 It's the PCF-8574. It is a GPIO expander that runs over I-squared C with two convenient Stem-A-Q-T connectors on it, and this allows you to add up to eight digital inputs or outputs. So you can use these as current syncing LEDs or you can use them as inputs for buttons and switches. I'm essentially running each button to a ground rail, and that ground rail goes to this negative input or ground on the PCF-8574, and then each of these, they're labeled pin zero through seven, run to the other side of each of these switches. As I press buttons on my button board here, I am turning on and off a little print statement here. It is the PCF-8574 GPIO expander with Stem-A-Q-T.