# constant current laser driver

Over the weekend, I ripped apart an old DVD burner and harvested the laser diode. I needed something to drive it, and there is a simple trick to use an LM317 adjustable voltage regulator as a constant current source.

The datasheet mentions this:

The device OUTPUT pin will source current necessary to make OUTPUT pin 1.25 V greater than ADJUST terminal to provide output regulation.

I used this functionality to build a constant current driver. I tested it with a string of LEDs to make sure it was regulating the current properly. I started with 1 LED and set the current to ~10mA.

I connected the second LED and the current stayed the same.

Then the third.

So. the constant current source is working. Now to test the laser diode.

It works!

I need to find a housing that will let me focus the beam.

I’m not sure of the specs for this laser diode, so I went easy on adjusting the current limit, but theoretically, it should be powerful enough to light a match or burn flash paper.

If you try to do this, don’t forget your laser glasses. You don’t want to lose your vision from something this dumb.