The EMC2101 from Microchip/SMSC is fan controller with temperature monitoring and it will take care of all of that for you. Programmable PWM output and tachometer input, with both internal and external temperature sensing, with a 1°C accuracy, it’s a perfect friend for any 3 or 4-pin PC fan you may find.
Four pin PC fans have a power and ground pin (those are red and black) and then two more pins. One of those extra pins, the PWM pin, allows you to set a the speed of the fan. The last TACH pin is for a tachometer output that allows the EMC2101 to monitor the speed of the fan to make sure it’s working as expected. Instead of using an PWM output and counter input on your microcontroller, this chip will take care of that all for you, all over every-day I2C.
Stop breadboarding and soldering – start making immediately! Adafruit’s Circuit Playground is jam-packed with LEDs, sensors, buttons, alligator clip pads and more. Build projects with Circuit Playground in a few minutes with the drag-and-drop MakeCode programming site, learn computer science using the CS Discoveries class on code.org, jump into CircuitPython to learn Python and hardware together, TinyGO, or even use the Arduino IDE. Circuit Playground Express is the newest and best Circuit Playground board, with support for CircuitPython, MakeCode, and Arduino. It has a powerful processor, 10 NeoPixels, mini speaker, InfraRed receive and transmit, two buttons, a switch, 14 alligator clip pads, and lots of sensors: capacitive touch, IR proximity, temperature, light, motion and sound. A whole wide world of electronics and coding is waiting for you, and it fits in the palm of your hand.