Everything I had read thus far told me that I needed a circuit which supplied a constant current to the laser diode.  It would have been easier if I could have just connected the laser diode to my DC power supply and adjusted the voltage, but that would have been too easy. 

By the way, this is part 2 of a two part series on this project.  If you missed part 1, you can review it here.

I’m not very good at designing my own electronic circuits, so I thought I’d cruise the internet to see if someone had put one together already.  Sure enough, I found a circuit Joey Hagedorn’s web site.  Apparently he tried something similar to this project, but with a different laser pointer.

The circuit I ended up using is shown above.  I ordered all of the parts from Digikey.com, which came to $4.60, which included $2.02 in postage (U.S. Postal Mail).  I love this company, they have what I need and they shipped the parts out fast!

Here is what I purchased for the circuit:

1. One LM317TFS-ND IC Regulator (adjustable)
   

2. One 47 uF capacitor (P802-ND)
   

3. One 10 uF capacitor (P807-ND)
   

4. One 0.1 uF capacitor (P820-ND)
   

5. One 100 Ohm potentiometer (3309W-101-ND)
   

6. One 15 Ohm resistor (CMF15.0HFCT-ND)
   

7. One diode (1N4002GOS-ND)
   

I wired everything up on a breadboard that I had from a previous project, and I even set up the circuit to match the schematic shown above. 

As you can see from the photo, I used a common red LED I had to test the operation of the circuit.  Sure enough, the LED lit up (although it was very dim), and I even had my multimeter connected to measure the current in the circuit.  The LED would draw anywhere from 5-10 mA from my circuit.  I adjusted the potentiometer to somewhere in the middle and increased the voltage from my DC power supply to 8 volts.  No change in the LED brightness, which means my laser diode would be safe at 8 volts DC.

I then tried to find out from Sam’s Laser FAQ site which pins on my laser diode were supposed to be used for each connection.  The site is a good site, but has too much information, and I just wanted to get started.  I made a guess and wrote it down. 

Next, I put on some laser safety goggles that I had previously purchased (for another project) just in case this laser diode was bright enough to damage my eyes.  I also set up my video camera to make sure I could see the beam if it emitted infrared light instead of visible light.  I made a guess for my connections and connected the Blu-Ray diode to my circuit. 

Nothing happened.  Maybe I had a loose wire?  Nope.  I also noticed that my meter wasn’t detecting any current.  I tested the circuit again with the red LED.  Yes, it worked just fine.  I then began the process that any experimenter tries when something doesn’t work right.  I started connecting the positive and negative wires to any of the three leads I could, hoping that I just had my laser diode pins identified incorrect.  After about five different combinations, I found one that emitted blue light.  It worked!

I was a little surprised to see that the blue light being emitted wasn’t focused into a reasonable beam.  I guess I should have expected this, but I was surprised none the less.  The blue color doesn’t photograph well, but you get the picture.  The real color isn’t that much more impressive, so you’re not missing much.

I grabbed the lens assembly I had saved from the Sharp Blu-Ray player and put it in front of the beam.  Neither lens on this assembly focused the beam down like I wanted, so I found another lens I had lying around.  That didn’t work either.  I’m going to have to work a little harder to figure out how to focus this beam down, but at least I have a working blue laser!

At the end, I noticed that my multimeter was measuring 25 mA of current.  I adjusted the potentiometer upwards and the meter went up to 30 mA.  I think this is a safe level for continuous operation, as explained by others who tried this same experiment.  A video of the diode in operation is included below.

Watch for future updates here as I finish the construction and package this circuit into a working blue laser pointer!