View Full Version : My rear window defog timer circuit.

12-11-2008, 02:55 AM
Well, my buddy's Acura's timer circuit for his rear window defogger went out. We couldn't find a replacement piece anywhere, and instead of doing it the easy way and just putting in a toggle switch for it, I built him this little guy. It took a bit of engineering, and trial and error before it would work right (because I wasn't using Mosfet, it was hard to get it to stay on long enough).

Well anyways, here's what I came up with. It uses a capacitor and resistors to control how quickly the capacitor discharges. When the button is pressed, the capacitor charges up, and as long as it's charged the first transistor turns on. Once that transistor's on, the 2nd one turns on as well, which completes ground to the defogger relay. The time can be controlled by the 1M ohm rheostat.

(these were before I had added a 2nd transistor and snipped all the leads.. so it's still in build process, but looks almost the same when done, just 2 transistors, lol)

I'm pretty happy I got it to work, that was an SOB.

12-11-2008, 02:58 AM
nice, i did something similar with a auto-light circuit.