Introduction: High Power 3-LED Bicycle Light
EBC also operates BikeWorks, a fully-equipped, volunteer-run community bike workshop, where volunteer mechanics teach & help members of the public to learn how to fix their bicycles. EBC also sells used bikes.
This is the introductory video to building a high-power three LED bicycle light. The design here has 3 modes: High, Medium, and Strobe (blinking), and runs on a voltage between 5-10V. The price of the light, including batteries, charger, and worldwide shipping, is about $50 US. Including batteries, it weighs about 200 grams, and should last about 1.5 hours on high mode (and significantly longer on medium or strobe modes).
This light is something that you can build with minimal investment in components and small hand tools. You don't need to know electronics: there are just 18 solder points, 6 drill holes, a bunch of hot glue, and a few screws. It doesn't require a microcontroller. You don't need to know what an Arduino is. It doesn't require you to fabricate metal, use PVC tubing, laser cut anything, or weld. With a bit of experience (e.g. if, for whatever reason, you make a half-dozen), you can put one of these lights together in less than an hour.
The Edmonton Bicycle Commuters' Society occasionally runs in-person courses on designing and building your own custom bike lights: this design or one customized to suit your needs.
This light is the same brightness, about 600 lumens, as the "Three P4" design here: http://edmontonbikes.ca/downloads/bikelights09/ , but the design in this video is cheaper and easier to build and use, and has a cleaner design.
This light works in thunderstorms, blizzards, and has been used in temperatures below -30C.
That power source can be two lithium-ion rechargeable batteries, or four to six alkaline 1.5V cells in series, or five to seven rechargeable NiMH or NiCad 1.2V cells in series (any of AAA, AA, C, or D shapes). A 6V generator would also work, provided it can provide about 9-12W of power (this is a bit high for the average bike generator).
The parts you will need are:
=== POWER SOURCE ($20.11 US) ===
=== LIGHT ($29.20 US) ===
=== TOOLS (if you don't already have them or can't think of a way to fake it) ===
=== OPTIONAL TOOLS (you don't really need them, but they're handy) ===
All DX parts can be purchased from http://www.dx.com/ . Prices there include worldwide shipping. You may be able to source equivalent (or better) parts for less money, or make substitutions, but I've provided the DX numbers to make things easy for those that just want to follow a detailed shopping list and know that all the parts will work together. When ordering the part numbers listed above, you'll end up with extra components, since some of them come in multiples.
Be warned: I have waited up to 4 months for parts to arrive from DealExtreme. I've always received my items, or received my money back if they couldn't ship it or shipped a wrong/defective item. But some times it's a long, frustrating process. They don't make you jump through hoops, but they can be extremely slow to respond.
They're pretty much a lousy retailer and unacceptable by any normal standards, but if you want to save a few pennies and not leave your house, and you can afford to wait potentially forever, they might barely satisfy your needs. If you work at it, you can often find the same (or better) items on eBay for less money.
Step 1: Build the Battery Box
(Apologies for the focus. Still learning how to use my camera.)
Step 1: Clip away the four plastic protrusions/tabs at each end of the box (where the battery terminals will sit).
Step 2: Drill a small hole above each point where you clipped away the plastic. Drill as high as possible so that your battery-holder terminals will be near the centre of the battery terminals.
Step 3: Ensure that your screws and springs are conductive using a connectivity tester. If your multimeter doesn't have an explicit connectivity tester, you can measure resistance instead. A resistance of 0 Ohms (or under ~4 Ohms) is the same thing as a connection, which is the same thing as a closed-circuit (which is the same thing as a short circuit). This is what you want between the head of your screw and its tip.
Step 4: Drive one screw into a hole from the inside of the battery box. Drive the second screw into the opposite corner.
Step 5: Use pliers to pull open one end of the spring and feed it into one of the remaining holes, from the inside of the battery box. Turn it through about a turn and a half. Do the same with the other spring.
Step 6: Check to see if your batteries fit your battery box. If not, make appropriate adjustments of the springs and screws. Make sure you didn’t skip Step 1.
Step 7: Remove the batteries. You must not try to solder with the batteries still in the case.
Step 8: File the tips of the screws down so that you don’t stab yourself. This is an optional but recommended step.
Step 9: Strip a short piece of wire: strip about 1 inch from one side, and 1 cm from the other. Wrap the long stripped section at least one full turn around one screw, so that it wraps back on itself. Twist the other end of the wire around the nearby spring. Solder both in place. Make sure that the solder connects your wire loop on the screw. Test that the screw is electrically connected to the spring, using your multimeter. Touch the probes to the screw and the spring (not to your solder or the wire--you don’t want to bypass your solder points).
Step 10: Cut two wires, about 6-10 inches in length (speaker wire works well here because it comes paired already). If your wires are differentiated, select which colour will be your positive wire and which will be your negative. Strip one end of the “positive” wire about one inch. Wrap it around the screw and solder it. Strip a short length of the “negative” wire and wrap it around the spring. Solder it too.
Step 11: Strip short lengths of the other ends of the wires. Test the connectivity of these to the screw, spring, and each other (they shouldn’t be shorted to each other).
Step 12: Write polarity signs on the inside of your battery box. Screws are +ve terminals, springs are -ve terminals.
Step 2: Electronics Background Knowledge
This video provides some simplified electronics background. You don’t need to watch it to build this light, but it might be a little illuminating if you don’t have existing electronics knowledge.
Step 3: Attach the Battery Box Connector
Step 1: Strip a short length from each of the wires from a female connector. (NB: in this video, I used the male connector. Only do this if you’re confident that the power-supply/battery connector isn’t going to be accidentally short-circuited.)
Step 2: Hot glue around the head of the connector, including both the connector head and the wires. This adds strain relief so the wires don’t pull out of the connector head, if yanked.
Step 3: Slide a length of heat shrink over the two connector wires. Don’t cover up the stripped leads at the end. Apply more hot glue near the connector head, over the heat shrink. Heat and shrink the heat shrink. This holds the two wires together (so they won’t get tangled/caught as easily), adds some strength, and makes it look better. If you want to make it even less noticeable, use a black permanent marker to colour the remaining visible section of the red wire, and to blacken the connector head.
Step 4: Cut two short sections of heat shrink, and place them on the wire coming from your battery pack.
Step 5: Twist the stripped section of the red wire of the connector to the positive wire of your battery box (this is the wire that leads to the screw). Twist the black wire to the negative wire of the battery box. Solder.
Step 6: Slide the heat shrink over your solder joins, and fill the heat shrink with hot glue.
Step 7: Plug in your matching connector and check connectivity. The black wire should be connected to the spring, and the red wire connected to the screw, and the black and red wires should not be electrically connected.
Step 8: Close the battery box and cover the external portions of the screws, springs, and wires with hot glue.
Step 9: When the glue has completely dried (don’t be impatient), open the battery box. If it is glued shut, carefully cut away the glue that’s adhering to the box lid.
Step 4: Attach the LEDs to the Light-housing Circuit Board
Note: At 1:13, I say “conduct the light away from the body”. I meant “conduct the heat away”.
Step 1: Determine the positive and negative terminals of the LED. Check the datasheet of the LED ( http://www.seoulsemicon.com/en/product/prd/zpowerLEDp4.asp - part number W42180). In the LEDs I have, a negative sign is inscribed along the top lip of the black plastic edge of the LED, and the negative side also has a split-metal protrusion (this is the cathode, or negative terminal mark).
Step 2: Spread a very thin layer of thermal paste on the slug (metal base) of the LED. Don’t get paste on the legs of the LED or the clear dome.
Step 3: Place the LED onto the printed circuit board (PCB) of the light housing, matching the positive leg to the first positive-labelled terminal of the PCB (the + sign nearest the large cutout on the PCB).
Step 4: Repeat for the remaining two LEDs. The positive leg of successive LEDs should connect to the negative leg of the preceeding LED. This is how we connect them in series.
Step 5: Check to see that the lens fits over your LEDs.
Step 6: Solder the legs of the LEDs to the PCB, being careful not to overheat the LEDs. Make sure the LEDs are seated flat against the PCB and that the solder flows onto the PCB pads as well as the LED legs. Otherwise you’ll have a poor connection (potentially wasting power and causing flickering or failure).
Step 7: Make sure the lens still fits. If not, you’ll have to desolder the misaligned LEDs to adjust their positions.
Step 8: Apply a very thin layer of thermal paste to the back of the PCB. Place the PCB in the light housing, lining up the three small screw holes and the large wire hole.
Step 9: Screw the PCB down using the smallest of the screws that came with the light housing.
Step 5: Trim the Driver, Then Solder It to a Power Connector and the LEDs
Step 1: Drill two holes in the back of the white part of the housing.
Step 2: File the sides of the larger (bottom) PCB of the driver until it fits (snugly) inside your housing. File parallel to the 3-pin header, and square the diametric side as well. Be sure not to file away the solder contacts of the tiny resistor on the top of the larger PCB, and avoid filing away the outer copper ring of the PCB.
Step 3: Hot glue the connector head of your remaining connector, and slip on a short length of heat shrink over the wires. Leave enough wire uncovered to feed through the back of the light housing, reaching out the top.
Step 4: Solder the black connector wire to the outer ring of the bottom of the driver PCB, near one to the flat sides. Solder the red connector wire to the inner copper circle on the bottom of the PCB, near one of the flat sides as well. If you solder your wires into the middle of the PCB, you won’t be able to fit your driver into the housing anymore.
Step 5: Feed the small leads (that came pre-attached) of the driver up through the back of the aluminum LED base. Solder the red wire to the positive terminal of the first LED (the terminal that isn’t directly connected to any other LEDs), and solder the black wire to the negative terminal of the third LED (also isn’t connected to anything else). Be careful not to touch the dome of the LEDs with your soldering iron, and avoid overheating the LEDs.
Step 6: Assemble and Test the Light
Step 1: Screw the lens on using the countersunk (bevelled) screws.
Step 2: Push the driver into the white section of the housing. Be careful not to pull on any wires.
Step 3: Screw the white section of the housing to the aluminum fins using the long screws.
Step 4: Test your light by plugging it into your battery.
Step 7: Connect the On/off/mode Switch
Step 1: Cut the positive (red) wire coming out the back of light housing.
Step 2: Strip a very short length off both ends of the red wire.
Step 3: Solder one end of the red wire to one end of the switch.
Step 4: Solder the other end of the red wire to the other side of the switch. You may have to add an extra section of wire to reach.
Step 5: Use hot glue to glue the switch to the top of the light housing. Cover up the terminals of the switch (covering the wire and exposed metal) to add strength and protect from short circuiting and moisture.
Step 6: Apply a small amount of hot glue along the bottom edge of the silicone button cap. Place it over the switch, being careful not to get glue on the moving portion of the switch. Continue applying hot glue over the top lip of the button cap, sealing it to the switch.
Step 7: Glue the back of the white part of the light housing to seal off the holes and provide strain relief for the wires that emerge from the back.
Step 8: Place a small strip of foil duct tape over the top of the aluminum housing fins to prevent your light from back-shining.
Step 9: Test. Have fun! Half-press-and-release the switch to change modes.
Note that on high-mode, the protection circuitry of these batteries will trigger (and cut off power) if they aren’t completely charged, due to the high current draw (the protection circuit assumes this must be a short circuit). You can run a second pair of batteries in parallel to avoid this problem--the current draw from each battery will be halved. You can also just switch to medium mode as soon as you turn on the light; you’ll get much longer run-time, be just as visible, and, most likely, still be able to see just as much, because medium-mode is still really really bright.
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