Create a portable bike light with enough power to see where you're going.

The goals here are:

* Enough light to see the road.
* Battery life of at least two hours.
* Easy to attach and remove.

Step 1: A Note From the Future

I'm already at work on the next version of this bike light, and I thought I would share the details, since you may be more interested in that design.

* Battery -- Makita BL1830. The arrangement of 8 AAs works well enough, but swapping out eight batteries at a time is a nuisance. The Makita weighs about 700g, but mounting a slide connector to the bike would make for easy use.
* Light: Cree XR-E, from the brightest bin. LEDs from Cree and Seoul Semiconductor now outperform the Luxeons, though Cree seems to be the easier to find optics for.
* Connectors. I definitely want to switch from a single connected wire to a detachable cable, using EIAJ connectors, for example.

I'm still pretty happy with the Cateye as a mount, though I'd love to hear from you if you have mounting scheme that works better for you.

Step 2: Choosing Your Components

The first step is to choose your components. In this section I'm going to go into an explanation for each component I chose. The goal here is to allow you to mix and match while avoiding some mistakes I made.

The Chassis
First, I'm building my bike light on an existing light, the Cateye HL-EL200:

http://www.amazon.com/CatEye-Bike-Head-Light-HL-EL200/dp/B00063857G
http://www.mtbr.com/reviews/olderlights/product_89079.shtml
http://www.blueskycycling.com/product1030_9_-CatEye-HL-EL200-Headlight.htm

Pros:
+ It's cheap.

+ It sucks as a bike light, so you won't miss it. Low power and the cover's difficult to put on and remove. Once everything's in place, though, you'll never need to open it.

+ The boat-like shape means it can hold the new light and electronics without much in the way of modification.

+ It uses Cateye's quick-release mount, which means it's easy to take on and off.

Cons:
- It's hard to find because it's an older model of Cateye.

The power
8 AAs. Whatever you choose, it needs to maintain at least 10 volts. If you decide to go with a battery pack solution, you'll need to redesign the circuit. I went with AAs because they're light and NiMH batteries are easy enough to recharge. Even if you're using a battery pack, be sure to read how I create a velcro mount, as you can probably reuse that. Since this is going on the handlebars, I want it to be light.

The Light Source
4 Luxeon 1s. This design was based on this instructable almost exclusively. The circuit is based on that design, though I end up changing a few things.

The Light Color
White. Don't mess around. In many states, white or yellow are the only two colors you're supposed to have on the front of the bike, and blue is reserved for law enforcement, even on bicycles. My state requires at least one white light on the front, and that means you have no chance of retaining your night vision. Even if you're going to spend most of your time off-road, white will serve you well in getting to and from the trail.

Putting It All Together

You're going to need the following:

* 1 Cateye HL-EL200

* 1 heat sink, about 1.5 inches square on the surface and less than 1 inch thick, like this Aavid Thermalloy model 375024B00032G, with tape mounting

* 4 OP-015 15° lenses

* 4 OH-ES1-CL clear optic lens holders

* 4 LXHL-MW1D White Luxeon Star (Luxeon I)

* 1 3021-D-E-1000 "BuckPuck"

* 1 3021-HEP BuckPuck wiring harness

* 2 battery holders holding 4 AA batteries

* 8 AA batteries (preferrably NiMH rechargeable)

* Soldering iron and solder, electrical tape

* 18 or 22 gauge wire

* Climbing rope with the core removed.

* A lighter or stove burner, to finish off the rope ends.

* Epoxy or silicone for waterproofing

* A large package of 2 inch wide velcro, used for mounting the battery

Step 3: Preparing the Light Chassis

Slide the top off the light. Lift the bulb assembly up and cut the wires. I thought it might be possible to use the rear switch in my design, but it's not a simple switch, at least as far as my ohmmeter says. I ended up removing the entire assembly. To do so, grasp the center column with a pair of pliers and pull up and towards the rear. It doesn't take much force, and the whole column including the button should lift out.

Drill three holes. One in the rear, and two on the side. Look at the attached pictures to see where I drilled mine.

When drilling the hole for the potentiometer, use a 17/64" bit (about 7mm). The others holes should be sized for your switch and the cord or connector you're using for power.

Step 4: Preparing the Battery Pack

In this step, you'll make a battery holder and attach it to your bike. Start with two flat-backed 4 AA battery holders. Rough the surfaces with sandpaper, then epoxy them back to back.

Now cut a red lead from one pack and a black lead from the other short. Tape them together temporarily, load the batteries, and check that your voltmeter shows a different of about 10 volts on the other two leads.

Remove the batteries from the pack. Now remove the tape and solder the shortened leads together. Trim the long leads and solder long lengths of wire to them, say about 30cm (12 inches).

Next, take a length of cord and remove the fiber core. Burn an end to neaten it, and apply epoxy to the outside to affix it to your battery pack, running 1/4 to 1/2 way across it.

Step 5: Mounting the Battery Holder to Your Bike

Find the spot on your handlebar's gooseneck where you'll be attaching the battery pack. Your gooseneck should be long enough to hold the battery pack in a way that it can move freely without hitting anything.

Create a "basket" for the battery pack. We'll be using the two types of velcro "loop" and "hook", and in each case, we'll be making our pieces double-sided using the same kind.

First, measure a section of "loop" velcro long almost long enough to wrap around the battery pack snugly. Cut a second section "loop" the same length. Remove the adhesive and tape them back to back.

Now cut two pieces of "hook" velcro, long enough to form a U-shape that supports the bottom of the velcro. Now you have a basket for your battery pack. You should be able to put the battery pack in the basket and take it out with ease.

Next, cut single piece of "loop" velcro, remove the adhesive, and attach it to your gooseneck.

Finally, cut a double-sided piece of "hook" velcro long enough to attach to your gooseneck velcro and wrap around the battery pack. This is the final piece, attaching the battery pack holder to the bike. Once this is in place, you can leave it as-is.

To remove the light from the bike, push on the bottom of the velcro to lift the battery pack up, then remove the pack and unlatch the light.

Step 6: Wiring It Up

Now that you've tested the battery pack for fit and length, you can start to wire it.

You can wire the bulbs as seen in the image. Make sure the lights are in the same orientation and spaced far enough apart so that the lens holders will fit. Test the battery by connecting it to the output of the wiring harness on the BuckPuck.

Refer to this instructable if you're concerned about how to wire this. Be sure to test the wiring briefly before attaching the bulbs to the heatsink, and then again before gluing the heatsink to the mount.

Look at the "throw" of the bulbs when your lenses are in place, and if you're happy with it, you can affix the lenses with silicone. You can also finish the exposed contacts with silicone if you're trying for a rain-resistant or rain-proofed light. Wait for the silicone to cure.

Turn the heatsink so that one corner is nearly centered on the bottom front of the light holder. Run the power leads through an existing hole into the rear part of the light holder. Once you're comfortable with the position, use silicone glue to affix it. Test that you can still close the top cover, and then leave the silicone to cure.

Now finish soldering the unit together, being careful to use electrical tape on exposed leads.

Step 7: Finishing Touches

Now that everything's in place, you have a working bike light!

There's a small chance that the top of the light can come off, but you can fix that with more velcro.

That's it! Hope you enjoy it.