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M. Raghib MalikM. Yasir Jamil KhanMunir Shah

B.E Electronics IVB.E Electronics IVB.E Electronics IVB.E Electronics IV

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An

Introduction to

555

Timer/Oscillator I.C

Backbone Of Modern Electronics

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“A semiconductor device that controls

various modes of on/off states

in electrical systems or circuits. The 555

timer is one of

the most widely used types of integrated

circuits.”

� First introduced around 1971

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Energy storage,

Periodic Waveforms, and

One of the most useful electronic devices

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� Pendulum� Bouncing ball� Vibrating string (stringed instrument)� Circular motion (wheel)� Cantilever beam (tuning fork)

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Three Three Three Three operating modesoperating modesoperating modesoperating modes

Monostable mode: The 555 functions as a "one-shot".

Applications include

�Timers

�Missing pulse detection

�Bounce free switches

�Touch switches

�Frequency Divider

�Capacitance Measurement, etc.

1.1.1.1.

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Astable Free Running mode: as an oscillator.

Uses include

�LED and lamp flashers

�Pulse generation

�Logic clocks

�Tone generation

�Security alarms, etc.

2.2.2.2.

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3.3.3.3.

Bistable mode or Schmitt trigger:

Operate as a flip-flop,

If the DIS pin is not connected and no capacitor is used.

Uses include

�Bounce free latched switches, etc.

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Inside a 555 Timer/Oscillator

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Different

Packages

of

555

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40 LED Bicycle Light

Our ProjectOur ProjectOur ProjectOur Project

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Transistors:

•2N2219A (high speed switches)

The 2N2219A and 2N2222A are silicon planar

Epitaxial NPN transistors. They are designed for

high speed Switching application at collector

current up to 500ma

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•2N2907A(General Purpose Amplifiers and switches):

The 2N2905A and 2N2907A are silicon planar

epitaxial PNP transistors designed for high

speed saturated switching and general

purpose applications

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