This project was designed to add tally lights to a Black Magic Designs ATEM switcher. It's designed at a hat for a Raspberry PI. The Pi should be running TBD Production's Black Magic ATEM Raspberry Pi Tally image. The Tally software makes a network connection to the ATEM, pulls the input Program/Preview status, and switches the Pi's GPIO pins to indicate when a given input is in Preview or Program mode. The hat switches voltage from an external power supply to the outputs. Each output can be up to 150mA for a total of 2.8A at 24V. The output connectors are a set of RJ45 jacks, two inputs per jack. Pin 1 is the odd numbered input's Preview ground sink, pins 2 & 3 are positive voltage output, pin 4 is the odd numbered input's Program ground sink. The same pattern repeats for the even numbered input on pins 5-8. One RJ45 has inputs 1 & 2, another has inputs 3 & 4, and so on. The fan is to help cool the Pi.

https://www.tbdproductions.com.au/software/