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Laser
F/X On-line Newsletter - Special Reports
DMX
Seminar Handout
15:00 to
16:30 - Seminar 3 - DMX for Dummies
Bill Benner of Pangolin Laser Systems, chair of the ILDA
tech-Com, and one of the drafters of the ILDA DMX standard, provided the
handout reprinted below at the DMX seminar.
| About The
Author
Laser light show software programmer, hardware design engineer
and industry entrepreneur, William R. "Bill" Benner, Jr.,
has been actively delivering product to the industry since 1989. His
patented hardware designs and software products have revolutionised
the component technology and show design programs available to laser
light show producers today. And he has led or collaborated on all
the major products which are the foundation of this industry.
Bill has been active in the laser display community since 1985, from
his start as the Laser Technician at the Daytona Planetarium,
through his current roles as Vice President of Engineering for
Pangolin Laser Systems and Chairman of the International Laser
Display Association (ILDA) Technical Committee.
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Bill is a consultant to the industry, working with show
producers on specific projects, as well as manufacturers including
NEOS Technologies, MediaLas, General Scanning and RMB Miniature
Bearings.
He has had articles published in the SMPTE Journal, The Laserist,
LaserFX, EDN magazine and Motorola's Embedded Connection magazine. He
is widely recognised as an expert in the field for hardware design and
for programming in Visual Basic, Visual C++ and Assembly language for
most modern microprocessors. |
DMX512
Workshop - Laser F/X 2000 Conference
Burlington Ontario, Canada
DMX512 Background
DMX512 History
- DMX512 is a digital-multiplexed lighting communications standard.
- DMX512 was created in 1986 by the USITT as a standardised method for
connecting lighting consoles to lighting dimmer modules. It was revised
in 1990 to provide more flexibility.
- The DMX512 standard is currently controlled by ESTA, as standard BSR
E1.11 - the DMX512/2000 standard.
- It's the most common lighting equipment communication standard.
DMX512 Specifics
- DMX512 provides up to 512 control "channels" per data link.
- Each channel contains an 8-bit number having a value between 0 and
255.
- DMX512 supports multiple receivers, connected using a daisy-chain
connection methodology.
- Up to 32 receiving devices can be present on a single DMX link.
DMX512 Internals
- Data is transmitted serially, at 250,000 bits per second over two
wires plus a cable shield.
- DMX512 uses a simple protocol consisting of a reset condition, a start
code, and up to 512 bytes of data.
- Data packets are transmitted continuously - one right after the other.
Common DMX Devices
- DMX Dimmer Packs: Have a fixed number of dimmer
channels and AC outlets into which you plug the light fixtures.
- DMX to Analogue Converters: Have a fixed number
of output channels, usually between 8 and 32 per converter. May use a
jumper or potentiometer to adjust the output voltage range from 0 to 5V
up to 0 to 10V.
- DMX-to-TTL Converters: Output is at TTL-compatible
voltage levels. These converters may offer more channels and a lower
price than DMX-to-Analogue converters.
- DMX-to-Relay Converters: Have a fixed number of
relays.
- Intelligent Lighting Fixtures: Use between 6 and
24 DMX channels to control brightness, colour, focus, gobos, beam shape,
and other parameters of the lighting fixture.
- DMX-controlled Laser Projectors: Laser projector
must have a DMX-to-Analogue converter within the projector. This
converter is connected to control various laser projector functions such
as:
a/ Beam actuators that can fade beam positions
b/ Shutters and filters that can gradually occlude the beam
c/ Lumia motor speed
d/ Rotating diffraction grating selection
e/ Rotating diffraction grating speed
Potential DMX512
Gotchas
- 3-pin vs. 5-pin Connectors: 3-pin XLR connectors are used instead of
5-pin XLR connectors on some older fixtures. To make a 3-pin to 5-pin
adapter, connect pin 1 of the 3-pin connector to pin 1 of the 5-pin
connector, pin 2 to pin 2, and pin 3 to pin 3.
- Data Link Termination: The end of the cable must be terminated by
connecting a 120 ohm resistor to pins 2 and 3 of the DMX connector.
- Refresh Rate Too Fast: Very few DMX devices can actually work with
full bandwidth DMX. - If your DMX device is not receiving DMX or seems
intermittent, you should try to increase the packet-to-packet delay or
increase the number of channels transmitted.
- DMX512 Data Link reliability: The receiver can "drop data
bits" in a channel or channels. The receiver can "drop
channels".
Dropped bits rarely occur and dropped channels almost never. Combined
with the "continuous transmission" aspect of DMX512, data link
errors are essentially a non-issue.
Improved Data Link
Reliability with the New "System Information Packet" (SIP)
The new BSR 1.11 - DMX512/2000 specification provides for a System
Information Packet (SIP), which includes the following information:
a/ Checksum of the last packet
b/ Number of channels in a standard data packet
c/ Other information including sequence numbers, software revisions and
test information
- SIP can be used to improve data integrity if both the controller and
devices support the SIP.
- SIP would typically be "interleaved" with normal data
packets.
DMX512 Compared with
Other Possible Control Methods, such as MIDI
When considering possible laser projector control schemes, think about:
- The cost of implementation and use
- The availability of devices -- consoles, PC add-in boards, devices,
software, etc.
- Ease of installation and use
- The relative ease of designing and creating in-house devices yourself,
such as boards
- Recordability
- Safety
- Fault tolerance and recovery
The usable communication distance The DMX512 protocol is superior to MIDI
and other protocols in all of these aspects.
DMX Output from the
QM2000
- The QM2000 board has an on-board DMX port.
- No additional PC hardware is needed to output DMX from any program
that uses the QM2000
Presented by: William R. Benner, Jr.
Pangolin Laser Systems
771 South Kirkman Road, #113, Orlando, FL 32811
Phone: 407-299-2088, Fax: 407-299-6066
E-mail: bill<at>pangolin<dot>com
DMX Resources
http://www.pangolin.com/LD2000/dmx-about.htm
These pages are an expanded, updated version of Bill's notes,
complete with pictures of DMX connectors etc.
http://www.usitt.org/
The home page of the USITT who Maintain the DMX 512 standard.
Click the DMX512 button for information.
Quick Links to Report
Pages
In order to present as many pictures
as possible, we have broken this special report down into a number of pages
to speed access. Most of these are large pages with many images so please be
patient while they download.
Laser
F/X 2000 Report -
Introduction and background
Friday
19 May - Behind
the scenes
Saturday
20 May - The
Pangolin School and Open House
Sunday
21 May A -
Seminars
DMX
Seminar Handout -
By Bill Benner
Sunday
21 May B -
Brewster Awards
Monday
22 May - Trade
Show and LaserFest
Candid
Camera - A
selection of 12 photos (very large page)
DISCLAIMER:
Some of the information in the Backstage area is provided by the
persons or companies named on the relevant page(s). Laser F/X does
NOT endorse or recommend any products/services and is NOT
responsible for the technical accuracy of the information
provided. We provide this information as a service to
laserists using the Backstage area.
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