20 February 2010

Fun with relays

As I mentioned in one of my older posts, some electrical relays arranged in a XOR (eXclusive OR) logic circuit can be used to turn your front turn signals into DRLs (Daytime Running Lights). On my motorcycle, I used a trailer light adapter for plug-n-play simplicity, but that won't work for an old motorcycle with a 6-volt electrical system (modern vehicles, and therefore trailer light adapters, run on 12-volts). So, here is a homebrew alternative using 6-volt relays:
Basically, it allows both lamps to light if you turn on your DRLs, or, one lamp to light if you use your turn signals, or, one lamp to stay steadily-on and the other to flash if you have your turn signal on while your DRLs are activated at the same time (the magic is in the crossed wires seen above connecting the relays together). Normally you'd need four relays for this (two for each side), but a double-pole relay reduces our parts count.

Conveniently, this same logic can let you have three brake lights. Especially on an old 6-volt bike, the brake light can be pretty dim in direct sunlight. If you use red rear turn signals (it's not legal to use amber for brake lights!), you can have all three light up when you hit the brakes, yet still allow one side or the other to flash when you turn your signal on (you'll need another set of three relays separate from your front DRLs of course). Just as DRLs increase rider safety so people ahead of you notice you, triple brakes lights similarly help protect the rider from rear-end collisions by inattentive drivers that might otherwise miss that one little dim brake light.

Now, if only we had an old 6-volt motorcycle to try this out on...

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