Resurrected DX20

Nothing too earth-shattering here, but I thought I'd share my experiences with giving a second life to a DX20 pen laser that had gotten to where it wouldn't turn on at all.

This was a 2xAA pen laser, that at the time was $17. Seemed not bad for 20mW, and I got some fun out of it, but it was flaky from the start.
I can no longer find the SKU of this laser, but it looks identical to this one:
http://www.dealextreme.com/details.dx/sku.1619

I've since ordered a DX Romisen 30mW that looks like it'll be much more reliable, so I had nothing to lose in tearing this one up.
Despite all the posts saying that with a vise and a lot of wiggling you could pull the module out, this one wouldn't budge. I took the end-cap, screwed it onto the module, then put the cap in a vise, and twisted and pulled on the back end with pliers - didn't move at all.
I fnally figured what-the-heck, and took a dremel cutting wheel to it. Once I got enough of the barrel cut away, the module came out - wasn't glued or anything, just amazingly tight.

There was no infamous contact-spring in this model, and the switch was not the problem. It turned out to be a bad solder joint on the back of the driver board. Once I re-heated these joints, it started working like a champ.

Then there was that adjustment pot staring at me...
Very touchy - Just a few degrees of turning brought it up from 20mW output to 65mW. I didn't want to go any further than that, and I've since backed off to about 45mW. (The original current from the battery was about 245mA. 315mA gives about 36mW and 457mA gives about 65mW. But it's hard to get good numbers because the output tends to increase as I leave it on.) I don't know what the max would be on this module. In this case though, with no extra heatsink, I don't want to go all that high.

I glued the module into a small project box I had lying around. Added a positive-click MicroSwitch, and (until my rechargeable arrives,) soldered in a CR123 battery.

Here's the result:

Oh yeah, another thing I discovered...
It turns out the (plastic) lens is focusable - kind of.
Behind the front cap, on the front of the module, the lens had been protruding slightly. After I got everything finished though, I noticed that the beam diameter was way bigger than it used to be. Turns out the vibration from the Dremel tool had vibrated the lens and screwed it several turns down into the module.
I ended up taking the point of an Xacto knife to the outer edge of the lens, and unscrewing it back out to where it had been.
I suppose potentially this could be done further to focus down to a better burning dot if that's your goal.

Zarniwoop said:

...soldered in a CR123 battery...

Click to expand...

nice project, i like how compact your whole setup turned out!
since the pumpdiode survived 457mA, you can drive it constantly that high if you use a heatsink and/or fan, i guess. if it was too much for the diode, it would have instantly died.. well, sure, you may reduce its live by some years, but pointers arent used that often anyway, not?

please, please, dont solder directly onto batteries. never. there is no battery which would not get damaged by this high temperature.
with lithium-batteries its much worse: remember them exploding when shorted out? that comes because the dead-short raises its internal temperature untill a thermal-runaway-condition happens. now if you heat it externally, it cant be good, can it? ..and i know, uh, somehow, that it takes long and brutal heat to solder batteries.. ;-)

manuel