The Atari 5200 controllers are well known by its low reliability. Many alternatives to the original controllers have rose along the time  from when the sytem was being sold on stores up to present days when it is possible to find adapters being produced and sold by members of Atari Age community forums. The adapters found today can be either:

a) analog - based on digital potentiometers or

b) digital - based on switched resistors.

Both change resistance in a RC network that is used by the console to convert a time measurement into positional information.

There are other ways to do it, though:

1. Applying a variable voltage on a fixed resistor. The charging time depends upon the RC constant for a given potential difference (voltage). That is pretty much how the trackball works.
2. Detecting the moment the timing capacitor start to charge and hold the voltage low until the correct timing has passed. On the 5200 it is a tricky task, because the capacitors do not receive a pulse (of known time) to discharge. Instead they are held discharged until the CPU generates a pulse internally that releases the charge.

I have figured out the methods above after went through plenty of technical information such as datasheets, books and forum posts. In the meantime I have worked on the design of some alternative controller adapters:

Norris: Adapater for Wii Nunchuck controller.

• Provides vertical/horizontal movement plus 2 buttons. - Keypad functions are provided by tactile switches. - Body composed by 3 PCBs stacked on top of each other
•  Built-in Wii Nunchuck connector on PCB
•  Wire bridges on PCB to hold game faceplates

Hunter: Adapter for Playstation Dualshock controller.

• Provides vertical/horizontal movement plus 2 buttons - Analog sticks can work together or expand to a second connector (for Robotron)
• Directional D-PADs work behave like digital controller on Masterplay adapter
• Numeric Pad emulated by the controller by pressing L2. Worth to mention that emulating the keyboard can be somewhaty tricky too.
• Can emulate behavior of trackball, behaving like the Trackpoint on Thinkpads

Stingray: Adapter for Wii Nunchuck Classic controller

• Basically the same functionality of the Hunter
• Numeric Pad emulated by the controller by pressing ZL
• Built-in Wii Nunchuck connector on PCB

Concept board for StingRay

Second controller (for dual stick games) is connected through P2 Jack. If necessary GND connection wire can be used for one of the triggers of the second controller.