Thanks to dan for his great instructables!
Where this instructable differs is that my four Cree xr-e LEDs are powered by a USB power supply. Any standard USB power supply will work with appropriate cables. My two main power supplies are a custom D cell holder and a Ryobi rechargeable power cell. I also have a plug in wall wart that will power the flashlight and a 12v outlet to USB adaptor that can be used to power it!
While using the D cell housing, the xr-e LEDs will put out a total of 840 lumens at 6v one amp! Standard USB delivers less power at 5v and half an amp but the LEDs still output a very respectable amount of light, maybe around 700 lumens. Unlike most flashlights this one does not produce a beam of light. It illuminates a 180 area in front of it! It's like having a 50 watt incandescent light at your side.
Building the flashlight cost approximately $40 us. Comparable flashlights on the market are probably smaller but cost in the range of $140. It would have cost me slightly more if I didn't have the electronics sitting around my basement from disassembled TVs and stereos.
This took me a while of mucking around with parts so I don't have pictures of the build. I can only explain what I did. Maybe if I build another I'll be able to take more pictures.
Update: We just got back from a camping trip and we brought the Mega Flashlight! We had a few days where we were trying to get the camp cleaned up for bed so animals wouldn't come around. Walking around with a directional flashlight makes it hard to see everything. I stood on the picnic table and was able to illuminate the entire campsite at once! Even though I wasn't helping clean directly, everything went much faster. Now even more I want to figure out how to hang the flashlight say from a tree or some other object.
Please remember to vote for this instructable for the contest!
Step 1: The USB Plug
Step 2: The D Cell Housing
On the other end of the holder, I inserted a rubber stopper. The rubber stopper also has a bolt in it that contacts the positive terminal of the battery. I then soldered a wire to the bolt. I ran a wire through an edge of the rubber stopper to touch the negative pipe.
I then soldered the two terminals to the male USB.
To secure the USB end I squirted in some Gorilla Glue and let it dry then for more strength, I blobbed in some silicone caulk.
Step 3: The Power Cell
Step 4: The Flashlight
As said before, four Cree XR-e LEDs provide the illumination. They are attached to a heat sink that I pulled off a circuit board and ground down to fit inside the PVC housing. The FET came out of a stereo circuit board and the other transistor came out of a TV. I hunted down a few resisters with the appropriate values with my multi-tester and used those. I used a breadboard to build the circuit and test it using a 6v 1a wall wart that I had laying around and then later with the 4 Ds held in my hands with jumper wires on the terminals.
I did have to buy the switch. I didn't have anything but a bunch of really ugly toggles and momentary button switches.
If you want to do something similar you'll have to see dan's constant current LED driver circuit instructable.
Step 5: Future Upgrades
I don't know how practical or useful a head mount would be since it is an area illuminator and not just a point illuminator.
I need to find a really long male USB to male USB cord for stationary power.
A way to hang the light would be really useful, maybe something with a clamp to grip onto objects.
A magnetic attachment would also be a good idea, maybe just integrate it with the clamp?