5-minute epoxy (hot glue for grownups) or hot glue and gun
wooden sticks or plastic coffee stirrers for mixing and applying epoxies
magnetic reed switch
magnet(ring-shaped for tethering)
LEDs(white and red if law in your state mandates, or your choice)
clear spray enamel(for coating circuit to protect from rain-shorts)
moist paper towel
fine grit sandpaper or sanding block
solderless breadboard for prototyping (optional)
Flickr set available.
Project home page on Sternlab.
Step 1: Prep your materials
Test your LEDs to make sure they work, and work out what your circuit will look like. Since I'm using a 9v battery, I'm using three white LEDs for the front in series wired with four yellow in-series LEDs, and the two sets are wired in parallel (see circuit diagram). See what works best for you, and try it out on the breadboard before you commit to the design on your helmet.
Prep the helmet:
Lightly sand the surface to allow the paint to bond more easily. I also took this opportunity to sand off brand logos from my helmet. Follow the sanding with a thorough wipedown with a damp paper towel or cloth. I'd avoid using any cleaner here, since who knows what chemicals are in it and what they might do to your circuit. Water does just fine. Be sure the helmet is completely dry before doing any painting.