Fake computer PSU cooling fan

Using Arduino General Electronics
4

  1. TIP120 is too big. Not saying it won't work... but it's like using a sledgehammer to push in a thumbtack. To pull a signal line low, you just need a small signal generic device, like a 2N2222. The FANs RPM sender usually have an "open collector" NPN device that PULLS the signal LOW when the RPM magnetic sensor engages.

  2. Seriously... my advice is to get the right fan and install that.

Any fan that "needs to warm up" is not one that I want keeping my parts cool. That's a sure way to eventually lose more than just the fan.