The Atari 5200 Trak-ball
Inside the Unit
This PCB converts the motion of the trak-ball into an analog input to the controller port. Rolling the ball faster in one direction corresponds to pushing an analog joystick further in the corresponding direction. The board has two circuits that act as tachometers with digital inputs and analog outputs. The ball rolls on two rollers which have slotted encoder wheels attached to them. The encoder wheels rotate between pairs of opto-interrupters which provide input pulses to the tach circuits.
This PCB has all the buttons that are on the controller. The buttons (except for the trigger buttons) are just like the buttons in the 5200 sticks. The rubber buttons have small carbon disks on the bottom that, when pressed, touch the contacts on the PCB thus completing the circuit. Fortunetly the trak-ball has a solid PCB as opposed to the less reliable flex circuits used in the sticks. The 4 trigger buttons are a little different. They use a domed piece of metal which bends down and makes contact when pressed. This gives the trigger buttons more of a positive feel then the other buttons.