LEVEL 0 : Task 13

Task 13: 555 astable multivibrator with duty cycle 60%

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Objective

To design a 555 timer astable multivibrator with a duty cycle of approximately 60%, implement the circuit on a breadboard, and observe the output waveform using a Digital Storage Oscilloscope (DSO).

Introduction

A 555 timer is a widely used integrated circuit in electronics that can operate in three modes:

• Astable mode
• Monostable mode
• Bistable mode

In astable mode, the circuit continuously switches between HIGH and LOW states without any external triggering, producing a square wave output.

This circuit is commonly used in:

• LED flashing circuits
• Pulse generation
• Clock signals
• PWM control circuits

Components Required

• 555 Timer IC
• Resistors (R1 and R2)
• Capacitor (C)
• Breadboard
• Jumper wires
• Power supply (5V or 9V)
• Digital Storage Oscilloscope (DSO)

Astable Multivibrator Circuit

In astable mode, the capacitor continuously charges and discharges through resistors R1 and R2, producing a periodic output waveform.

Important Pins of 555 Timer

Pin	Name	Function
1	GND	Ground
2	Trigger	Starts timing cycle
3	Output	Output signal
4	Reset	Resets the timer
5	Control Voltage	Controls threshold voltage
6	Threshold	Ends timing cycle
7	Discharge	Discharges capacitor
8	VCC	Power supply

Circuit Operation

1. The capacitor charges through R1 and R2.
2. When the capacitor voltage reaches 2/3 of VCC, the output switches LOW.
3. The capacitor then discharges through R2.
4. When the voltage falls to 1/3 of VCC, the output switches HIGH again.
5. This cycle repeats continuously, generating a square wave output.

• resistors used are 5 ohms and 10 ohms

Observation

The output waveform observed on the DSO is a rectangular (square) waveform.
The signal alternates between HIGH and LOW states with a duty cycle close to 60%.

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