Bicycle generator technology has advanced far beyond the bottle dynamos of years past, which as often as not would introduce enough drag when engaged to stall the bike. Granted, it’s not as much of a current draw as a big old incandescent headlight, but this wheel-powered cyclocomputer is a great example of harvesting both power and data from the rotation of a bike’s wheel.
While there are plenty of cyclocomputers available commercially, [Lukas] was looking for some specific features. His main goal was something usable at night, which means a backlit display, ruling out the usually coin-cell power sources. His bike’s hub dynamo offered interesting possibilities — not only does it provide AC power, but its output frequency is proportional to the bike’s speed. This allows him to derive speed, distance, RPM, time-in-motion, and other parameters to display on the 1×8 character LCD display. There’s some clever circuitry needed to condition the output of the hub dynamo, and a 1.5 farad supercapacitor keeps the unit powered for about four days when the bike isn’t in motion.
As for measuring the frequency of the dynamo’s output, [Lukas] simply used a digital input on the MSP430 microcontroller, with a little signal conditioning of course. He also added a barometer chip for altitude data, plus an ambient light sensor to control the LCD backlight. Everything lives in a clever 3D-printed case with a minimalist but thoughtful design that docks and undocks from the bike easily; [Lukas] assures us that a waterproof version of the case is in the works.
We really appreciate the elegance of this design, and the way it uses the data that’s embedded in the power supply. While [Lukas] appears to have used a commercially available generator, we’ve seen other examples of home-brew hub dynamos before — even one that offers regenerative braking.