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Thread: Tiny projector build

  1. #1
    Join Date
    Apr 2010
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    San Francisco
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    215

    Default Tiny projector build

    Along with the j4cDAC, I've been working on my first projector build, and it's now getting pretty close to done...



    More photos of the case here.

    It's tiny - 6" by 8" by a bit over 3". Inside is a "200mW" green pointer core from eBay, two LOCs, a blue diode, a set of PT-30k galvos, and a j4cDAC.

    Here's what it looked like before I built a case around it:





    The driver board is three simple opamp-and-BJT high side CCSes, plus a TI buck converter module to provide a 6.5v rail for the diodes from the main 24v power supply. I built it from scratch on some perfboard.



    There is no mains inside the projector. A small laptop-type power supply provide the main +24v supply, which powers the diode driver board, DAC, and galvo drivers. Additionally, a DC-DC converter provides the -24v galvo supply. This lets me keep most of the PSU bulk encapsulated and saves a lot of space. I'd really like a galvo driver board that drives the galvo coil push-pull with an H-bridge arrangement from one rail, but oh well.



    There's a cutout in the bottom of the baseplate to facilitate messing with the mirror adjustment screws. It's covered with a piece of plastic in the assembled projector.



    Here's a closeup of the diode module. The LOC diodes are in dave's mounts, modified for isolation (I posted a thread about it). Green is in a cut-out clamp, and blue is in an unmodified dave mount. The PBS was provided by swamidog, and comes from a LaserDisc player. (Swami, I still owe you some mirror mounts. Thanks!)

    Most of the construction photos are a bit old. I've flattened out the lasorb assemblies and diode wiring, so the highest point off the baseplate is now the edge of the galvo drivers and the connectors on the j4cDAC.

    The thread would not be complete without photos of light coming out of it. Here are some beam shots in fog -




    And, last night we got some video of it running dchammonds' abstract generator:

    http://www.youtube.com/watch?v=3sMZIQU8SiQ

    Now I'm debating spending some cash on a 637nm diode...

  2. #2
    Join Date
    Oct 2006
    Location
    Central Florida
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    7,067

    Thumbs up


    ...............
    Love, peace, and grease,

    allthat... aka: aaron@pangolin

  3. #3
    Join Date
    Sep 2009
    Location
    Mexico
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    474

    Thumbs up

    I like your set up.

    Very compact.
    And mounted on a tripod awesome.

    Cheers,
    Ed

  4. #4
    Join Date
    Dec 2008
    Location
    Southport, UK
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    2,746

    Default

    That is a cute clever build
    http://img62.imageshack.us/img62/3985/laser.gif

    Doc's website

    The Health and Safety Act 1971

    Recklessly interfering with Darwinís natural selection process, thereby extending the life cycle of dim-witted ignorami; thus perpetuating and magnifying the danger to us all, by enabling them to breed and walk amongst us, our children and loved ones.





  5. #5
    Join Date
    Nov 2010
    Location
    Denmark
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    244

    Thumbs up

    Nice build!

    I have also been planning something like this as my next build.

    Where did you get the 24V to -24v dcdc?

    I ended up building my own last time i needed one...

    The vertical beam table is a great idea - saves a lot of space

    /Thomas

  6. #6
    Join Date
    Apr 2010
    Location
    San Francisco
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    215

    Question

    Thanks!

    The DC/DC converter is a Mean Well PSD-30B-24. Mouser carries them. It's rated at 1.25A output; the PSU that came with my galvos is rated at 1A per rail, so the new one is plenty. Different galvos may need more, though.

    The trick is to use an isolated converter and wire up its positive output terminal to ground. Then its output negative side provides -24v. The layout is like so:



    The laser driver module uses a TI PTN78020 to give me an intermediate rail suitable for the diode CCSes.

  7. #7
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    Nov 2010
    Location
    Denmark
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    Default

    Quote Originally Posted by j4cbo View Post
    Thanks!

    The DC/DC converter is a Mean Well PSD-30B-24. Mouser carries them. It's rated at 1.25A output; the PSU that came with my galvos is rated at 1A per rail, so the new one is plenty. Different galvos may need more, though.

    The trick is to use an isolated converter and wire up its positive output terminal to ground.
    Clever solution - didn't think of using an isolated dcdc - only downside is their size... 100x50 mm is huge, put next to the 40x40mm nonisolated inverter i built.

    On the other hand, M.W. supplies are dead cheap - ~16 euros won't even get you the pcb for a diy design

    /Thomas

  8. #8
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    Default

    Yeah. What I'd really like is a full-bridge galvo driver that doesn't require a negative rail (instead driving both ends of the galvo coil), but I don't think any such thing exists...

    TI has some negative-output POL modules, but they only go up to -15v.

  9. #9
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    Nov 2010
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    Denmark
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    Default

    Quote Originally Posted by j4cbo View Post
    Yeah. What I'd really like is a full-bridge galvo driver that doesn't require a negative rail (instead driving both ends of the galvo coil), but I don't think any such thing exists...
    True - something like a TDA7391 would do nicely as a galvo driver:
    http://www.st.com/internet/automotive/product/65194.jsp

    Quote Originally Posted by j4cbo View Post
    TI has some negative-output POL modules, but they only go up to -15v.
    I know - that is where I stranded last time I was searching, and ended up building my own around a LT1074HV... If only I had thought of the isolated dcdc idea back then

    /Thomas

  10. #10
    Join Date
    Aug 2008
    Location
    Berkshire
    Posts
    661

    Default Re: Tiny projector build

    That's a really excellent build. Very clever optics arrangement. Did you use the same tape used in dave's mounts to isolate the your green?

    Adrian

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