Page 3 of 41 FirstFirst 123456713 ... LastLast
Results 21 to 30 of 405

Thread: The big TEC driver thread!

  1. #21
    mixedgas's Avatar
    mixedgas is offline 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
    9,890

    Default

    [QUOTE=tocket;78522]That's a brilliant idea! Makes it possible to control the TEC with just a microcontroller and H-bridge; no need for a thermistor.


    Dr L, just pmed me with the other problem. Switching noise! Draht! foild again....

    Steve

  2. #22
    Join Date
    Oct 2006
    Location
    Cleveland, Ohio
    Posts
    2,342

    Default

    Quote Originally Posted by The_Doctor View Post
    That's an awesome idea too. Given that closed loop control can allow enough energy to accelerate a mass better than with open loop, it can help with some kind of widget to provide analog mod to a fixed output laser. Probably not fast enough to be useful though, but if it is, it's surely been done in the past. I might try this with a red diode though if it can make a better fade than current-sense control.
    You can't get a much better linear fade with direct injection than current sense control, assuming the diode threshold is set right. What I see optical feedback is useful for is compensating the changes and nonlinearities in conversion efficiency in DPSS lasers at the different modulation levels.

  3. #23
    mixedgas's Avatar
    mixedgas is offline 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
    9,890

    Default

    go over to avrusb and add the usb. With a small atmega, that gives you 6 analog in.

    Steve

  4. #24
    mixedgas's Avatar
    mixedgas is offline 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
    9,890

    Default

    What I wanted to see gone is some of the lag from the 800 microsecond ND upper lasing state storage time.

    Steve

  5. #25
    Join Date
    May 2008
    Location
    nerdtown, USA
    Posts
    1,165

    Default

    Quote Originally Posted by drlava View Post
    You can't get a much better linear fade with direct injection than current sense control, assuming the diode threshold is set right. What I see optical feedback is useful for is compensating the changes and nonlinearities in conversion efficiency in DPSS lasers at the different modulation levels.
    Right, exactly- by closing the loop, you can get a much smoother result.

    My current design uses two of the analogue inputs on an AVR- one to take the modulation signal from the controller card and one to take the output from the photodiode. The photodiode's linearity isn't perfect but it's well characterized and the software in the AVR executes a self-calibration when it starts. At this point the 15-second time delay I have on my projector still hasn't opened the shutter so the few milliseconds (it's not timed accurately, since it doesn't matter) pulses it uses to determine what the minimum and maximum points of the output curve equate to on the diode reading aren't a problem. It doesn't need to communicate with the PC at all during this process but I have it spitting the numbers out on the serial port for testing purposes.

    I haven't got it all nailed down yet (for example, spill light from the other lasers in my rather small optics box interferes with it) but I'll let you know when I do

  6. #26
    Join Date
    May 2008
    Location
    nerdtown, USA
    Posts
    1,165

    Default

    woops, that was "quote", not "edit".

    Quote Originally Posted by mixedgas View Post
    What I wanted to see gone is some of the lag from the 800 microsecond ND upper lasing state storage time.

    Steve
    What I wanted to see gone was some of the crappiness from my Cheap-Ass Chinese Green. :-/
    Last edited by heroic; 01-14-2009 at 18:49.

  7. #27
    Join Date
    Feb 2005
    Posts
    1,131

    Default

    I would like to see versions of big 300+ watts TEC cooling for water chilling,
    the heat exchanger,TEC array,power supply.

  8. #28
    Join Date
    Mar 2006
    Posts
    2,478

    Default

    Quote Originally Posted by Lasernerd View Post
    I would like to see versions of big 300+ watts TEC cooling for water chilling,
    the heat exchanger,TEC array,power supply.
    Horribly inefficient though. For that amount of cooling it's probably better to use refrigerant, and a fraction of the energy input.


    Re that red diode and optical feedback idea, I wasn't convinced it was a goer, hence the 'if'.. but, what if it mode hops like Rohm's do at levels over 150 mW. That hopping changes power out by around 20%, so might it help with that if you want to push for 200 mW?

  9. #29
    Join Date
    May 2008
    Location
    nerdtown, USA
    Posts
    1,165

    Default

    Quote Originally Posted by The_Doctor View Post
    Re that red diode and optical feedback idea, I wasn't convinced it was a goer, hence the 'if'.. but, what if it mode hops like Rohm's do at levels over 150 mW. That hopping changes power out by around 20%, so might it help with that if you want to push for 200 mW?
    Well, I'm not convinced that the reds really need it, but it turns out when I thought a little more, the advantages are pretty substantial:

    - automatic setting of gain curve, max and min points
    - tunable delay on a per-channel basis (so the slow DPSSes come on at the same time as the fast red, reducing the mismatch)
    - linearization on the same scale as the other colours

    This could be (assuming it freaking works... right now it's just sort of sitting there sulking) just the thing to get my RGB to make real greys! It turns out that EyeMagic have already built a similar, but much more expensive and sophisticated thing:

    http://www.eyemagic.gr/laser-iris-colorsafe.html

    I was instantly convinced by their nice smooth greyscales.

  10. #30
    Join Date
    Dec 2007
    Location
    Stockholm, Sweden
    Posts
    551

    Default

    Nice to see some action here!
    Maybe the optical feedback project should get its own thread?

    Does anyone have good sources for small TEC's they want to share?
    The ones on ebay are usually big ones, 40x40 mm or so.

Posting Permissions

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