The 555 timer

May 14th, 2015
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The 555 timer is an integrated circuit (chip) implementing a variety of timer and multivibrator applications. It was produced by Signetics Corporation in early 1970. The original name was the SE555/NE555 and was called "The IC Time Machine". The 555 gets its name from the three 5-KΩ resistors used in typical early implementations

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555 Paper555 TIMER ICDevoleena Das Department of Electronics & Communication EngineeringAssam Don Bosco Universitydevoassam@gmail.comAbstractThe Apple II microcomputer used a quad timer 558 in monostable (or "one-shot") mode to interface up to four "game paddles" or two joysticks to the host computer. A similar circuit was used in the IBM PC. In the joystick interface circuit of the IBM PC, the capacitor (C) of the RC network (see Monostable Mode above) was generally a 10 nF capacitor. The resistor (R) of the RC network consisted of the potentiometer inside the joystick along with an external resistor of 2.2 kilohms. The joystick potentiometer acted as a variable resistor. By moving the joystick, the resistance of the joystick increased from a small value up to about 100 kilohms. The joystick operated at 5V. Software running in the host computer started the process of determining the joystick position by writing to a special address (ISA bus I/O address 201h). This would result in a trigger signal to the quad timer, which would cause the capacitor (C) of the RC network to begin charging and cause the quad timer to output a pulse. The width of the pulse was determined by how long it took the C to charge up to 2/3 of 5 V (or about 3.33 V), which was in turn determined by the joystick position. Software running in the host computer measured the pulse width to determine the joystick position. A wide pulse represented the full-right joystick position, for example, whi

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