555 Astable multivibrator

🔌 Basic PCB Projects

This repository showcases three foundational PCB design projects created using KiCad, focusing on analog and mixed-signal circuit design for beginners in electronics.
Each project demonstrates schematic design, PCB layout, and practical circuit understanding.

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📘 Projects Included

🟢 1. 5V Regulated Power Supply PCB

This project implements a transformer-based 5V DC regulated power supply designed using the LM7805 voltage regulator IC.
It converts 230V AC mains into a stable 5V DC output, suitable for powering logic circuits, sensors, and microcontrollers.

🔧 Circuit Overview

• AC Input: The supply starts with a 230V AC input through a 230V–12V step-down transformer.
• Protection: A fuse is added in series for overcurrent protection.
• Rectification: A full-wave bridge rectifier is formed using four 1N4007 diodes (D1–D4) to convert AC to pulsating DC.
• Filtering: A large 470µF capacitor (C1) smoothens the rectified DC, while 0.1µF ceramic capacitors (C2, C3) filter out high-frequency noise.
• Regulation: The LM7805 linear voltage regulator provides a constant 5V output even with small input fluctuations.
• Indication: A LED with a 150Ω resistor (R1) indicates when the output is active.

🧠 Key Features

• Converts 230V AC → 12V AC → 5V DC
• Provides clean, regulated 5V output
• Includes protection fuse and indicator LED
• Built entirely with easily available through-hole components

📂 Files Included

• 5V-Regulated-Power-Supply.kicad_sch – KiCad schematic file
• 5V-Regulated-Power-Supply.kicad_pcb – PCB layout file
• 5V-regulated-power-supply-schematic.png – Circuit schematic
• pcb_layout.png – PCB top view
• BOM.csv – Bill of Materials

🧾 Bill of Materials

⚡ Applications

• Embedded systems (Arduino, ESP32, microcontrollers)
• Sensors and small electronic modules
• Prototyping power source

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🟢 2. 555 Timer Astable Multivibrator PCB

This project demonstrates the use of the NE555 timer IC configured in astable mode to generate a continuous square wave output.
The circuit is one of the simplest ways to produce a periodic ON/OFF signal used for LED blinking, clock pulses, or PWM control.

🔧 Circuit Overview

• The 555 timer (U2) is wired in astable configuration — no external trigger is needed.
• R4 and R5 form a resistor network that, along with C3, defines the frequency and duty cycle of the output waveform.
• The DIS and THR pins work together to charge and discharge the timing capacitor (C3), continuously toggling the output.
• C4 is a small decoupling capacitor used to stabilize the control voltage and reduce noise.
• An LED (D2) connected through R6 visually indicates the output oscillation (blinking pattern).

→ Approximate frequency: 720 Hz (LED blinks fast; values can be modified for slower blinking).

🧠 Key Features

• Generates a continuous square wave output
• Adjustable frequency and duty cycle via resistors
• LED output indicator
• Simple, low-cost, and easy-to-solder PCB

📂 Files Included

• 555-timer.kicad_sch – Schematic design file
• 555-timer.kicad_pcb – PCB layout file
• 555-timer-schematic.png – Circuit diagram
• pcb_layout.png – PCB layout image
• BOM.csv – Bill of Materials

🧾 Bill of Materials

⚡ Applications

• LED blinkers
• Clock pulse generation
• Frequency modulation
• Tone generation and PWM circuits

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🔵 3. BJT Astable Multivibrator

A transistor-based astable multivibrator that produces continuous oscillating output without using ICs — ideal for understanding the basic principles of transistor switching.

🔧 Circuit Overview -The circuit consists of two NPN transistors(2N3904), each driving an LED in its collector branch, and connected in a cross-coupled configuration using two capacitors (220 µF each) between the collector of each transistor and the base of the other. -Two pairs of resistors control both the current through the LEDs (1 kΩ at each collector) and the charging rate of the capacitors (5 kΩ at each base). -When one transistor turns on, it pulls its collector low and forward-biases the opposite transistor’s base through the coupling capacitor, turning it off. -This alternating action creates a continuous oscillation: while one LED is ON, the other is OFF, and they toggle back and forth automatically. -The entire circuit is powered by a single 3.7V power supply.

Key Features

• Built using two NPN transistors (2N3904)
• Generates alternating ON/OFF states at both transistor outputs
• Frequency depends on resistor and capacitor values
• Demonstrates transistor biasing and feedback

Files Included

• BJT-Astable-Multivibrator.kicad_sch-shematic design file
• BJT-Astable-Multivibrator.kicad_pcb-PCB layout file
• schematic.png-Circuit diagram
• pcb_layout.png-PCB layout image
• BOM.csv-Bill of materials

🧾 Bill of Materials

Applications

• LED flasher
• Pulse signal generator
• Basic waveform demonstration circuit

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🧰 Tools Used

• KiCad 9.0 – Schematic capture and PCB layout

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📁 Repository Structure

Basic-PCB-Projects/ ┣ README.md ┣ 5V-Regulated-Power-Supply/ ┣ 555-Astable-Multivibrator/ ┗ BJT-Astable-Multivibrator/

🧠 Learnings

• Understood schematic design principles and component selection
• Learned PCB layout techniques: track width, via placement, and routing order
• Gained experience in voltage regulation, oscillators, and transistor switching circuits
• Improved workflow in KiCad file management and PCB documentation

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✍️ Author

Niyathi Arun Kurthkoti
ECE Student | Aspiring Embedded & PCB Design Engineer

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