Raspberry Pi 4 Host custom hardware/software to:

Raspberry Pi 4 stacked & 2 Unicorn HATs

Fully configured Raspberry Pi with Unicorn Header and two Unicorn HAT HDs. The Raspberry Pi will be mounted under the layout with the cable throw the base to the two Unicorns on top. 64 3-pin connectors for PWM/servos can be seen across the front in 4 rows of 16. 60 56 of these outputs will be used to control the aspect of the semaphores on the layout. The fan to cool the Raspberry Pi CPU is plugged into the first connector on the bottom row. Along the right edge of the blue board are headers to bring out 16 GPIO pins as outputs to control 16 LEDs and 1 GPIO pin as input for the fan control button. See Adafruit 16-Channel PWM for details.

Edit: The photo/description above is out of date. See Elements of Stack for the current Raspberry Pi 4.

2 Unicorn displays with signal locations

The Unicorn displays are covered by a schematic of the track. The Unicorns' tri-color LEDs represent the 64 signals around the layout. The red/green does not blind well to make a yellow signal aspect (looks white w/green on left edge). At this time (Dec 2020) 10 of the dual-headed semaphore signals have been on back order for about 18 months. The display is needed to show the aspect of the missing signals.

Edit: Remaining semaphores were received in July 2021.

In the lower left corner are the LEDs representing the CPU temperature (5 step vertical ladder), fan on/off, automatic/manual mode and CPU frequency (high, medium, low).