Last week, BoingBoing posted a reader's comments about a "DIY bike noisemaker" he'd seen. The apparatus involved a piece of metal, which was wired to a nine-volt battery, which was wired to a small speaker. The metal piece picked up noise from passing chunks of magnet or metal attached to the bike's spokes.
No, I haven't figured out how it's made. I've been scratching my head ever since, with the nagging feeling that both Mr. Wizard (R.I.P.) and my fourth-grade science teacher would be very disappointed in me.
Something electromagnetic is probably going on with this bike noisemaker. I'm not sure exactly what. I suspect that the things wired to the spokes are indeed magnets, and electromagnetic waves, sort of like radio static, are generated as they pass by the needle that's wired to the battery, then sent to the speaker and broadcast... but I don't know for sure. Any other ideas?
This was an impetus to find out more about bike noisemakers, which are actually required in many areas.
The apparatus in the BoingBoing post qualifies as a "striker mechanism," one of several types of bike noisemaker, although the metal needle wired to the battery never makes physical contact with the spokes. The most common type of striker mechanism is a playing card clipped to the bike fork so that it will be flapped by the bike's spokes. But another type of battery-operated noisemaker was common in the early-to-mid 20th century: it was a "motor" mounted under the top bar (see photo above).
This patent application on PatentStorm describes the history of several kinds of noisemakers, some battery-operated and several completely possible to DIY, just as much fun on wheelchairs as on bicycles. The patent application itself (which it wouldn't be nice, or legal, to rip off) seems to be for something vaguely similar to the noisemaker that BoingBoing wrote about, in that it's some kind of battery-operated striker. But it's not the same thing.
Until I come to a greater understanding of electromagnetism, it seems that my girly pink Schwinn will just have to live with playing cards and a hand-bell. Old school is usually just as good as geek... isn't it?
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