Cantern: a DIY, low-cost bike headlight!

single speed bike with crate and bucket mounted to a rear rack, and the cantern shining majestically in the night

A few months ago, I got a bike named Vincent Von Velocipede on Craigslist, and have had a lot of fun adding various accessories to it, to enhance its suburban grocery-getting powers. First up was mounting a milk crate above the rear axle. My friend Emily Velasco and I were brainstorming about what to do next, and I brought up the idea for a headlight housed in a soup can. Emily found the electronics for the job, I found an enchilada sauce can and an old aircraft fresnel lens from Apex in Burbank, and we got to work!

Materials

Here is the parts list, with the links to the listings I bought from:

Part name	Cost
El Pato can	~$2
Aircraft lens (used)	$30
1 watt LEDs (25-pack)	$10.39 total, 0.42 each
Current driver	$5.42
Ni-Cad Battery pack with mini USB charger	$13.99
Barrel jacks and plugs (5 pack)	$9.99, $2 each
Wiring, printer filament and scrap metal	Negligible
Toggle switch	~$2 from hardware store
Total incl. bulk order quantities	$73.81
Total, final	$41.84

OK, that's a bit more expensive than an off the shelf headlight. The lens is by far the biggest cost, and we're exploring cheaper lens alternatives such as sheet magnifiers or parabolic mirrors for subsequent versions of Cantern. The cantern functioned satisfactorily without the lens, and that configuration cost 11.84. Sheet magnifiers, at time of writing, cost anywhere from 2 to 10 dollars, putting a cheaper Cantern at a similar price point to bike headlights sold at big box stores.

Process

The first and most important step in the build was to make enchiladas using the sauce from the can. They were tasty. I then washed and dried the can, and drilled holes in the back for the switch and charging port.

the flat bottom of the can, with a toggle switch and barrel port protruding through it

Next I brought all the electronics over to Emily's workshop for soldering and initial assembly. I had very little soldering experience, so I watched her use proper soldering technique for pretty much all of the joints. She also set the driver to a constant 1.5W, 6V, ~250 mA output, which I didn't know how to do either at the time. The LEDs had two different configurations, one of which powered it directly and one used a resistor to regulate the input current. Since we had the driver, we used the more efficient direct configuration.

looking into the cantern after wiring up the components.

The LED mounts to a piece of scrap aluminum channel that acted as a heat sink, which is attached to the wall of the can using screws. The battery and driver mount to the walls using double sided tape. Having learned from Emily's soldering, I replaced the mini USB connector on the charger with a barrel connector, to make the cantern easier to charge. It was now functional, and all that was left was mounting the lens.

The cantern assembled, with all parts mounted to the can, with the LED turned on.

The lens, with a half inch tall printed ring around it. the threaded cylindrical segment of the lens is used to secure it to the ring.

The assembly of the lens and printed ring, fit into the can. — Please pardon the low quality print and mess in my room.

Cantern has worked quite well, and received a lot of compliments from bus drivers and passers-by. The printed mount is not ideal, and I'm looking forward to future iterations that will improve on this whole project.