I have two broken Ataris (2600 and a 2600 Jr) and plenty of games, but no way to play them or make new games. I wanted to backup my current games as well as make new cartridges for the system.
I am using this card-edge connector from DigiKey to interface with the cartridges and this 3D model to allow me to plop them down onto the reader. An Arduino Nano cycles through the 12-bit addresses while pulling the 8-bit data from each. The data gets sent to a computer via serial over USB, where it gets reconstructed into a binary dump of the cartridge.