"This document describes a project I undertook and discusses
the reasons why I felt that designing and constructing
my own was preferable to buying a commercial unit"

During my investigations of existing lighting control units I was disappointed to find a total lack of imagination and flexibility in the way light channels were controlled. Commercial units only seem to use MIDI Note-On messages to extract the light channel and intensity values.
 

Using this Note-On strategy also prevents the MIDI port from being used to drive other sound modules etc. as notes will sound. I found creating sequences with Note-On data within a sequencer's graphics editor extremely difficult. The commercial units also come with internal preset light sequences which aren't modifiable.

The Hardware

I have implemented a 12 Channel System capable of delivering 300 Watts per channel. A Motorola 68HC11 Microcontroller was used to receive the MIDI messages and write them into an Altera 8254 Field Programmable Gate Array (FPGA) device. This device has a circuit configured within which generates the control triggers for the triac devices. These control the lamps' to give 128 intensity levels.

MIDI Control

The control of light channel selection and intensities was achieved using Unallocated MIDI Controllers. For example, these messages can be generated by Cubase's MixerMaps, (using faders) List or Key Graphics Editor. The result is light sequences or patterns that can be saved for insertion into musical arrangements later. The patterns can then be trimmed in length, or compressed in time etc. - basically any manipulation the sequencer's editor(s) allow.

Light Level Control

Each light channel has 3 MIDI Controllers that affect it.

• Channel Level (Nos:- 20 to 31)
• Channel Gain (Nos:- 52 to 63)
• Master Gain (No:- 15 )

is used to generate the patterns as described above. The full 0 to 127 value range is used but as we will see later (in Master Gain) the 127 value doesn't necessarily mean full brightness.

is used as presets to offset certain channels that appear brighter than they should. Coloured filter gels absorb different amounts of light depending on its colour. Blue, for instance, will absorb more light than yellow.

is used to control ALL the channels overall intensity. This can also be used to generate Light Accents in time with the music beat. The example below would give the lights a more closer association with the music's feel.

A Future Product

For upward compatibility the Note-On message strategy would also be incorporated as well as my Channel Level Controllers method. Using an FPGA device reduces the overall component count and costs. They can be used to expand the number of channels by plugging in larger capacity devices into the same socket.

Having lots of low power light channels enables much more creative, complex and dynamic effects to be produced. Lighting rigs are expensive, but by using ordinary 100 Watt Spot Lights, a large array can be constructed cheaply.

User Applications

• Select from 100's of sequences available and create a light pattern track on either their own or purchased MIDI Files. The patterns then playback in time with the music.

• Use Cubase MixerMaps to set up static scenes and save them as snapshots.

Cross Patterns...

The $64,000 Question:- Does this prototype have any Market Potential?

A summary of the facts:-

• Versatile MIDI control
• Reduced component count and costs
• Channel Expansion capability
• Potential as a Kit Version
• Industry Standard DMX512 Interface support (for dimmers) using spare FPGA capacity
• Possible support by MIDI File creators to generate the Light Tracks for the customers
• Use University facilities for the product design i.e. PCB, FPGA, ASIC and software.

Please contact me if you have any questions, comments or require more information.

Harvey Twyman,
Digital Systems Laboratory,
Department of Electronics,
University of Kent.
Canterbury.
Kent. CT2 7NT

Tel: 01227 823198
Email: harvey_twyman@yahoo.com