bash script to control a small fan from a Pine64 or RockPro64 5v GPIO
usage: fanctl [start|stop|setup|on|off|auto|unauto]
For a 5v fan, you can use a simple 1-transistor interface which only requires two extra parts: a 1k 1/4w resistor, and an all-purpose NPN transistor (2N2222, or NPE123AP, or equivalent)
For a 12v fan, you'll need a 2-transistor design as alluded to by Bald Engineer however his pins may not be the same as your pins, so I've posted a cleaned-up schematic with a corrected, generic pin-out - you'll need to validate your transistor pins before wiring.
If you use the GPIO on pin 40 like I do, then the script has the values for you at the top. Pine64 and RockPro64 use different numbers, so you'll need to change them according to your platform. Any other GPIO will require you to look up the values somewhere else.
Auto mode will start the script up backgrounded in a screen session and watch the system temperature until it exceeds the preset limit of 50c, at which point the GPIO pin will swing high, and hopefully cause your fan to run.
The fan should run for $((5 * $UPDATE)) seconds after the temperature drops below 50c, in order to prevent a lot of on/off cycling, and to give your heatsink some extra cooling love.
In the script, there are two variables that are useful to you:
# which GPIO pin are you using
GPIO=75
# In auto mode, how often (in seconds) do we check for temperature changes?
UPDATE=5