When enabling the SPI interface in the OS only one chip select pin (CE0, GPIO 8) is enabled. The Unicorn HAT hd library also assumes only one device will be used. To use two Unicorn HATs in the TrainThing the second chip select pin is needed, (CE1, GPIO 7). To enable the second chip select the following line and comment were added to the config.txt file

  • In /boot/config.txt
    • Add 

# Enable SPI1 for output to 2nd Unicorn HAT