Here’s a nice little circuit diagram for all those hardcore DIYers if you are trying to build a dual fan controller using an ATtiny45 although I’d never use this thing, I’d rather use a CUBLOC.
"Over the course of a weekend, I cobbled together some leftover robot parts to create a simple dual-fan controller. The board turns on the first fan when the temperature reaches a user-adjustable dial setting, and it turns on a second fan if the temperature exceeds an additional 5 degrees Fahrenheit. With this method, only a single fan is used if the temperature can be kept under control with only one fan, but both fans will kick on if necessary."
