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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.

William R. "Bill" Benner, Jr.
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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