I first was exposed to that technology when I bought an Atari Gran Trak 10 driving game for my beach arcade in 1974. It was used to detect both direction and angular rate of the steering wheel rotation.
There were two infrared leds and two receiving transistors and a light interrupter wheel in between them. The outputs of the receiver transistors was converted to TTL level (five volts for binary 1, zero volts for binary 0) and those outputs were then fed into a J-K flipflop, such that the triggering pulse would assuredly arrive when the other input (I forget their designations) was high when the wheel was spun in one direction, but low when spun in the other. If you saw a wave timing diagram, you could easily see why it would never fail. The rate of motion detection pulse could be provided by either of the receiver transistors. I don't remember the first game to use two of these optical interdiction pairs in a so-called trackball like a mouse does, but it might have been Missile Command.
The only weakness of the trackball implementation was that you could attain maximum speed a little faster in one direction than the other because the trackball and roller shaft were off to one side or the other, and pushing the trackball towards the roller made more reliable frictional contact than pushing it in the away direction.
Edited by AntAltMike, 05 July 2013 - 07:58 AM.