Results 1 to 3 of 3

Thread: Beam positioning with GM20's ?

  1. #1
    Join Date
    Jul 2007
    Location
    Knoxville, TN & Huntsville, AL, USA
    Posts
    3,108

    Default Beam positioning with GM20's ?

    I have a couple of GM20's enroute to me that I hope to incorporate into my projector - I plan on using them for beam shutter and beam positioning control.

    Since I don't really need a variable input signal to drive them, I was thinking about using a fixed voltage input with a trimmer potentiometer to adjust the desired deflection / beam position.

    Would my idea work, and if so, what is the max input voltage that could be safely used without damaging the GM20? In lieu of my idea, could anyone recommend a simple driver circuit that would provide the same results? I really want to try to avoid "cooking" any components if possible!

    Thanks!
    RR

    Metrologic HeNe 3.3mw Modulated laser, 2 Radio Shack motors, and a broken mirror.
    1979.
    Sweet.....

  2. #2
    mixedgas's Avatar
    mixedgas is online now Creaky Old Award Winning Bastard Technologist
    Infinitus Excellentia Ion Laser Dominatus
    Join Date
    May 2007
    Location
    A lab with some dripping water on the floor.
    Posts
    9,012

    Wink

    GM20s have a roughly 7 ohm impedance, the same as a small loudspeaker.
    traditionally they are driven one of three ways

    I. a roughly 12V source and a NPN transistor, with the NPN in series with the GM20, with the base of the transistor driven via TTl signals with a limiting resistor in the base circuit. A reverse biased diode is placed across the GM20 to prevent inductive spikes from damaging the circuit when the transistor is turned off

    II. A constant current source , this causes less heating of the GM20 and prevents slamming against the internal stops, the GM20 lasts much longer, moves faster and effects are much cleaner as there is no "ringing" in the motionI can send you a simple schmatic for this, but I cant post it (proprietary design) You can buy these from Precision Projection and Logic Systems Design.

    III a analog DC coupled audio amplifier see
    http://www.gs-scanners.com/pdfs/manuals/A102_AX200.pdf
    (General Scannings A102)
    for a rather complex schematic with damping, but that one will maximize your performance. Sadly that needs split supplies.

    iv, A ORDINARY STEREO, BUT HAS NO dc CONTROL

    sTEVE rOBERTS
    Last edited by mixedgas; 08-23-2007 at 08:25.

  3. #3
    Join Date
    Jul 2007
    Location
    Knoxville, TN & Huntsville, AL, USA
    Posts
    3,108

    Default

    Good info, as always - thanks!
    RR

    Metrologic HeNe 3.3mw Modulated laser, 2 Radio Shack motors, and a broken mirror.
    1979.
    Sweet.....

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •