PWM a 3-pin PC fan with an Arduino - Bald Engineer

Use a PNP transistor to PWM a 3-pin PC Fan with an Arduino. Because of how PNP transistors work, you'll need to use a NPN driver as well.

How to control a CPU fan using the Arduino

Arduino Pro Mini 328 - 5V/16MHz - DEV-11113 - SparkFun Electronics

Computer Fan 3 Pin to Motherboard 4 Pin PWM Fan Header Adapter Cable - MODDIY

PWM a 3-pin PC fan with an Arduino - Bald Engineer

PWM a 3-pin PC fan with an Arduino - Bald Engineer

Use Arduino With TIP120 Transistor to Control Motors and High Power Devices - Instructables

How to control a CPU fan using the Arduino

sensor - Arduino controlled PWM PC Fan - Electrical Engineering Stack Exchange

So you want PWM control of your 3-pin fan?, Page 5

PWM a 3-pin PC fan with an Arduino - Bald Engineer

3 pin PC fan - Project Guidance - Arduino Forum