A rotary encoder can be found at the heart of several input devices, namely spinners, mice and trackballs. The earliest arcade spinners, such as those found on Pong and Breakout, were just knobs stuck on the shaft of a potentiometer. Movement would typically be calculated by measuring the charge or discharge time of a resistance/capacitive circuit. These knobs could be moved in either direction to a stopping point, they could not perform a full 360 degree rotation.
Later arcade spinners, such as those found in Tempest, Arkanoid and Blasteroids used optically encoded spinners. These spinners could be turned 360 degrees and allowed for very precise movement. Speed could be very precisely controlled by a slow or a fast turn of the spinner. Some games like Tron and Tron: Deadly Disks, would have a spinner alongside a joystick for control. Other games like the Ikari Warriors series actually came with a rotary joystick which would be twisted as well as pushed like an 8-way joystick.
Trackballs and mice function like a pair of spinners being controlled at the same time. The ball can be pushed in any direction and the speed can be fast or slow. The only real difference between a trackball and a mouse is whether you are pushing the ball directly with your hand or are rolling it on a surface as enclosed in a plastic housing. True trackballs tend to allow for faster movement, but more people find mice easier to control. Trackballs can be found in arcade machines like Missle Command, which uses a heavy candlepin-sized ball, in Centipede and in the Golden Tee Golf games, which use smaller and faster balls.
Atari 2600 CX-20 Driving Controller
|Driving Controllers (courtesy of AtariAge forums)|
The 2600 Driving Controller is an electromechanical rotary encoder, with a middle "wheel" with metal tabs making contact with a set of circular contacts above and below the wheel offset from each other. The spokes of the wheel are rather large, making for rather coarse resolution. The Driving Controller has one button and only one can be plugged into each controller port, unlike a pair of paddles.
Since official support for the Atari 2600 ended in 1992, occasionally homebrew developers have included support for the Driving Controller. Stell-A-Sketch, Thrust + DC Edition, Thrust Platinum and the 2007 AtariAge Holiday Cart all have support for the Driving Controller. The 2600 games Asteroids, Omega Race and Sprintmaster have all been hacked by Thomas Jentzsch to support the Driving Controller.
The 2600 Driving Controller was reused by Jeff Minter in Tempest 2000 for the Atari Jaguar. Minter had to make a custom cable because the Jag uses HD-15 connectors and the Driving Controller uses DE-9 connectors, but it did work. There is a hidden setting in the game to use a rotary controller instead og the regular Jag controller. Very fine movement will not register on the Driving Controller, so people have modded the Jag pad or made homebrew rotary controllers with greater resolutions (smaller and more numerous spokes). RetroRGB has the details on how to get the rotary controllers to work in T2K: http://retrorgb.com/jaguartempest.html
Atari CX-22, CX-53 and CX-80 Trak-Balls
|Atari CX-22 Trak-Ball (courtesy of AtariAge forums)|
|Atari CX-53 5200 Pro-Line Trak-Ball (courtesy of gaming.wikia.com)|
The CX-53 is the Trak-Ball for the Atari 5200, and is supported by 12 games. This trackball functions very well with them, especially given that Centipede and Missile Command originally used trackballs. This beast has a pair of numeric keypads, four buttons and start/pause/reset buttons.
|Atari CX-80 Trak-Ball (courtesy of atariwiki.org)|
The CX-80 Trak-Ball was designed in the fashion of the Atari XL computers. Early CX-80s output trackball encoded direction and speed signals and function like the CX-22. Later versions output different signals that are intended to make the trackball work as an Atari ST mouse.
Wico released a trackball for the Atari and other home consoles, but it only emulates a joystick.
Missile Command for the 8-bit Atari computer some of the few games written to use the true trackball mode. However, Thomas Jentzsch hacked the 2600 version of Missile Command to support the CX-22 and the CX-80. Other Atari 8-bit computer games that use the trackball are Final Legacy (partially), Millipede, and Kriss Kross. Other 2600 hacks include Centipede, Challenge of Nexar, Star Wars Arcade, SpaceMaster X7, Reactor and Millipede.
Sega Sports Pad and Mark III Paddle Control
|Sega Sports Pad (courtesy of AtariAge Forums)|
This pad is compatible with an Atari 2600, at least in gamepad emulation mode. There is a smaller version released in Japan for the Japanese SMS that lacks the switches.
|Sega Paddle Control (courtesy of Sega Retro) - Note the button on top|
The paddle does not use a rotary controller for the dial, it uses a potentiometer like an Atari paddle. Strangely enough, even though the Sports Pad uses optical rotary wheels, it is still compatible with the Paddle : http://shinobiman.proboards.com/thread/10424/unfairly-maligned-sega-sports-rocks?page=2 The paddle control has a special chip inside it which converts the "analog" value into a pair of nibbles which are sent over the controller lines to the SMS. The Sports Pad does something very similar, so at least one game is compatible with both controllers.
Arkanoid Controller and Hori Track
The Hori Track was released for the Famicom in Japan and plugged into the Famicom Expansion Port. The device added a trackball on a base with a built-in D-pad. It had a two-position switch to adjust the speed of the ball and a two-position switch to set the ID of the pad. With a splitter, two trackballs could be used. The trackball could not emulate a D-pad, games had to be specifically coded to support it. It was supported in four games : Operation Wolf, US Championship V'Ball, Moero Pro Soccer and Putt Putt Golf (FDS).
|Hori Track (courtesy of Endgadget)|
The Arkanoid Controller is a spinner with a single button. Separate versions exist for the NES and the Famicom. Arkanoid came bundled with the controller, and Arkanoid II for the Famicom also had a controller. Taito's Famicom port of Chase H.Q. is also compatible with the Arkanoid controller.
|NES Arkanoid Controller (courtesy of wikipedia) - The small black cover next to the dial gives access to the trimpot|
|SNES Mouse (courtesy of wikipedia)|
The SNES Mouse is very typical of the mice of this era, a ball mouse with two buttons. Unlike the Sega Mega Mouse, the SNES Mouse does not correspond to controller buttons. It was bundled with a hard plastic mousepad with the activity game Mario Paint. Mario Paint requires the mouse, as does the Japanese only game Mario & Wario and are undoubtedly the best games that use the peripheral.
Most of the SNES PC ports pale in comparison to their PC originals. In some cases like Eye of the Beholder, the SNES mouse moves much more slowly than a PC mouse. In other cases like DOOM, the game runs rather slowly compared to the PC version. Unless you like to sit rather close to the TV, the SNES mouse can be something of a chore. Mario Paint has a three speed setting that can alleviate the default slow speed of the mouse.
I found out that Arkanoid, Doh it Again! supported the SNES Mouse and was eager to see how well it worked. It does not work very well, the mouse speed is constant and cannot be changed. The speed is too slow when the ball gets fast. Using the standard SNES controller gives you speed settings, but they are not functional when using the mouse.