These are instructions on building a very bright, very low power portable light for less than $100. I use these on my bike.
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Step 1: Gather Parts.
64 16000mcd LEDs -- you can use other LEDs if you cant find these.
4-5 dipole molex connectors
1 micromini toggle switch
1 type N or M DC connector. male and female.
a spool of approx. 26 guage wire.
a spool of approx 18 guage two strand wire.
4x2 project box
small (at least 2x3) circuit board, prefer through hole.
two part polyurethane resin
real rubber weather stripping
2 lithium ion batteries and a charger for them
I buy a lot of LEDs from these folks:
I bought my batteries from here:
I bought my resin from TAP Plastics in San Francisco:
http://tapplastics.com/ - Look for the "Quick Cast" two part resin.
Most other parts came from what I had laying around, or from the nearest RadioShack.
These lights take around 4-5 hours to build if you dont do these kinds of things all the time.
Step 2: Getting Started!
Heat up your soldering iron, and get out your LEDs and sidecutter.
I assume you're using LEDs with a 3.3v forward voltage drop. In fact, the entire project uses that assumption. Adjust your numbers accordingly if that's not true for you.
You will solder down 16 rows of 4 LEDs, so stuff the first row in to the board. You'll connect these positive to negative down the row, so make sure they all point the same direction.
Step 3: Flip the Board Over.
Stick your thumb over the LEDs and turn the board over. Bend the leads down so that your LEDs wont fall out when tacking them.
Notice how these are connected, you'll do this another 15 times.
Step 4: Cut Off the Soldered Leads.
Clip the soldered leads flush and bend the outside leads away from the row.
Next, bend your unsoldered leads down to the leads you just cut flush and solder them together.
Connect a 12 volt power source to each row when you're done soldering it. That way you know that each row works before moving on to the next.
Once you have 8 rows soldered down, your project will look similar to the photo for this step.
Step 5: Tie the First 8 Rows Together.
Bend the outside leads upward. Leave the top most leads long.
Cut the rest of the leads off and solder them to each other.
Step 6: Start on the Last 8 Rows.
Insert your next set of LEDs in between the rows which you've just soldered. The leads will be perpendicular to the first 8 rows, and the positive and negative leads will alternate being upward and downward. e.g:
+ - + -
- + - +
The LEDs may be a little hard to get in between your existing rows, but a little press with your thumb should send them in to place.
Experiment a little with this row before soldering, and it'll make sense.
Step 7: Solder Down the Last 8 Rows.
Connect each row to your positive and negative leads from the first 8 rows. You'll have to use a small tool to jump the negative lead for one of your outside LEDs.
Dont worry about insulating the leg you used to jump the negative lead, because you'll be casting this in resin at the end of the project.
Step 8: Attach Leads.
You're done with the hard part. Make sure all your LEDs are lit. Run your thumb over the solder joints for a bit and make sure they dont break. Resolder anything which comes loose.
Insert a couple of approx 26 guage wires through the LED side of the board and bend them over on the solder side. Connect up the long legs you left at the top of the board to them. Test the array again.
Step 9: Trim Down Your Board and Project Enclosure.
Cut your board down to size. I've seen people use a razor knife, a dremel tool, and tin snips for this. Find what works best for you. I prefer a razor knife and then a dremel tool for the final touch up. Knock the corners off the trimmed board.
Trim your project enclosure until you can get your board to easily rest on the shorter set of standoffs. Secure the board with toothpicks.
Step 10: Cast the Project in Resin!
This is a little bit tricky, so improvise as needed.
Block the section of enclosure off where you will place your switches. Dont drill the holes in until you cast the board in the resin.
Mix your resin and fill the enclosure up until the board is just barely submerged. Make sure to do this on a complely level surface. You cant go back once it's hardened, so make sure your light is working properly and that you like your board placement.
Step 11: Remove Cardboard and Toothpicks, and Allow the Resin to Set.
Wait until the resin has hardend just a little bit, and remove the toothpicks and cardboard.
Next, wait until your resin is completely set before moving the light to another surface.
Step 12: Drill Holes for the Switch and Power Connector.
Knock out the two exposed posts, and drill in the holes for the switch and power connector.
Solder them up and fold the wires aside. I like to keep a little length to them so that if I need to replace a switch sometime later, I have some extra wire to work with.
Step 13: Buff the LEDs and Close the Case Up.
Take a dremel tool or a soft cloth and buff off fingerprints of residue from the resin from the LEDs.
Cut a length of rubber weather stripping in half and line the edges of the light with it.
Fashion a cover for the front out of a sheet of 1/16" plastic or whatever else you might want to use. I've heard of people using plastic milk jugs as a diffuser as well.
Take a length of duct tape and tape down the cover to the weather stripping. This allows you easy access to the enclosure if you're on the road and need to work on a switch.
Step 14: Cook Up the Power Source.
I ended up settling on using surplus Lithium Ion batteries for this project. I use two 8 volt cells in parallel.
Apply flux to the battery leads and solder down your wires to the terminals.
A side note:
If you dont want to use these batteries, you can use conventional NiMH batteries. Your local electronics shop will carry holders for them.
While the LEDs are soldered to take around 12 volts at about 33mA, I found that I could drive my LEDs at a brighter output with around 16 volts at 41mA. Mess around with it.
Step 15: Modify the Battery Charger to Use Molex Plugs.
Open up your charger and attach two wires to the leads inside for use with your molex connectors.
Step 16: Make a Y Adaptor
Wire up a "Y" adaptor to connect from two batteries to the cable which plugs in to your new light.
Step 17: Attach Mounting Hardware to the Enclosure.
I pulled off a mounting bracket from an old bike light, and superglued it to the enclosure. You can do what you'd like with yours.
Step 18: Conclusion
You've just built a bike light which is brighter than most car headlights and weighs in under two pounds with batteries.
I'd love to hear from you if you build one of these, and would love feedback on how well it worked for you or any brilliant modifications you made.