3-Lead Analog ECG Monitor

A fully functional analog electrocardiogram (ECG) monitor designed and developed using exclusively analog electronics for signal acquisition, amplification, and filtering. The device captures cardiac electrical activity through three electrodes and outputs a clean ECG waveform for real-time monitoring on an oscilloscope.

🔬 Overview

This project demonstrates the design and implementation of a 3-lead ECG monitoring system built entirely with analog components. The device safely extracts weak bioelectric signals from the human body (10 μV to 5 mV), amplifies them, and filters noise to produce a diagnostic-quality ECG waveform suitable for cardiac monitoring.

Key Specifications

• Signal Range: 10 μV - 5 mV input amplitude
• Frequency Range: 0.5 Hz - 100 Hz (cardiac signal bandwidth)
• Electrode Configuration: 3-lead setup (LA, RA, RL) following Einthoven's Triangle
• Power Supply: Battery-operated (dual 6V Li-Ion) for minimal powerline interference
• Output: Analog signal for oscilloscope display

✨ Features

• High-Precision Instrumentation Amplifier: OP07-based differential amplifier with adjustable gain and excellent CMRR (120 dB)
• Multi-Stage Filtering:
  • 2nd Order High-Pass Butterworth Filter (0.5 Hz cutoff) - removes baseline wander
  • 4th Order Low-Pass Butterworth Filter (100 Hz cutoff) - eliminates high-frequency noise
  • Wien-Robinson Notch Filter (50 Hz) - suppresses powerline interference
• Right Leg Drive (RLD) Circuit: Active common-mode rejection for enhanced noise immunity
• Safety-First Design: Battery-powered operation ensures patient safety
• Custom PCB: Professional PCB layout optimized for low-noise analog signal processing
• 3D-Printed Enclosure: Ergonomic, portable design with proper electrode connections

Signal Processing Stages

1. Instrumentation Amplifier: Extracts differential voltage between LA and RA electrodes with variable gain
2. High-Pass Filter: Removes DC offset and baseline wander (fc = 0.589 Hz)
3. Low-Pass Filter: Eliminates muscle artifacts and high-frequency interference (fc = 100 Hz)
4. Notch Filter: Attenuates 50 Hz powerline noise (fc = 49.8 Hz, Q = 0.67)
5. Right Leg Drive: Inverts and feeds back common-mode signals for active noise cancellation

🔨 Hardware Implementation

PCB Design

• Software: EasyEDA
• Type: Through-hole components for reliability and ease of assembly
• Layout: Optimized for minimal noise coupling and proper grounding

Enclosure

• Manufacturing: 3D printed
• Design: Custom enclosure with cutouts for:
  • Electrode connections
  • Power switch
  • Output leads
  • Potentiometer access for gain adjustment

📊 Testing Results

Breadboard Prototype

• ✅ Successfully captured function generator ECG signals
• ✅ Verified with real human ECG signals
• ✅ Clean waveform with identifiable P, QRS, and T waves

Final PCB Device

• ✅ Improved signal quality over breadboard implementation
• ✅ Reduced noise and interference
• ✅ Portable and user-friendly operation

📁 Repository Structure

├── schematics/              # Circuit diagrams and design files
├── simulations/             # LTspice simulation files and results
├── pcb_design/              # KiCAD/Altium files, Gerber files, BoM
├── enclosure_design/        # 3D CAD models (.STL, .STEP files)
├── documentation/           # Project report, datasheets, calculations
├── testing/                 # Test results, oscilloscope captures
└── README.md               # This file

🚀 Getting Started

Prerequisites

• PCB fabrication service (or equipment)
• Soldering equipment
• 3D printer (for enclosure)
• Standard ECG electrodes with 3.5mm connectors
• Oscilloscope for signal visualization
• 6V Li-Ion batteries (×2)

Building the Device

1. Clone the Repository

   git clone https://github.com/yourusername/ecg-monitor.git
   cd ecg-monitor

2. PCB Fabrication

   • Navigate to pcb_design/
   • Send Gerber files to PCB manufacturer
   • Order components from BoM

3. Assembly

   • Solder components following the schematic
   • Test each stage individually before integration
   • Calibrate gain and notch filter potentiometers

4. Enclosure

   • Print enclosure from enclosure_design/ files
   • Assemble PCB into enclosure
   • Connect battery pack and electrode leads

5. Testing

   • Use function generator with cardiac mode for initial testing
   • Test with real ECG signals
   • Adjust potentiometers for optimal signal quality

👥 Team SocketBurners

• Buddhima Imbulpitiya
• Oshan Imaduwage
• Malinda Illankoon
• Manitha Ayanaja