250mW 650nm DVD Laser Build

[loreadarkshade]

This diode was extracted from a 16x DVD burner from an old PC lying around. I used a cheap dollar store pet laser for the adjustable lens. The flashlight host is a cheap $5 aluminum case. I used a simple LM317 driver using the flashlights 3 AAA batteries to get my diode working. I used a 25c coin to make the heatsink lol.
This laser is capable of burning pretty much any black surface. Be safe !

Total cost: $15.45 CAD
Time: 5 painful hours
Parts used: 16x DVD Burner, Cheap laser lens housing, $5 flashlight host from Canadian Tire, LM317 Driver.

Pictures:
Flashlight Host
Build Prep 1
Build Prep 2
Cheap diode housing
Build Parts
Cheap Laser Lens glues to Flashlight End
Quarter Heatsink Lol
Driver Fitted
Result , Beam Shot , Burning Tape

 

[Cyparagon]

3.6V isn't enough for the driver to stay in regulation. Check the voltage across your set-resistor and you'll see it's under 1.25V.

wtf is 650mW in the title?

 

[loreadarkshade]

3.6V isn't enough for the driver to stay in regulation. Check the voltage across your set-resistor and you'll see it's under 1.25V.

wtf is 650mW in the title?

The batteries fully charged give 4.5v. Where did you get the 3.6V from ?

Thank you ! I hadn't caught that, meant to say 650nm haha

Honestly I'm new to this laser / electronics hobby and the LM317 driver confuses me so much. I understand that resistance controls current, but i also noticed the driver caps off to a maximum voltage too.. how and why?

So to make sure my driver is being driven corectly (input voltage sufficiently high), I need to check voltage across resistor and it must be 1.25v.. okay thanks I did not know that!

But, what will be the output voltage? Say I input 12v, or 6v.. that is the confusing part to me.

 

[loreadarkshade]

3.6V isn't enough for the driver to stay in regulation. Check the voltage across your set-resistor and you'll see it's under 1.25V.

wtf is 650mW in the title?

Also, do you know how I could determine the power needs for a unknown diode?

My tools are:
multimeter
bench power supply (doesnt have current control)

 

[FireMyLaser]

The output voltage will be whatever the diode wants, if you have enough input voltage. For a red diode it will be about 3V out. But the LM317 driver and set resistor also drops about 3.5V. So minimum input voltage to maintain regulation is about 6.5V, round up to 7V to be sure. Using excessive input voltage will make more wasted heat in the regualtor. Using less input voltage wont hurt anything, but the laser wont get the full set current. Also it is very important that you keep the metal tab of the regulator electrically isolated from the host.

Knowing the allowed current for an unknown diode is a guessing game. I have collected data from all my diodes and make my own guess by looking at the threshold current and voltage drop at 20mA. Usually 250mA seems to work fine for DVD diodes, if it's from a burner.

 

[loreadarkshade]

The output voltage ...

Thank you so much! That makes SO much sense! So laser diodes are VOLTAGE dependant?? (Using the LM317) That's like opposite of everything I know!! :O

What do you mean by threshold current at 20mA? Could you explain how I can do this myself?

Also, that cracklin oats video in yout sig terrified me! Haha well done.

 

[FireMyLaser]

I mean I use my adjustable power supply to test an unknown diode at 20mA and record the voltage drop. Then I adjust the current until I reach the lasing threshold and record the current and voltage drop again. Then I can make the guess of what kind of diode it is and how much current it may handle. This is just my method and I don't know if anyone else does this.

 

[Cyparagon]

You have a lot to learn about alkaline cells. You'll find the voltage drops substantially under load.