Blockchain-Based Voting System

🗳️ Blockchain E-Voting Terminal - Firmware

Hardware voting terminal firmware for secure blockchain-based electronic voting system
Built with STM32L432KC microcontroller and ESP32 WiFi bridge over 11 months of solo development.

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Project Overview

This project implements a blockchain-based voting system designed to ensure secure, transparent, and tamper-proof elections. The system leverages the STM32 microcontroller and ESP32 for hardware integration, along with custom-built libraries to manage the voting process and blockchain operations.

🏗️ Hardware Architecture

┌─────────────────────────────────────────────────────────────┐
│                    STM32L432KC (Main MCU)                   │
│  ┌──────────────┐  ┌──────────────┐  ┌──────────────┐      │
│  │   Keypad     │  │   LCD I2C    │  │   R307 FP    │      │
│  │   Input      │  │   Display    │  │   Sensor     │      │
│  └──────┬───────┘  └──────┬───────┘  └──────┬───────┘      │
│         │                  │                  │              │
│         └──────────────────┴──────────────────┘              │
│                            │                                 │
│                            │ UART (115200 baud)              │
│                            ↓                                 │
└────────────────────────────┼─────────────────────────────────┘
                             │
                             ↓
┌─────────────────────────────────────────────────────────────┐
│                ESP32-WROOM-32 (WiFi Bridge)                 │
│                                                             │
│  ┌────────────────┐         ┌────────────────┐             │
│  │  HTTP Client   │ ←────→  │   TLS/SSL      │             │
│  │  JSON Parser   │         │   Encryption   │             │
│  └────────────────┘         └────────────────┘             │
│                            │                                 │
│                            │ WiFi/HTTPS                      │
│                            ↓                                 │
└────────────────────────────┼─────────────────────────────────┘
                             │
                             ↓
                    ┌────────────────┐
                    │  Backend API   │
                    │  (Node.js)     │
                    └────────┬───────┘
                             │
                             ↓
                    ┌────────────────┐
                    │  Hyperledger   │
                    │  Fabric        │
                    └────────────────┘

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✨ Features

Biometric Authentication

• R307 Fingerprint Sensor integration via UART
• Template enrollment with 512-byte capacity
• Real-time matching with adjustable confidence scores
• Support for 1:1 verification mode

Secure Communication

• ESP32 WiFi Bridge handles all network operations
• HTTPS support with TLS 1.2+
• Certificate validation (configurable)
• Command-response protocol via UART
• Automatic retry logic with exponential backoff

User Interface

• 16x2 LCD Display with I2C interface (PCF8574)
• 4x4 Matrix Keypad for Aadhaar/VoterID entry
• Scrolling candidate list navigation
• Real-time status updates and error messages
• Loading animations during network operations

Blockchain Integration

• Direct API calls to Hyperledger Fabric backend
• Vote submission with cryptographic proofs
• Receipt polling with transaction IDs
• Automatic session management
• Email receipt delivery

Security Features

• SHA256 hashing for voter identity
• Fingerprint-based authentication proof
• OTP verification via email
• Auth token-based session management
• No local vote storage (direct blockchain submission)

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🛠️ Hardware Requirements

Component	Model/Spec	Quantity	Purpose
Microcontroller	STM32L432KC (NUCLEO-32)	1	Main voting logic controller
WiFi Module	ESP32-WROOM-32 DevKit	1	Network communication bridge
Fingerprint Sensor	R307 Optical Sensor	1	Biometric authentication
LCD Display	16x2 with I2C (PCF8574)	1	User interface display
Keypad	4x4 Matrix Membrane	1	Data entry (Aadhaar/VoterID)
Power Supply	5V 2A adapter	1	System power
Jumper Wires	Male-to-Female	20+	Connections

Optional Components

• Breadboard or custom PCB
• Enclosure for terminal housing
• Buzzer for audio feedback
• Status LEDs

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🔌 Pin Connections

STM32L432KC Pinout

UART1 - R307 Fingerprint Sensor

PA9  (TX) → R307 RX (Yellow)
PA10 (RX) → R307 TX (White)
         → R307 VCC (Red) → 5V
         → R307 GND (Black) → GND

UART2 - ESP32 Communication Bridge

PA2 (TX) → ESP32 RX (GPIO16)
PA3 (RX) → ESP32 TX (GPIO17)

I2C1 - LCD Display (PCF8574)

PB6 (SCL) → LCD SCL
PB7 (SDA) → LCD SDA
          → LCD VCC → 5V
          → LCD GND → GND

GPIO - 4x4 Keypad Matrix

Rows:
PB0 → Row 1
PB1 → Row 2
PA8 → Row 3
PA11 → Row 4

Columns:
PA0 → Col 1
PA1 → Col 2
PA4 → Col 3
PA5 → Col 4

ESP32-WROOM-32 Pinout

GPIO16 (RX2) → STM32 UART2 TX (PA2)
GPIO17 (TX2) → STM32 UART2 RX (PA3)
GND          → STM32 GND (common ground)

⚠️ Note: ESP32 and STM32 must share common ground. ESP32 runs on 3.3V logic, STM32 UART pins are 5V tolerant.

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Folder Structure

Hardware/
├── BlockchainVotingMX_STM32/
│   ├── Core/
│   │   ├── Inc/                # Header files for STM32
│   │   ├── Src/                # Source files for STM32
│   │   └── Startup/            # Startup assembly files
│   ├── Drivers/                # STM32 HAL drivers
│   ├── Debug/                  # Debugging files
│   └── BlockchainVotingMX.ioc  # STM32CubeMX configuration file
├── Evoting_ESP32/
│   └── Evoting.ino             # Arduino sketch for ESP32
├── LICENSE                     # License file
└── README.md                   # Project documentation

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📱 Usage

First-Time Setup

1. Power on the terminal
2. Enroll fingerprints (admin mode - if implemented)
3. Connect to WiFi - ESP32 auto-connects on boot
4. Verify backend connection - Check LCD for status messages

Voting Flow

┌─────────────────────┐
│  1. SELECT ELECTION │ ← Navigate with keypad (↑/↓/Enter)
└──────────┬──────────┘
           ↓
┌─────────────────────┐
│  2. ENTER AADHAAR   │ ← 12-digit Aadhaar number
└──────────┬──────────┘
           ↓
┌─────────────────────┐
│  3. ENTER VOTER ID  │ ← Alphanumeric Voter ID
└──────────┬──────────┘
           ↓
┌─────────────────────┐
│  4. SCAN FINGERPRINT│ ← Place finger on R307
└──────────┬──────────┘
           ↓
┌─────────────────────┐
│  5. VERIFY IDENTITY │ ← Backend validates with stored template
└──────────┬──────────┘
           ↓
┌─────────────────────┐
│  6. SEND OTP        │ ← OTP sent to registered email
└──────────┬──────────┘
           ↓
┌─────────────────────┐
│  7. ENTER OTP       │ ← 6-digit OTP code
└──────────┬──────────┘
           ↓
┌─────────────────────┐
│  8. VERIFY OTP      │ ← Backend validates OTP
└──────────┬──────────┘
           ↓
┌─────────────────────┐
│  9. SELECT CANDIDATE│ ← Scroll through candidate list
└──────────┬──────────┘
           ↓
┌─────────────────────┐
│  10. CONFIRM VOTE   │ ← Press # to confirm, * to cancel
└──────────┬──────────┘
           ↓
┌─────────────────────┐
│  11. CAST VOTE      │ ← Vote submitted to blockchain
└──────────┬──────────┘
           ↓
┌─────────────────────┐
│  12. WAIT RECEIPT   │ ← Polling blockchain for confirmation
└──────────┬──────────┘
           ↓
┌─────────────────────┐
│  13. SHOW RECEIPT   │ ← Display TX ID and success message
└─────────────────────┘

Keypad Controls

┌───┬───┬───┬───┐
│ 1 │ 2 │ 3 │ A │  A = Up/Previous
├───┼───┼───┼───┤
│ 4 │ 5 │ 6 │ B │  B = Down/Next
├───┼───┼───┼───┤
│ 7 │ 8 │ 9 │ C │  C = Clear/Cancel
├───┼───┼───┼───┤
│ * │ 0 │ # │ D │  # = Enter/Confirm
└───┴───┴───┴───┘  * = Back/Cancel
                    D = Menu (reserved)

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Software Components

• Custom Libraries:
  • esp32_bridge: Manages communication between STM32 and ESP32.
  • keypad: Handles keypad input.
  • sha256: Provides cryptographic hashing.
  • r307: Interfaces with the biometric sensor.
• Blockchain Implementation: Ensures secure and immutable vote storage.

Setup Instructions

1. STM32 Setup:

   • Open the BlockchainVotingMX.ioc file in STM32CubeMX.
   • Generate the code and compile it using STM32CubeIDE.
   • Flash the firmware onto the STM32 microcontroller.

2. ESP32 Setup:

   • Open the Evoting.ino file in the Arduino IDE.
   • Install the required libraries for ESP32.
   • Upload the sketch to the ESP32 board.

3. Hardware Connections:

   • Connect the STM32 and ESP32 using UART.
   • Attach the keypad and biometric sensor to the STM32.

4. Run the System:

   • Power on the hardware.
   • Follow the on-screen instructions to cast votes.

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⭐ Star History

If this project helped you or inspired your work, please give it a ⭐!

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📊 Project Stats

• Lines of Code: ~3000+ (STM32) + ~800+ (ESP32)
• Development Time: 11 months
• Languages: C, C++
• Hardware Platforms: STM32L4, ESP32
• Communication Protocols: UART, I2C, HTTP/HTTPS
• Security: SHA256, TLS, Fingerprint biometrics

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Built with ❤️ and countless cups of coffee ☕

"From concept to completion, every line of code tells a story of persistence."

Contributing

Contributions are welcome! Please fork the repository and submit a pull request with your changes.

License

This project is licensed under the terms of the LICENSE file.

Acknowledgments

• Special thanks to the open-source community for providing tools and libraries that made this project possible.

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