Previously, I added a USB cooling fan to the X96 Air TV box . The problem with this mod is that the fan is always running, and it runs at full speed. Ideally, the fan should kick in only when the CPU temperature is above a certain threshold. It would be even better if there is a way to control the fan speed. Dan McDonald left me a comment pointing to his project on Github . He basically connected the fan to a USB relay that can be controlled by Python script. His project inspired me to make a similar mod that would make use of the spare D1 Mini boards I have lying around. The plan is to hook up the fan to a MOSFET (2N7000) and control it via PWM. Here's the very simple circuit: The code simply reads a single character from the serial port (0 - 9). 0 will turn the fan off, while 1 - 9 will generate a proportional PWM to drive the fan, with 1 being the lowest and 9 being the highest. Here's the Arduino code: #include <Arduino.h> void setup () { Serial . begin ( 9600