Bicycle
iPod Charger
A sidewall dynamo powers both lights and tuneage.
By Mark Hoekstra
After buying an iPod mini a couple of years ago, I started experimenting with
ways of extending its battery life. First I tried the Perfectmate hand-cranked
flashlight/charger, only to find out that it takes up to 20 minutes of cranking
to generate just enough power to boot the device. As well as making me
appreciate how much power today’s lithium-ion batteries can hold, this got
me thinking about other ways to human-power my iPod.
I LIVE IN HOLLAND, WHERE BICYCLES ARE
one of the most popular means of transport.
A typical Dutch bike has the old lighting system, which
consists of front and rear light bulbs powered by
a 6V dynamo that runs off a friction wheel on the
front tire. So I got the idea to open up the flashlight
charger, find out where the dynamo connects to
the PCB, and connect my bike dynamo there.
The iPod mini takes USB-standard 5V and can
80 Make: Volume 11
A
handle up to 6V. The hand-crank charger nominally supplies 6V or a little more. Its battery pack
stabilizes the current it produces, but there’s no
regulator to limit its output voltage. So I needed to
add something to prevent the charger from possibly
damaging the iPod with excess power. I first thought
of a voltage regulator IC like an LM7805, but these
are designed to step power back from much higher
levels. Instead, I simply used a Zener diode, which
Photography by Mark Hoekstra
