Timer IC 555This timer IC was introduced by Signetics corporation of U.S. in the year 1972.Features of IC NE555:•Supply voltage range: D.C. 5 to 18V•Current sinking and sourcing capacity: 200mA•High temp. stability.•Timing can be adjusted from microseconds to hours.•Good timing stability against supply voltage variations.•Low cost.•Versatile in operation.

Functional Block Diagram

Pin Connection Diagram

Circuit Diagram

Components

R1 = 10kΩR2 = 10kΩR3 = 560ΩC1 = 10µF9v Battery3 White LEDsWire

Working• Here, the IC is used as an astable multivibrator.

Thus the astable circuit will always keep changing its state and the LED will keep flashing without any external trigger.

• The LED will be “ON” when the capacitor C1 is charging and will be “OFF” when it is discharging.

• The capacitor charges through resistors R1 & R2 and discharges through resistor R2.

• Charging time is given by

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• Discharging time is given by

• The “ON” time & “OFF” time can be adjusted by changing the values of R1,R2 & C1.

• Frequency of oscillations is given by

• Resistor R3 will limit the current through LED.

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