How to Build a Bicycle Light

Remove both ends from a can of tomato paste with a smooth-edge can opener. Clean out the can, remove the label and drill a hole in one of the end capsn. Make sure that the diameter of the drill bit used is smaller than the spring but big enough for the speaker wire to fit. Throw away the other end cap.

Attach the pressure switch to the handle bar of the bicycle using a zip-tie. Position the switch on the area where fingers rest and not where the cyclist will support their weight. Do not position the switch in the way of other controls. Be careful not to attach the zip-tie over the pressure-sensitive portion of the switch or the batteries will drain and the light won't turn off.

Use a cyanoacrylate glue to glue the watch crystal over the front of the halogen bulb. Plastic will not work since it will melt. Other glues may be used (like high temperature JB weld) but need to be able to withstand intense heat. Using a wire cutter, cut the hooked ends off the spring and use a file to take any sharp points off the ends. Solder the spring to one of the terminals of the halogen bulb and make sure that it will hold tightly when it cools.

Strip a wire of the pressure switch. Run the wire through the hole in the lid and into the spring until it is 15 millimeters from where the spring is soldered. Bend the spring to the side by gently gripping it above the solder area with needle-nosed pliers as the spring is bent. Slip the wire out through the newly opened side of the spring. Do not let bare wire touch the spring. Solder the tip of the wire to the other lead of the halogen bulb. Put the halogen bulb into one end of the can. Gently pull the spring out the other end of the can and extend it a quarter inch past the end of the can. Screw the end cap onto the spring so that the spring is threaded through the hole. Keep screwing until the lid is on tightly.

Slide out the wire through the side of the spring. Solder a lead from the wire onto the lead of the halogen bulb that does not have the spring soldered to it. Put the halogen bulb into one end of the can. Gently pull the spring out the other end of the can. Screw the end cap so that the spring is threaded through it.

Tighten the lid onto the cylinder of the can by continuing to screw the lid onto the spring. The other lead from the wire should be soldered to a black wire from a 9-volt battery terminal connector (cut off the red wire). A second terminal connector should have the wires stripped at the base be the terminal and then be soldered together before the rest of the wire that dangles past the soldering is cut away. A third terminal connector should have the red wire soldered to the same lead on the halogen bulb as the spring. Cut off the black wire from the third terminal connector.

Hook up the two 9-volt batteries by taking the second terminal connector (with no wires attached) and click it on to both batteries. Hook up the red-wired terminal connector to one of the terminals on the battery. Do the same with the other battery. If the pressure switch fails to engage, switch the batteries to different terminal connectors, which should remedy the problem of hooking up to the wrong terminal. Place the batteries inside the can.

Slide two zip ties over the handle bars of the bicycle and cross them. Under this crossed area, slide the can into position so that the can is perpendicular to the handle bars. Before tightening the zip ties completely, move the can into the desired position. The light should point at the ground in front of the bicycle as well as forward enough to see any night time traffic, including pedestrians.