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Thread: WTB : First set of Dichros

  1. #1
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    Default WTB : First set of Dichros

    Hi All,

    I'm after my first set of dichros for an RGB build using the new 445nm blue and GGW, Red diode(s).

    I first planned to simply use sled optics as size is everything but if I can get small enough dichros these would obviously do a better job with less losses and give more flexibility with module arrangement.

    At this stage I'm not looking for massive quality and can even consider damaged ones as no mounts will be used for them. This may seem primitive but the personal challenge on this build is the tiny scale. This should end up a projector in your pocket using the stepper motors from the GGW sled also. I know, I know, a stepper build is intially a laughable project and nothing ground breaking but it is a educational, novelty build and does anyone know of cheap useable galvos no bigger than 10mm in any direction?!

    I hope someone can help me out.

    Thanks all,

    M

  2. #2
    Join Date
    Dec 2009
    Location
    Devon
    Posts
    48

    Default

    Hi,

    I'm probably not the best person to ask about where to buy dichros, but for small galvos you could try finding some older barcode scanners? They used to use small mirrors in them which sat on springs and were scanned with a small coil.

    Not sure about 10mm galvos, but the mirrors could be made even smaller than the sled steppers. I'm assuming that all laser galvos will be MEMS based in the future?

    Those would be better than steppers (for simple graphics), and far easier to drive. You could just hook up the headphone L/R output from an MP3 player to each of the mirror's coils! (not mentioning any evil Ap*le stuff).

    Obviously this will only allow X and Y signals (without music) unless you sync two MP3 players together. To generate the X/Y signals, just use James' excellent LaserBoy software.

    The problem is, LaserBoy assumes that you will of course be using uncompressed Wav files - if you try to compress the Wav to MP3, you will see ALL sorts of graphics glitches from the scanners. This might be OK if you just want simple abstract graphics though?

    Quite a few MP3 players can play Wav files now. They also might resample everything, so you'll need to change the output sample rate in Laserboy for the best graphics quality.

    OzOnE.

  3. #3
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    Feb 2009
    Location
    Bedfordshire
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    46

    Default

    Quote Originally Posted by OzOnE View Post
    Hi,

    I'm probably not the best person to ask about where to buy dichros, but for small galvos you could try finding some older barcode scanners? They used to use small mirrors in them which sat on springs and were scanned with a small coil.

    Not sure about 10mm galvos, but the mirrors could be made even smaller than the sled steppers. I'm assuming that all laser galvos will be MEMS based in the future?

    Those would be better than steppers (for simple graphics), and far easier to drive. You could just hook up the headphone L/R output from an MP3 player to each of the mirror's coils! (not mentioning any evil Ap*le stuff).

    Obviously this will only allow X and Y signals (without music) unless you sync two MP3 players together. To generate the X/Y signals, just use James' excellent LaserBoy software.

    The problem is, LaserBoy assumes that you will of course be using uncompressed Wav files - if you try to compress the Wav to MP3, you will see ALL sorts of graphics glitches from the scanners. This might be OK if you just want simple abstract graphics though?

    Quite a few MP3 players can play Wav files now. They also might resample everything, so you'll need to change the output sample rate in Laserboy for the best graphics quality.

    OzOnE.
    Thanks, I agree about MEMS although I am still only taking baby steps here. There is a huge knowledge gap that I'm trying to fill in a creative way. I'm looking at microcontrollers such as the Arduino to preprogramme a selection of defined patterns rather than just abstract ones. This is a project that covers a lot of ground for me personally but one that I think is worth pursuing. It ties in with my college studies: Electronics; control systems; miniature engineering and my love of coherent light, (both these last ones are simply my interests)!

    There is a, 'system integration', approach to this that presents it's own challenges but that's all part of the fun isn't it?!

    Am I right in thinking barcode scanners are really based on rapidly rotating mirrors? This would be a difficult angle to get the patterns I'm after. The step to bigger and better things is to understand the basic control elements to larger, more conventional and precise galvo controlled systems for displays.

    Any input on this is gratefully received but there are limits to my understanding at present. The willingness to learn is here already though!

    Thanks,

    M

  4. #4
    Join Date
    Dec 2009
    Location
    Devon
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    Default

    Hi,

    I was thinking more of the old hand-held barcode scanners. Most of the more recent ones just use LEDs, and spread a wide beam. The older (or higher quality?) scanners used the small vibrating mirror to scan a puny laser.

    I think using steppers will always give the "stuttery" look to the graphics unless you employ some linear stepping techniques (current ramping). No doubt you've seen the cheaper club lasers which use steppers? They're often pretty rough IMHO.

    The most straightforward way of getting half-decent graphics is by using some coils and mirrors. You might be able to to put a simple hinge / flap on the bottom edge of a mirror, then attach springs to the top edge (on either side, so they cancel each other out and centralize the mirror when the coil is idle).

    Or, you could look into using the voice coils from small 2.5" or 1.8" laptop hard drives. Even easier to glue mirrors directly to the pivot point, but you might need some springs or something to dampen the swing angle.

    Somewhere amongst my "junk mountain", I still have a small amp module from a car stereo hooked up to a hard drive voice coil. I never bothered with adding the Y axis though since buying some proper galvos (cheap, but good LSP-20 equivalents).

    You've actually got me thinking about this now. Although, I've just ordered some AixiZ modules, holders, a 445nm diode and a LPC-815 sled. So, I'll probably have my mind stuck on getting the projector built for a while.

    I'm currently using a cheap C-Media USB sound card and DIY correction amp which works quite well - ideally I'm looking to build a standalone controller though. It would be fantastic to stream ILDA directly from an SD card. This guy has an amazing setup (for home built)...

    http://www.youtube.com/watch?v=MsaYcX5aIac&fmt=18

    I did try to get a DVD Audio disk burnt which would play 6-channel uncompressed PCM on a DVD player, but my cheap players wouldn't play it. My Pioneer should play it, but my sister "borrowed" it.

    The idea is to bypass the DC blocking caps on the DVD player (like you do for the "sound card DAC" mod) and feed the audio into a correction amp. This would give you a nice standalone lasershow player. It could even output the music at the same time if you don't need more than 4 channels for the projector (many DVD players output 5.1). Actually, it might possible to modify the opamps in some DVD players so you won't even need to build a separate correction amp.

    Even better would be to find an MP4 player which can handle multichannel Wav files and also has the required number of audio outputs. (I'm still looking out for something suitable for playing Laserboy Wav's.)

    OzOnE.
    Last edited by OzOnE; 06-07-2010 at 21:31.
    "It's like lasing a stick of Dynamite."...
    http://www.youtube.com/watch?v=0ds0wYpc1eM&fmt=18
    Surely all PL members have seen this movie?

  5. #5
    Join Date
    Feb 2009
    Location
    Bedfordshire
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    Default

    Quote Originally Posted by OzOnE View Post
    Hi,

    I was thinking more of the old hand-held barcode scanners. Most of the more recent ones just use LEDs, and spread a wide beam. The older (or higher quality?) scanners used the small vibrating mirror to scan a puny laser.

    I think using steppers will always give the "stuttery" look to the graphics unless you employ some linear stepping techniques (current ramping). No doubt you've seen the cheaper club lasers which use steppers? They're often pretty rough IMHO.

    OzOnE.

    Yep, stuttery is what I'm after at this point. Remember this is for a pocket sized scanner. No room for HDD coils and the like. A vibrating mirror will not give me control of exactly where my beam is goning to go without a much more complex, closed loop feedback cicuit. No need for this with steppers. Not looking to wow the world at this stage, (except maybe with size), but cheap club laser effects in my palm will suffice.

    M

  6. #6
    Join Date
    Jan 2007
    Location
    Yorkshire, UK
    Posts
    4,572

    Default

    Hi Morgan

    I've got a pair of the 'old' Laserwave dichro's somewhere kicking around. You may recall Rob upgraded them to the newer dichro's at Surfleet. One of them was chipped when removing it, but there's plenty of room left for a beam to get through. They're yours if you want them (provided I can find them in my workshop). They may not be exactly what you want but may get you started.

    Send me a PM with your details if you want me to search them out.

    Cheers

    Jem
    Quote: "There is a theory which states that if ever, for any reason, anyone discovers what exactly the Universe is for and why it is here it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another that states that this has already happened.... Douglas Adams 1952 - 2001

  7. #7
    Join Date
    Jul 2008
    Location
    Maryland
    Posts
    1,635

    Default

    Quote Originally Posted by OzOnE View Post
    Hi,

    I'm probably not the best person to ask about where to buy dichros, but for small galvos you could try finding some older barcode scanners? They used to use small mirrors in them which sat on springs and were scanned with a small coil.

    Not sure about 10mm galvos, but the mirrors could be made even smaller than the sled steppers. I'm assuming that all laser galvos will be MEMS based in the future?

    Those would be better than steppers (for simple graphics), and far easier to drive. You could just hook up the headphone L/R output from an MP3 player to each of the mirror's coils! (not mentioning any evil Ap*le stuff).

    Obviously this will only allow X and Y signals (without music) unless you sync two MP3 players together. To generate the X/Y signals, just use James' excellent LaserBoy software.

    The problem is, LaserBoy assumes that you will of course be using uncompressed Wav files - if you try to compress the Wav to MP3, you will see ALL sorts of graphics glitches from the scanners. This might be OK if you just want simple abstract graphics though?

    Quite a few MP3 players can play Wav files now. They also might resample everything, so you'll need to change the output sample rate in Laserboy for the best graphics quality.

    OzOnE.
    Well using mp3 is a BAD idea.. the compression can make things REAL bad for the galvos... uncompressed wav has all the signals needed but when you compress it you are removing data which is BAD for galvos....

    Now if you really want to get more info regarding the laserboy software check out laserboy.org/forum and ask james anything you want....

    I like laserboy for all kinds of stuff.. Spider Player makes a GREAT player for playing 6 channel waves
    Quis custodiet ipsos custodies?
    Solid State Builders Group

  8. #8
    Join Date
    Dec 2009
    Location
    Devon
    Posts
    48

    Default

    Yep, uncompressed audio is a requirement of Laserboy and any of the "Ez-audio" type DACs.

    Important safety tip - I would never normally recommend anyone to use audio compression on the Wav files unless you've built some VERY cheap / expendable homebrew scanners (and don't mind risking their eventual destruction!)

    MP3 compression discards a ton of info (of course that's the whole point), so it will often destroy a lot of the original graphics info in Laserboy waves. Also, it's likely to introduce random glitches, DC offsets (at correction amp output), and possible rapid "spikes" / voltage swings in the signals which could cause damage to normal galvos / amps.

    I only mentioned compression as a solution for a very crude method of displaying abstract graphics on experimental scanners. Morgan is looking to build something as a proof-of-concept, so I assumed he wouldn't be too bothered about the quality of graphics at this point (or the life of the "scanners").

    The only thing about Laserboy is that the Wav files are quite big to handle if you're not using a PC - I'm looking to build a standalone player which will play ILDA frames directly from SD card (as well as playing the MP3 music simultaneously). This would be a great solution for making the whole show more portable. You could even add a Class-D amp module to your projector for the music!

    Basically, something like Chan's controller board but plays ILDA files directly (instead of his custom format)...

    http://elm-chan.org/works/vlp/report_e.html
    http://elm-chan.org/works/vlp/ldpctl2.jpeg

    OzOnE.
    Last edited by OzOnE; 06-10-2010 at 21:18.
    "It's like lasing a stick of Dynamite."...
    http://www.youtube.com/watch?v=0ds0wYpc1eM&fmt=18
    Surely all PL members have seen this movie?

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