The first harsh lesson that every Atari 5200 owner learns is this... the stock controllers suck. The second lesson is that alternatives like the Wico Command Control and the Masterplay Interface are tough to find and even harder to afford. The only solution for the penny-pinching classic gamer is to build a Y-cable, making the system compatible with more readily available, less craptacular controllers. It's easy enough to build a cable for a Wico Command Control if you've misplaced the one that came with the sleek red and black joystick, but Y-cables for PC controllers and Sega Genesis joypads take a lot more work to make. See that jumbled mess of wires to the left of this post? That's a schematic for an adapter that converts digital input from a Sega Genesis controller to the analog signal that the Atari 5200 can understand. The top row of connectors must also be wired out to a 15-pin male port, completing the Y-cable and letting you connect a stock controller for the games that can't be started by pressing a fire button.
Y-cables have more modern applications as well. Don't you hate those stupid classic collections for the Playstation 2 that demand a Dual Shock even though the games themselves were originally designed for a digital controller? No sweat! All you need to do is build a straight Y-cable that lets you plug two controllers into the same port. The games now have the analog controller that they demand, while you've got the digital controller that you need to rack up record-breaking scores. Everybody wins!