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 a 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.

Turns out this is not needed AND it causes GPIO pin to be set HIGH. Following lines I added have now been removed.

  • In /boot/config.txt
    • Add 

# Enable SPI1 for output to 2nd Unicorn HAT