The GPIO could control a coin mech for example. They’re not required for arcade machines, but that can be used in certain situations. You can connect, relays, motors, switched, LEDs, and all kinds of other sensors to these pins. These pins allow the Raspberry Pi to control the physical world and take input from it. The Raspberry Pi has very cool 32 pin header on it called GPIO. The combination of RetroPie with the Raspberry Pi is a dream for many retro gamers. The last thing, the gooey filling so to speak, is RetroPie, the emulation system that runs the arcade.
It has wired and wireless networking, 4 USB 2.0 ports, an HDMI port, speaker port, SD Card slot, camera connector, touch screen connector, and lastly, GPIO! It runs on a variant of Debian Linux called Raspbian. The Pi is a full blown computer, running on an ARM chip similar two what modern smart phones and devices use. It’s an incredible device that is incredibly affordable. The Raspberry Pi is a $35 computer that was created for the education community.
Download the Arcade Cabinet Plans Here! Retropie and the Raspberry Pi