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Simple, low-power lasers

Discussion in 'General Electronics' started by Gwyn Morfey, Sep 2, 2003.

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  1. Gwyn Morfey

    Gwyn Morfey Guest

    Hi -

    I'm trying to set up a number of low-power (<=1mW) visible laser
    beams, running continuously for hours at a time. I started with cheap
    ($AU10) laser pointers, which worked fine off batteries, but replacing
    the batteries was a pain. So I hooked up a 4.5V supply to them..

    ...Bzzp. Thank you for playing. Seven dead laser pointers later (and
    some frustrating hours thinking "but I'm sure that's 4.5V.. why is
    that so dim? why wasn't it dim before?"), I'm looking for a better

    From googling and reading old threads here, I gather that I need to
    build a current regulator using the built-in photodiode, for every
    single laser. This looks fairly involved. So how do off-the-shelf
    laser pointers survive without them? Is it something to do with
    limited maximum current from small batteries?

    This URL [ ] seems
    to be selling just the diode, and saying "just hook up a battery and
    you're good to go". How's that work?

    I don't need a lot of brightness (just enough to trigger an LDR), so
    running the diodes at way under their max output would be fine. Is
    there a simple way to keep them shining without eventually killing


  2. Perry Noid

    Perry Noid Guest

    Is your 4.5V power supply AC or DC?

    I ran a similar lazer pointer off a regular 9 volt battery for a long
    time without problems, tho not continiously. I was too lazy to put a
    resistor in line to protect the lazer, sides, i wanted a little more
  3. Gwyn Morfey

    Gwyn Morfey Guest

    Is your 4.5V power supply AC or DC?
    4.5V DC, as supplied by the joystick port on a PC. I gather the port's
    good for several amps, which is probably the problem.
  4. Andre

    Andre Guest

    Nah, they depend on the internal resistance of the button cells in
    series with a 51 ohm resistor. See Sam's Laser FAQ , this is
    documented in much detail.

    The modern (cheap) red LD's are built to be slightly more robust than
    normal , though they still get fried by static just as easily. The
    trick is when you get one, to solder the recommended protection
    circuit across the LD (making sure to work at a static safe

    Also you would want to use some sort of constant current IC (such as
    an LM317LZ) to make sure that the LD survives under most conditions .

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