LG BE12 - red diode laser build

I'm about to start, attempt, to create a pointer using the red diode from a LG burner.

This weekend I dismantled my LG drive and removed all three diodes (BluRay, DVD, CD). I completed a DIY build with the BluRay diode - see this topic for more:
http://laserpointerforums.com/f38/lg-be12-bluray-diode-pinout-88119.html

I'm wondering, before I began this next project, if anyone is familiar with this red diode, pictures below? It's a sealed, rectangular, package.





It looks that with a little sanding and thermal glue this unit will be mated to a Meredith housing. 4AA batteries and DDL (LM317T) protection circuit.

If no one knows this diode I'll assume the far left pin is (-), far right (+)

The center pin is negative. The outer pins are both positive. One will be for the IR diode and the other for
the red one. When it's face up, the red one will be on the right, but it's hard to tell how that one is
mounted. Just don't look into it when you're testing it. The IR output will look like weak red and the red
will be very bright, so it's pretty easy to tell them apart. Test it at 100mA, but be careful, it will get hot very
fast without a heatsink.

In the video below I demonstrate how to determine how much resistance is needed in the LM317 (DDL) circuit for the diode to consume a given amount of current -

This is useful for evaluating any laser diode before continuing a build. This is the red laser diode from the LG BE12. After testing the diode you MUST short the electrolytic capacitor before disconnecting power to the diode!! If you don't do this the diode will probably die. The electrolytic capacitor should be shorted before removing or attaching the diode to the circuit.

Here I've completed soldering up the protection circuit. I'm certainly not very adept at soldering - it's something I only do a few times a year. Although if you've never soldered before you will have to practice before attempting this -



I determined (above video) the amount of resistance to run the diode at 185mA and hope it lives more than a few hours. My experience is few of these diodes live long consuming > 150mA.

Here's the circuit, tested, before continuing with the build



It's going to be very difficult to mate this weird square diode with any lens assembly. I'm still cogitating on how to proceed.

Flogged --
Long ago when these flat diodes came out, I milled a slot in an Aixiz mount
and silver glued it in. It was just OK. They never really caught on here because
of the hassle in mounting and alignment.
HMike

I need more machining tools!

I got the flat pack crudely mounted in the optics housing. It not quite centered nor flat, however will have to do for now. Arctic alumina'd into place. I did sand down the edges of the heat sponge.. ug lead dust. Here are some pictures.





Work continues on the laser brick. Glue and more glue -

Here's a very difficult part of the build. Cutting out parts of the thick plastic project box. In the past I would slowly cut through the plastic using an Xacto knife. This required half a dozen blades and hours of time slowly deepening the cuts. Often the tip of the knife would break off.

This time I used the hot knife method. It's a cruder cut, though much less time required and more satisfying. Heat the stove top to close to red hot and use a blade not too important to you.

Here are the cut-outs for the switch and lens barrel, before sanding.

flogged said:

I need more machining tools!

Click to expand...

Don't we all. LuxIgnis was pushing one up to 500mA, but that was on a good heatsink. O-like
was selling them pressed into a special module.

It's also a good idea to check the current output of a driver using a dummy load (Jufran sells them)
before connecting your precious diode.

The resistance value can also be derived mathematically if you know your desired set current. The
formula is R = Vref / I. Vref for the LM317/338 is 1.25V. So for your example of 200mA, R would come
out to be 1.25 / 0.2 = 6.94444444444. So basically 7Ω. Check out the LM317 datasheet, there is lots
of useful information on there as well as example circuits (mostly for CV, not CC).

To calculate the wattage for the resistor, just use Ohm's law.

W = I * V = 1.25 * 0.2 = 250mW (1/4W), I would go up to at least 1/2W to keep temperatures down and
prevent brown marks on the board.

Also, you're still soldering the boards upside down. Good video, though, it should help out lots of
new members.

Waiting for the glue to dry. YaaaAAwn. Later this evening will finish soldering things up. The switch is from the controller of an IR UFO hoverball. Toy was great fun, Christmas gift, however it was a miracle of planned obsolescence and quickly wore out

I'm worried the diode is not centered well enough for this laser to be a good burner. Will see.

I finished soldering things up, diode still lases.

Now, unfortunately, I cannot get the LD focused. With Meredith housing screwed as close to diode as it would go, with flange sanded down, nowhere near focus. Then I rested the Meredith acrylic optic on top of the LD.. still not focused.

Now I'm thinking one of the two tiny optics in the diode sled may be required, see picture below. Which one - red coating or blue coating?

They really did not want this diode transplanted into a pointer!



edit - Meredith acrylic lens left of sled lenses in picture. I'm thinking of attempting to glue one of two sled optics to the top of the diode, assuming it focuses. Ack. It will not be a focusable laser

Both sled optics easily popped using a jewelers flathead screwdriver. Blue coated, when resting flat side down, directly on top of laser diode (image below), focused the laser.. however focus point no more than an inch or two from the diode!! At greater than half a foot away very out of focus. Sheesh.

So.. to get a more reasonable distance for the beam waist I've got to somehow space the lens.
Hmmm...





Looks like a premium diode. Here's the spot on the ceiling, 1-2 meters from the laser, using sled optic -



Compare the spot to my favorite DIY laser pointer. I modified an LED flashlight. It uses an SDL-7501 laser diode. This is a 90's laser diode. 15mW @ 635nm. Been using the diode for over 10 years, still functions.



Here's the focused spot from the SDL-7501 at 20 feet. I'm holding an American quarter next to it. It's more of a slash than a spot. The LG red appears rounder, though the sled optic may be a diffraction grating. I imagine the fat light cone would be advantageous in a DVD device as it would be less prone to dust on the surface of the disc.



I'm worried more than one lens will be required to narrow the light cone from the LG diode. Sigh. Any suggestions?

A while back, TunedCavity made what he called the "Super Lens" using 2 of the optics from a sled. I don't
know if it will help, but it's something to try. The diode might be recessed too far down inside that
"module."

F*ck. Out of luck. I've got to move the lens closer to the diode to get a focal point > 2 inches. This is not possible as there's a lip around the circumference of the diode aperture.

I haven't given up yet, however am not optimistic. It's a lovely diode, and, designed to be very difficult to modify into a laser pointer

I can think of two approaches, besides sanding down the lip around the diode's aperture - not a good idea.
1) As suggested above, a two, or more, lens gathering - complicated!
2) Attempt to sand/cut down the circumference of the plastic lens (a nearly perfect optic) such that it rests on top of the diode window (not the lip).. and hope this yields a focus point close to infinity.

Success! Two working laser bricks from the LG drive -



I had to sand down the flange on the Meredith housing, and glue the optical assembly together. Instead of using the spring. There was not enough space between the optics and the diode for the spring to fit.



Unfortunately I could not get the diode centered accurately in the housing. Here's the focus at 20 feet, with significant flare.



So it's not the greatest burner, though not a complete failure -


However it's a brilliant pointer, at least 70-80mW I reckon.

Wow, I came across a few of these diodes and just tossed them.
Nice work and good on you for not giving up!