# Simple, low-power lasers

G

#### Gwyn Morfey

Jan 1, 1970
0
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
($AU10) laser pointers, which worked fine off batteries, but replacing the batteries was a pain. So I hooked up a 4.5V supply to them.. ...Bzzp. Thank you for playing. Seven dead laser pointers later (and some frustrating hours thinking "but I'm sure that's 4.5V.. why is that so dim? why wasn't it dim before?"), I'm looking for a better solution. From googling and reading old threads here, I gather that I need to build a current regulator using the built-in photodiode, for every single laser. This looks fairly involved. So how do off-the-shelf laser pointers survive without them? Is it something to do with limited maximum current from small batteries? This URL [ http://www1.jaycar.com.au/productView.asp?ID=ST3115 ] seems to be selling just the diode, and saying "just hook up a battery and you're good to go". How's that work? I don't need a lot of brightness (just enough to trigger an LDR), so running the diodes at way under their max output would be fine. Is there a simple way to keep them shining without eventually killing them? Thanks, Gwyn. P #### Perry Noid Jan 1, 1970 0 Gwyn Morfey said: Hi - I'm trying to set up a number of low-power (<=1mW) visible laser beams, running continuously for hours at a time. I started with cheap ($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?")

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
intensity.

G

#### Gwyn Morfey

Jan 1, 1970
0
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.

A

#### Andre

Jan 1, 1970
0
Agh! I just ran a new laser pointer for a couple of hours continuously
off batteries with no modifications at all, and after replacing the
batteries, it's definitely dimmer than an unused new one. Looks like
they're built to self-destruct..

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
workstation).

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 .

-A

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