I'm definitely not sure if anyone's done this before, but I've never heard it mentioned before. I got the idea from hearing (I believe it was) ZapWizard and Macroman talking about how fan RPM sensing uses a PWM based signal to report to the motherboard, so I got to thinking that the PWM signal could be used to drive some LEDs to light the fan, instead of using the fans input voltage. I don't have any pics of it, mainly because I don't have a digi camera, but it's as simple as falling off a log. Take four LED's of around 1.5v forward voltage or slightly higher, connect them in series, connect the spare anode to the centre wire on your fan, and the cathode to your fan sensing wire. Didn't make sense to me, I was thinking fan sensing wire to ground, but that didn't work, so... Anyhow, the end result is a group of four LEDs that have their brightness directly controlled by the fan speed, not the input voltage. So if your fan breaks down or is stopped, the LEDs go out. Possibly something someone would have a use for with a CPU fan or maybe with a flow rate sensor that uses a fan header. I havn't tried this with a fan plugged into the motherboard though, so maybe one of the wise ones could comment on the safety of such an undertaking! [Edit] If anyone tries this and has a camera, I'd really appreciate it if they put a pic up. [/edit] [Edit2] Btw, I'm really really sorry about not posting pics, but as explained, no camera. And for the record, they were just bog standard red LEDs, about 1.6 FW voltage, 7 odd MCD. And for some reason, 7 MCD was bright with this. Not super bright, but definitely not as dim as I thought they would be. Anyhoo... [/edit]
I don't really want to rain on your parade... but... I don't know how this is super useful- seeing as how most folks try to mod their fans so that they DONT dim when the speed goes down. I tried myself, but my fans are... irritatingly wired. In any case, props for figuring it out yourself!
Hmm, good point. I was mostly thinking of this hoping to work out a way to have one LED dimmed and another brightened, so you could do a fading from red to blue effect as the fan speeds up, but never got that far. Time to think of something else...
