Presentation on flashing LED project using 555 timer IC.

1. Timer IC 555
This 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.

2. Functional Block Diagram

3. Pin Connection Diagram

4. Circuit Diagram

5. Components
R1 = 10kΩ
R2 = 10kΩ
R3 = 560Ω
C1 = 10µF
9v Battery
3 White LEDs
Wire

6. 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
T
 CRRTT COn 21693.0 

7. • 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.
 CRTT DOff 2693.0
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