Single 12V PWM Fan ATtiny85 Controller

This is a 12V PWM Fan Controller using ATtiny85, with 5V I2C pins exposed (for optional sensors or a 3/4/8-digit LED display), and an optional 10k linear potentiometer for adjustments.

ATtiny85 both controls the fan PWM, and detects the actual fan RPM via tach pulses (two per full rotation).  The base idea is to use a linear potentiometer to control the fan RPM between a set minimum and maximum, optionally showing the RPM on a display.  If I2C sensors are added, other control methodologies are possible.

Top and bottom sides of the PCB