DIY Maker Blog by Matt Morawiec
May 22 2014

Laser + USB Charger

A 2-in-1 flashlight host conversion


When I originally saw this host I knew I had to put a laser in it. The convenience of a USB charger built in was hard to resist. The ultimate goal was to have a functioning high power laser with a USB 5v output to charge other devices, and also to charge the laser itself without having to take its batteries out.

Get the Parts

  • Host: "Jinheng 12a 2 in 1" Flashlight from Fasttech
  • Heatsink: As with the Cree 8 and my other laser projects, custom machined by MrCrouse @ Laser Pointer Formus
  • Diode Assembly: M140 Diode with G2 Lens ($90) from DTR
  • Driver Circuit (X-boost Mini): "X-boost" sold by]( ) (sourced from Laser Pointer Forums]( ))
  • Batteries Quality 18650 Li-ion (I use Panasonic NCR18650B cells)
  • SAFETY GLASSES: Visit Survival Laser for safety glasses. Eagle Pairs are recommended
  • Misc: Wire, Hot Glue, Solder, Soldering iron, wire strippers, pliers, hex wrenches, helping hands, thermal adhesive..


The Host

First we need to clear out the original Jinheng flashlight host to make way for all of the laser parts we will be installing. The reflector and LED had to removed to make room for a large heatsink we will be installing to wick heat away from the laser diode. The pre-existing circuit was repurposed to act as a contact pad for the positive and case contacts...

Original host Original Pill/Driver Original LED

Now that the host is completely empty, we can start the build.

The Driver Circuit

The original circuit can be used to route power from the batteries to our new driver circuit. For this, I soldered a black (GND) wire to the outermost ring of the PCB, making case contact, and I soldered a red wire to the spring on the bottom of the PCB through a hole (as this host has positive going to the spring and has a case GND). The rest of the components on the PCB can be left on or scrapped, but you should check for continuity if you decide to keep them on. There should never be any electrical connection between the positive voltage and the ground.

Then, for the new driver, I set an x-boost I had lying around to the highest it would let me: 1.45A. I would suggest driving this diode at 1.8A for maximum performance, but I was unable to achieve this number.

Then I soldered on leads to both sides of the driver and connected everything up (the contact pad to the driver to the diode). We will heatsink the driver directly to the main heatsink later...

But first, I did a sketchy test to make sure we had light!

Quick Test

The X-Boost

Head Assembly

Now I had to unite the -Laser diode -driver -heatsink -contact pad -upper portion of the host

Heatsink by MrCrouse Beautiful!

First I had to secure the driver to the main heatsink. This is the best case scenario for these build as then you do not have to worry about two separate sinks for duty cycle. After installing the pill into the host and setting the 12mm module in the heatsink with a set screw, I used a glob of Arctic Alumina thermal adhesive and taped the driver in place while it dried. Make sure there is enough room in between the heatsink and the bottom of the head so that this driver can even fit.

Waiting for it to Dry

Final Head Assembly

After the paste had dried, I added some extra insulation to be safe.

Extra Insullation

Now all that was left was to put the head together into a completed part. I just slid the heatsink into the host slowly, taking care not to impact the driver, and then I screwed the crown onto the flashlight, making sure the heatsink did not turn with the crown.

Laser Portion

Putting it All Together

All that was left to do was to screw the head onto the lower portion of the light.

Done! Functioning USB Charger

After this you should be done! Put in 1 - 3 18650 li-ions and press the orange tail switch. If the beam is not small like a dot it needs to be focused. Simply turn the lens on the front (dont burn yourself) to focus the laser beam to a dot (really a rectangle).

To burn things you can screw the lens all the way in, then focus to a dot, and then turn it a little farther to create a focus point about 6" to 14" away from the aperture. This is a point where the beam is extremely concentrated and even paper can be set on fire at this point.

NOTE ABOUT DUTY CYCLE: When using any high powered laser devices a duty cycle must be observed, as an M140 diode emits a large amount of heat as waste energy. If this is not taken into account the diode can overheat and die. For a host this size I recommend a maximum of 3 minutes on and 2 minutes off. If at any time the head of the laser is warm/hot to the touch turn off the device immediately.


Got Laser! Across the Room 2 in 1