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PWM control

Discussion in 'Electronic Design' started by Dave, I can't do that, Jul 30, 2008.

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  1. Hi people,

    I have an 1992 Synrad laser. I need a PWM controller to set the
    intensity. I'd like something that has an input that can be controlled
    by a pin on the Parallel port of a computer, but will be happy with a
    manual control that I can set for intensity.

    Because the laser is so old Synrad no longer has any info on it. I
    have made it burn stuff by using a AA battery on the intensity line so
    II know it is working now.

    I am retired and on a tight budget but thought I may be able to use
    this to engrave stuff and a make a few bucks on the side. It was given
    to me because the laser was dead, but I now have it working albeit at
    only one output level. <grin>

    Synrad did say it was controlled by a PWM signal. From their
    controller manual...
    1us tickle pulse at all times to keep the laser on the verge of
    Output voltage is 0-5vdc.
    Output current 100ma through a 50ohm CMOS driver
    I get the impression that anything above a 2us pulse will drive the
    laser on.

    Can anyone assist me here with a kit or schematic or something,

    Thanks in advance.

  2. Forgot to mention it is a 5kHz signal

  3. Should be pretty easy. How do you want to go about it? Are you used to
    programming uC or soldering chips?

    One easy way might be to use a 555 timer? There are many kits and schematics
    available. You can get individual PWM chips too. Its very simple to
    implement it in a uC. If your willing to spend 30-40 bucks on the Pickit2 I
    can send you some code that will take the input of a pot and output a
    corresponding PWM. (it needs to be the pic24's though)

    The PicKit2 lets you program pic's pretty easily by just writing
    code(download free MPLAB), and burn it. You can even debug them and it can
    act as a logic analyzer(not used that yet). So its a pretty decent
    investment if you plan on messing around with this kinda stuff.
  4. Rich Grise

    Rich Grise Guest

    See page 5: The first circuit is an astable that puts out your 5 KHz;
    you'd want to differentiate its output (output to 1-10 nF cap, other end
    of cap goes thru 10K resistor to ground AND to trigger of the monostable.
    Design the monostable for a pulse width of 1.0 uS to as long as you want.

    Use that to drive the PWM input, with the appropriate driver.

    Good Luck!
  5. On Jul 30, 12:43 pm, "Jon Slaughter" <>

    Hi Jon,

    Thanks for the reply.
    <grin> Let me answer that by saying I am a retired mechanical
    engineer. <gasp> I have built many electronic kits over the years and
    to the best of my memory they have always worked firs time, so I guess
    I am OK with soldering.

    While I am not averse to investment, in this instant it would be
    doubtful if I would ever use the programming stuff again. I would
    prefer to get a kit or schematic with board layouts.

    All of the kits (except Velleman, none in stock that I have found yet)
    that I have found so far are 12vdc and up. Since the laser is a costly
    part of the project and I lucked out on getting it working, I want to
    approach it very carefully and the 5vdc and 100mA max are paramount
    for whatever I use.

  6. Hi Rich,
    Waaaaaaay out of my area of expertise to design something. Thanks.

  7. Rich Grise

    Rich Grise Guest

    Aw, come on, Dave - it's already designed! All you have to do is
    solder the parts together. Of course, you'd need to use the chart
    to get your R and C values, to give you the right pulse width and
    interval, but that's only arithmetic.

    Or, you might be able to swindle someone here into giving you a
    full design and layout, but at 5 KHz it'd be a great beginner-level

    In any case, good luck!

  8. Thanks Rich,
    The Math will be fine, but this also has to be adjustable for varying
    the laser intensity and it is at that point it starts to get complex
    for my abilities in electronics.

  9. Rich Grise

    Rich Grise Guest

    It's sounding like this would be more appropriate on
    sci.electronics.basics ; You're more likely to get some help over there,
    since it's intended more for beginners; somebody might even slap together
    a schematic for you.

    Good Luck!
  10. Jamie

    Jamie Guest

    I've used a dual op-amp set up where one op-amp act's as the triangle
    wave generator and the other the voltage comparator for the pulse width.

    Something there you can look at..

    I suppose the bulb could be replaced with the laser unit for
    the low side :)"
  11. Thanks Rich, I will try there.

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