Some real work for the Arduino and Pi – DMX Lighting
In a previous article we briefly touched on DMX lighting – Light Control – The DMX system . Lighting control has been with us for eons and where there is sound there should always be light, right? But first things first.
The DMX controller is very versatile, modern units have large memory reservoirs to control lighting automatically for almost every theme and scene. Smaller units are available for the DJ scene and pack the power of old analogue lighting controls used for supergroups years back.
Most audio equipment at home draws very little current from the mains supply. As we go up the pecking order we have amplifiers which can draw in excess of 20A from 220V which usually attracts the neighbours and police and then we have the juggernauts, arrays being driven by over 100kW of power amplifiers. Sound like a lot of power? Well, think of the light show.
Lighting can easily draw more than your entire audio equipment. Many big bands prefer to supply their own generators and electrical engineer. The reason for this is three-fold – under capacity at the venue, poor voltage supply which can damage expensive (read: very expensive) equipment and of course the electrical engineer and electricians need to be qualified to fix problems, and rapidly. There are other reasons as well – mainly redundancy.
Before our young DIY experimenters dive onto their clock pulses beware of the most fundamental reason for electrocution: carelessness. We cannot emphasise enough the dangers of working on mains and/or live equipment without having the ability or knowledge. Those that die of it seldom recover.
Lighting and control systems as a rule should always have some form of isolation between the analogue and/or digital controllers and the lighting supply which is usually single or three phase power.
To switch a 220V light bulb on and off we can use a standard light switch, a relay (which isolates the actuator coil and circuit from the mains) or the more common triac. See SCR (Silicon Controlled Rectifier) circuits in previous article. Of the latter two circuits the triac is preferred due to switching speed and of course, no moving parts.
The DMX Controller
DMX512 data is transmitted as two complementary signals often through a twisted pair, known as a differential pair, using RS-485 voltage levels over a serial communications system.
Daisy chaining from controller to slave devices are common. Limitations are usually given in the controller specification sheet. See Obey 40D-Fi 2.4 image above and marketing spec below.
Obey 40 D-Fi 2.4
The Obey 40 D-Fi 2.4 is a small, but full-featured lighting controller with a built-in D-Fi transmitter so you can built a rig without long DMX cable runs! The Obey 40 D-Fi 2.4 works with any D-Fi compatible product and controls up 12 different types of lights. It stores scenes and chases for playback, and it operates lights “on the fly”. The stored scenes and chases are triggered by sound, or manually adjusted, to get just the right speed and fade time for your look. The Obey 40 D-Fi 2.4 is MIDI compatible and has dedicated fog and strobe controls. The Obey 40 D-Fi 2.4 is the perfect board for creating a dazzling light show without long cable runs!
Arduino already has a shield ready for this purpose: (available on eBay).
Make your own PIC 16F84 64 channel controller
ePanarama has a simple PIC 16F84 64 channel DMX512 controller – see here. Circuit page includes a splitter/booster using SN75176A Differential Bus Transceiver.
RS485 RS422 Transceivers
A very popular RS485 traceiver was the MAXIM485 (The MAX481, MAX483, MAX485, MAX487–MAX491, and MAX1487 are low-power transceivers for RS-485 and RS- 422 communication)
Toni Morino – deskcontrolnet – Arduino Uno – Mega used as DMX controller.
DMXshield – A 2.5kV power isolated shield for Arduino
DMX controlled water cooler.
Raspberry Pi light show – using the Velleman K8062. Although the K8062 kit is rated very highly the performance lacks somewhat. Be familiar with the upgrade which is available – solution is drop in and up to 80 times faster than the legacy PIC.
The Velleman K8062 schematic.