Astable Multivibrator

Astable-Multivibrator

📌 Project Overview

This project demonstrates an Astable Multivibrator circuit using the NE555P timer IC.

An astable multivibrator continuously switches between HIGH and LOW states without requiring an external trigger. The output of the 555 timer produces a continuous square-wave signal, which is used to blink an LED.

The circuit is designed and documented using KiCad.

🔧 Components Used

⚡ Circuit Description

The NE555P is configured in astable mode.

The timing components R1, R2, and C1 determine the frequency and duty cycle of the output waveform.

The output from Pin 3 (OUT) of the NE555P is connected to an LED through a 330 Ω current-limiting resistor.

When the 555 output switches HIGH and LOW continuously, the LED turns ON and OFF, producing a blinking effect.

🔌 NE555P Pin Connections

🔗 Circuit Connections

Power Supply

• J1 Pin 1 → VCC
• J1 Pin 2 → GND
• PWR_FLAG is connected to the VCC net.
• PWR_FLAG is connected to the GND net.

Timing Network

• R1 = 1 kΩ
• R2 = 50 kΩ
• C1 = 0.1 µF
• R1 is connected between VCC and Pin 7.
• R2 is connected between Pin 7 and the Pins 2/6 junction.
• C1 is connected between the Pins 2/6 junction and GND.

Output

• Pin 3 (OUT) → R3 (330 Ω)
• R3 → LED
• LED → GND

📐 Working Principle

The NE555 timer operates as an astable multivibrator by repeatedly charging and discharging the capacitor.

Charging

The capacitor charges through:

R1 + R2

When the capacitor voltage reaches approximately 2/3 VCC, the threshold comparator changes state and the discharge transistor turns ON.

Discharging

The capacitor discharges through:

R2

When the capacitor voltage falls to approximately 1/3 VCC, the output changes state again and the discharge transistor turns OFF.

This charging and discharging process repeats continuously.

As a result, Pin 3 produces a continuous square-wave output.

🧮 Frequency Calculation

For a 555 timer in astable mode:

f = 1.44 / ((R1 + 2R2) × C1)