show control protocols in general, John
Huntington's book Control Systems for Live Entertain-
ment (Focal Press) can't be beat.
X

At 250kbps, DMX512 is fast for a serial protocol; it's fast
enough that you can't just send it as regular TTL serial
data from a microcontroller. However, there is a DMX
library for Arduino called Simple DMX, and there are a

Figure 11-6
Tinker DMX shield, left, and Daniel Hirschmann's
Super DMX shield, right. Both allow you to commu-
nicate with DMX512-based lighting and show control
systems.