Blackmagic Design Blackmagic Studio Cameras Manuel D'installation Et D'utilisation page 32

The example sketch above shows how the Blackmagic 3G-SDI Shield for Arduino is programmed
to detect a tally signal for input 1 or 2 via the switcher's tally output, and then embed that tally signal
into the shield's SDI output. The tally light on the corresponding camera will then illuminate.
Connecting Tally using the Blackmagic 3G-SDI Shield for Arduino 32