There are a couple of big problems with the conventional analog joystick system. First of all, the crude analog-to-digital conversion process isn't very accurate, since the system doesn't have a true analog-to-digital converter. This compromises the joystick's sensitivity somewhat. Secondly, the host computer has to dedicate a lot of processing power to regularly "poll" the joystick system to determine the position of the stick. This takes a lot of power away from other operations.
Photo courtesy CH Products The Flighterstick, a modern programmable USB joystick from CH Products, uses the same "hands-on throttle and stick" (HOTAS) system as real fighter jets -- individual buttons have unique shapes and textures so you can identify them by touch.
Joystick manufacturers have addressed these problems in a couple of different ways. One solution is to add a sensitive analog-to-digital converter chip in a specialized game adapter card or in the joystick itself. In this system, the converter spits out digital information directly to the computer, which improves the accuracy of the stick and reduces the work load on the host processor. These new joystick models can usually connect to USB ports, which also improves speed and reliability (see How USB Ports Work for details).
Another solution is to skip the analog potentiometer technology all together. Many newer controllers use optical sensors to read stick movement digitally. The diagram below shows one common system.
In this system, the two shafts are connected to two slotted wheels. Each wheel is positioned between two light-emitting diodes (LEDs) and two photocells (the graphic only shows one photocell, LED pair for simplicity's sake). When light from each LED shines through one of the slots, it causes the photocell on the other side of the wheel to generate a small amount of current. When the wheel rotates slightly, it blocks the light and the photocell doesn't generate current (or it generates less, anyway).
When the shaft pivots, it spins the wheel, and the moving slots repeatedly break the light beam shining on the photocell. This causes the photocell to generate rapid pulses of current. Based on the number of pulses that the photocells have generated, the processor knows how far the stick has moved. By comparing the patterns coming from both photocells monitoring one wheel, the processor can figure out which way the stick is moving. This is the same basic system used in many computer mice. (Check out this site for more information.)
One of the biggest additions to the world of joysticks is force feedback technology. In the next section, we'll find out how these joysticks let you experience the game on a new level.