This app connects to an Blackmagic Atem switcher by an IP address. For each tally an IP address can be provided. The app will send HTTP requests to http://ipaddress/off, or http://ipaddress/red or https://ipaddress/green.
Our custom designed tallies will work together with this. The 3d printed box as well as the electronic schematics and the Arduino project are available from our website.
