I need hard-drive space over here in Europe so I’m digging through my archives for stuff to delete. Here’s a quick photo series I shot on disassembling the ChampionChip race timer. It’s basically a simple plastic case around a wire coil and an RFID chip:

It works by induction. As you’re running you pass over magnetic plates (usually at the start and end, but they can be used for checkpoints as well). The field induces current in the wire coil which powers the tiny radio transmitter (no batteries) and causes it to emit a unique identification number. The receiving computer logs your start and end transmission times. Subtracting the former from the latter gives your race time.

Simple! Their cost-per-unit is pennies so the chips are given away free and are designed-for-dumpsters. Really, they’re trivial to recycle — good business opportunity! You’d have to go bulk, but you could beat even the pennies-per-unit price from the manufacturers (pennies-per-every-other-unit, eg).

This also implies a small optimization: runners should try to cross the line with their chipped foot forward, and with the chip attached as far forward as possible on their shoe. It also implies a hack: get your chip early, copy the unique ID, write it to another chip, and have someone cross the finish just after you cross the start — run a sub-second 10k!