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Thread: gsi 325dt galvo?

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    Default gsi 325dt galvo?

    Hi All,
    I'm a new member to this forum and I was wondering if any of you laserists out there have ever come across a General Scanning 325dt galvo? Would they be of any use for simple beam effects from a hobbist point of view? I'm also looking for a suitable driver amp circuit as I have a set of these galvos and I would like to put them to work! Any info much appreciated,

    Regards.
    Attached Thumbnails Attached Thumbnails GSI Galvo.jpg  


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    I used them a few years ago. They should manage a scanspeed up to 8 kpps with good drivers. I build drivers myself, but they only did 3 kpps. Every cheap chinese scanset can work faster then this old monsters. But you can put real big mirrors on it. Maybe you have an old copper-laser at home with 1 inch beam diamter ;-)

    All the best
    Karl

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    Thanks Karl, I thought they might go a little faster than that but I guess you're talking about 1980's technology here. Hopefully I can find a use for them...........close the front gates to my house perhaps.

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    Quote Originally Posted by helium View Post
    Thanks Karl, I thought they might go a little faster than that but I guess you're talking about 1980's technology here. Hopefully I can find a use for them...........close the front gates to my house perhaps.
    And throw away a 50' optical fairly fast scan angle for one axis beam effects on a 1" mirror? A g325 and 50 -100 mW in fog or haze in a private party situation can be very cool to have around if your a beginner. Keep it 3 meters up though, a 325 is nowhere near fast enough for scanning your audience.

    Even a L149 power opamp from electronic goldmine (a buck and change) can drive those, they are effectively a 7 ohm speaker.

    see attached, I cant draw, but that circuit is all you need to drive a g325Dt without the feedback but with damping, let me know if you want to use the feedback and I'll get you a real schmatic. You basically want a clone of a GSI A102 open loop amp. your looking at maybe 10$ in parts plus a +/- 12V 2 amp supply to drive that, cheap effect at the price. IF you google A102 and general scanning usually a link to the more complex PDF pops up. The A102 design can be considerably simplified by using a LM12, l149 or LM3886 as a driver stage and ditching the offset adjust circuits. The 50K pot and sampling network in the attached schmea provides just enough damping to be useful for beams with just a little ringing. Note it only works with galvos that have torsion bars , ie GSI products. If you were desperate, you could run the l149 power stage from 12V and use a 9V battery for the minus side of the opamp. Never, Never , Never , Trash a working scanner!

    Steve Roberts
    Attached Thumbnails Attached Thumbnails dampamp.bmp  

    Last edited by mixedgas; 04-11-2008 at 09:49.

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    Hi Steve,

    Thanks for that response. I have located the a102 circuit as you suggested but I would like to take a look at your closed loop schematic if you can dig it out for me. The galvos are in good condition and are complete with 1 1/4 inch dia mirrors so it would seem a shame to junk them as I am only going to use them for home use,

    Regards,
    Conor.

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    Conor,

    A while back I asked a friend to scan in the manual LM22SDA from the now dead Laser Media Co and the Cambridge Amp schematics and Manual, they kinda got mixed together, but the free hosting is appreciated and I never sorted it out. Ignore the cambridge schematics, they are much more complex then a GSI needs to be. But please read the cambridge tuning tips.

    You are perhaps best off to put a oscilloscope if you have one across the g325 feedback signals and input a square wave for the initial tuning. Adjust the controls for best square wave with the least ringing, and then go from there. If you feel up to doing DC coupling mods on a sound card, I could send you a wav file of a LM test pattern. I'm assuming you have no show software. Start by downloading a file called lissajous.exe :-) We'll talk about ways to make beam effects after that!

    so the manuals are here:

    http://www.skywise711.com/lasers/scanner/scanner.html


    I will scan the LM22SDA schematic and a GSI schematic and post them here, probably monday afternoon our time (its friday at 6PM here, I am off to home)

    I have not posted the LM22SDA amp schema in the PDF due to the fact with the faster G120 galvos, the LM22SDA can be a galvo killer if mistuned by someone who powers it up without reading the directions on "offset null" and "Inital Setup Potentiometer Settings". With the G325s, however it will be a good start and a G325 is very hard to kill as it cant move so fast as to kill itself by snapping the very thick flexure bearings in the 325. 325 is a little different then most GSI as it uses flexures for high precision instead of bearings and a torsion wire. It was used in old xray printers etc. where a highly parallel scaned beam was needed.

    Also please note the GSI older products use a RF feedback system that outputs very tiny currents, and is much, much different then the cambridge position demodulator. Each galvo gets fed very clean 12V that is current limited to run the feedback. If you go to www.uspto.gov, download the alternatif viewer and look at US pat number 5,099,386 and us pat # 04135119 you can get a idea of how it works. I would not use any component values stated in a GSI patent, wait till I can scan the drawings.



    cheers, Steve
    Last edited by mixedgas; 04-11-2008 at 14:19.

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    Default typical g325 etc pinout your milage may vary

    TYPICAL GSI DB15M connector

    please note that two cables go to one connector, colors are duplicated! the coil cables are obvioulsy the 4 wire one and unles syour making a xray film printer, you dont need the heaters and thermister ;-)

    Pin Number Wire Colour Signal Description
    1 Red Drive Coil (See notes 1 & 2)
    2 Yellow Drive Coil (See notes 1 & 2)
    3 Black Position output (-)
    4 Orange Position Output common
    5 Red Heater - T-Type (See note 3)
    6 N/C No Connection
    7 Red Heater - T-Type (See note 3)
    8 White Oscillator supply voltage (+)
    9 Green Drive Coil (See notes 1 & 2)
    10 Black Drive Coil (See notes 1 & 2)
    11 Red Position Output (+)
    12 Violet AGC Output
    13 Brown Oscillator supply voltage common
    14 N/C No Connection
    15 Blue Thermistor - T type (See note 3)

    NOTES

    1/ To wire drive coils in series, connect Black to Green and drive Red to Yellow. Series wiring is recommended for use in position sensing (closed loop) mode.

    2/ To wire drive coils in parallel, connect Red to Green and Black to Yellow. Use parallel wiring only when driving the galvo in open-loop mode.

    3/ Heater blankets are mounted only on the G120DT type galvos and are not commonly used in light show applications.

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    Hi Steve,

    Again I must thank you for your helpful and detailed response to this post. Previously I couldn't find anything regarding the g325 on the net. Well I do have a scope so I can test the feedback response of the galvo once I can decide on which amp to build. You're right about me not having any show software but I hope to use Norms USB DAC and software when he gets it sorted. The only method I have of driving an amp at the moment is with a sine/cosine cct. I built using a Burr-Brown 4423 chip but I could have a go at modifying a sound card to generate your test pattern. Looking forward to seeing those schematics,

    Best Regards,
    Conor.

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    Conor, Enjoy :


    BTW, this is not the laser media amp, this has a litttle more quality to it.
    File is attached, SCANAMPg325.pdf


    btw, where in the heck did you find a 4423 in this day and age?. I have one in the collection.



    Steve
    Attached Thumbnails Attached Thumbnails SCANAMPg325.pdf  


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    Steve,

    I got the 4423's and built the sine/cosine oscillator cct. about 12 years ago, around the time I got a secondhand Argon tube. The deal with the tube at the time was you basically just bought the tube and you had to make the power supply and other bits 'n pieces yourself. Worked fine and kept the room warm. Haven't seen it for years though, it's under a pile of junk in the shed....I'm building a uv light box at the moment so hopefully I can make my own PCB's and get those galvos working,

    Regards,
    Conor.

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