Raspberry Pi 4 Host custom software to:

  • Control the aspect of the semaphore signals
  • Control the four 3-LED signals in the Parking Lot
  • Control cooling fan for the Raspberry Pi 4 based on:
    • CPU temperature
    • CPU clock frequency
    • Push-button - Manual On/Off or Automatic
  • Control the Unicorn HAT display for fan status & signal aspect


Raspberry Pi 4 with two Unicorn HD HATs


Fully configured Raspberry Pi with Unicorn Header and two Unicorn HAT HDs


Raspberry Pi 4 with fan board and Servo HATs


Raspberry Pi 4, fan board, 16-channel PWM/servo HAT, and three 16- channel PWM/servo Bonnets. (Unicorn interface board removed.) Across the "front" are the 64 3-pin connectors for the servos to control the semaphores. The fan is connected to the lower left connection.


Raspberry Pi 4 with 16-channel servo HAT pinout for LED signals and fan control


Raspberry Pi 4 and 16-channel PWM/servo HAT (blue). The fan is connected top left to one of the 16 3-pin connectors. Above a USB connection are 4 3-pin connections for the 3-LED signals and to the right the connector for the fan control push button