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Laser Show Systems - System Design

Compact Programming System
By L. Michael Roberts


The design of a practical, compact 30K laser graphics programming system based on a modulatable red diode laser and 6800HP scanners is described.  A secondary design criteria was to allow the use of the programming projector with an external laser source.



For programming laser graphics and animations, it is often impractical and can be expensive to set-up a whitelight laser.  It is not always necessary to see the images in colours as during digitizing and programming, the quality of the image, sharp corners, joined lines and the overall 'look' of the image are more important considerations.  The design objective for this system was to create a programming projector based on a diode laser, but with sufficient flexibility that it could be used with other lasers of various types as well.


Design Constraints

The major constraints in terms of size were; all the components that had to fit into the case [no outboard electronics], and the case had to be an 'off the shelf' enclosure to save the expense of having a custom enclosure manufactured.
The single largest component of the system was the +/- 24 VDC regulated power supply needed for the scanners.  The second largest component was the scan amps themselves with all other components having much smaller footprints.
The input connector chosen was an DB25 ILDA standard connector so as to have maximum compatibility with a variety of graphics and control systems.

The completed projector in use with an external whitelight laser and PCAOM
The completed projector in use with an external whitelight laser and PCAOM



The enclosure chosen was an 'off the shelf' electronics cabinet available from a local electronics store.  The cabinet was made of thin formed steel with aluminum front and back panels and measured 16 X 12 X 6 inches [40.5 X 30.5 X 15.5 cm].
The cabinet was not sufficiently rigid to mount optical components in a stable relationship to one another.  A 1/4 inch [.7 cm] baseplate with the same depth as the enclosure [12" - 30.5 cm] and extending 1.75 inches [4.5 cm] beyond one end of the cabinet was attached to the bottom of the cabinet.  This provided a firm foundation for mounting the power supply and other components and also provided rigidity for the optics.
In order to provide maximum flexibility and configurability in mounting the optics, a 'mini' optics plate measuring 10 X 6 inches [25.5 X 15.4 cm] with holes tapped 1/4-20 on a 1 X 1 inch [2.5 X 2.5 cm] grid was mounted to the font right quadrant of the projector.  This would allow for the mounting of the diode laser, scanners, steering mirrors and an optional PCAOM cell if full colour operation with an external laser was desired [the PCAOM driver would have to be in an outboard enclosure in this configuration].
The power supply was bolted to the aluminum baseplate through the cabinet at the far left hand end of the enclosure.  In order to save space, a small PSU board with caps and +5 VDC regulator was mounted inside the 24 VDC power supply and fed from the positive rail to provide power to the red diode laser. The scan amps were mounted at the back right hand side of the cabinet so that the trimmer controls faced outwards and were easily accessible with the cover off.
The CTI 6800Hp scanners were installed on the standard Cambridge Technology heatsink.  This in turn was mounted on a black anodized L bracket made of 1/4 inch [.7 cm] aluminum.  Heat transfer compound was used at the junction of the CTI scanner heatsink and the L bracket to insure good thermal transfer.  The L bracket was drilled and tapped with the hole on the optical axis of the input beam.  This allows the entire scanner set on it's L bracket to be adjusted for vertical image placement.  This assembly was attached with a single screw to another L bracket with slots in the base designed to pass 1/4-20 screws so that it could be optimally placed and adjusted into the laser beam.



The photo below shows the completed projector with the components numbered and the laser path drawn in red for clarity.

The assembled programming projector shown with the top cover off
The assembled programming projector shown with the top cover off.

  • 1/  The regulated +/- 24 VDC power supply for the scanners.  At the front left side you can see the top of the circuit board for the +5 VDC laser power supply.

  • 2/  ILDA format DB25 input connector on the back panel for the scanning signals

  • 3/  Input gain control pots to adjust mage size

  • 4/  Cooling fan for the scan amps.  This is a 24VDC fan which was connected to the negative side of the supply to balance the load as the laser is powered from the positive side of the supply.

  • 5 & 6/  A pair of single channel DLT 9370 scan amplifiers from new Method Lasers. Note that the adjustment trimmers face outwards for tuning the system.

  • 7/  The extension of the baseplate with two tapped 1/4-20 holes. This is provided so that the projector can be used with outboard lasers by sending the beam through a hole in the side of the cabinet.

  • 8/  The mini optics plate tapped with 1/4-20 on a 1 X 1" grid for mounting the optical components - there is sufficient additional space on the right side of the plate for input steering mirrors and a PCAOM cell if desired.

  • 9/  A Spectronika optics post and post holder mount holding a 30 mW modulatable red laser diode [brass barrel] from New Method Lasers which is powered from the +5 VDC PSU.  The modulation input is connected via a diode array to the ILDA DB25 connector - the diode array combines all of the 6 colours into one signal.

  • 10 & 11/  A pair of Spectronika OM3/4 optics mounts with post and post holders.  These hold mirrors to steer the laser beam into the scanners.

  • 12/  the CTI 6800Hp scanners mounted on a standard CTI heatsink and then on an L bracket to allow for vertical adjustment - the adjustment screw can be seen on the left. That assemble is mounted on a secondary L bracket with slots for adjustment into the laser beam. [The large coil of cable to the right is the standard length of cables as provided by CTI.  the author left them intact to avoid cable capacitance issues.]



The author would like to thank Bob Ash of New Method Lasers who provided the +/- 24 VDC PSU, modulatable red diode laser and the DLT scan amps, and also provided technical assistance in tuning the system.


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