Base for Raspberry Pi

A simple base for a Raspberry Pi3/4 computer. Has a spot for a 5V 25mm x 10mm cooling fan.

The design also includes spacers for use with a Pi proto hat. If a hat is used 3/4" 2-56 mounting bolts should be used. For just the Pi, 1/4" will work. They screw into the mounting posts, which should be tapped.

The fan can be powered right from the 5V pin, or controlled by a 2N2222 transistor using a GPIO pin. The standard Pi OS has a dt overlay for this. Just add the following to /boot/config.txt:

dtoverlay=gpio-fan,gpiopin=12,temp=52000

Any GPIO pin can be used, 12 is default
Temp is in millideg C, default is 55000
There is a 10deg C hysterisis for the fan to go off
Pin will be active high.

Use a 680ohm resistor from the GPIO to the base of the 2N2222.