Joystick Input Device

SimPhonics' Joystick Input Device can be used as a debug tool. For example, the X and Y axis can be used to drive worksheet inputs while the buttons can be used for discrete (BOOLEAN) types. The joystick Input device may also be used for "low end" general purpose analog and digital input. For example, push-to-talk switches and volume control analog signals may be sampled using this input device, which is available on most sound cards.

The PC Joystick, a Bit of History

The joystick model was presented by IBM together with their first IBM PC computer. The joystick was a basic analogue joystick with two buttons. The original joystick interface had circuits for connecting two joysticks, but had only one joystick connector. A special Y-cable was needed if there was need for two joysticks at the same time. Later, some manufacturers put two connectors to their interface card and some card manufacturers implemented only one joystick input. Fortunately, most of the cards today have options for two joysticks like the original IBM joystick card.

The joystick interface card was designed to be as simple and inexpensive as possible. The card consisted of bus interface electronics and four monostable multivibrators (all in on 558 chip). These monostable multivibrators were simple timer circuits which put out a pulse with width directly proportional to the joystick resistance value. The pulse width was then measured using a software loop.

The joystick consists of two potentiometers with variable resistance values between 0 Ohm and 100 kohm (in some joysticks up to 150 kohm). The potentiometer resistances have minimum values when the joystick is at the top left position. One end of the potentiometer is connected to +5V pin and the center pin is connected top the analogue input of the joystick. The other end of the potentiometer is not connected.

Windows95/NT attempts to compensate for these timing and mechanical problems and the result in much better resolution and repeatability than was previously obtainable.

The analog ports are only useful for the least demanding applications, such as volume controls, etc. The buttons however, are discrete and, therefore, usable for these kind of signals.