💡 Light-Based Messaging with STM Development Boards

🚀 Overview

This project explores an innovative approach to data communication using light signals. By leveraging STM development boards, we demonstrate a seamless embedded system-to-embedded system messaging system. The core objective is to transmit analog data - specifically, readings from an onboard potentiometer (POT) sampled via an ADC—from a Transmitter (Sensor Node - SN) to a Receiver (Central Node - CN).

🔑 Key Features

• 🔘 Push-button-triggered data sampling
• 📡 GPIO-based data transmission using the ‘Bit-Bang’ method
• 💡 Custom Light-of-Things (LoT) Message Protocol with parity checks
• ⚡ Real-time error detection and correction mechanisms
• 👂 Continuous listening mode at the receiver for improved responsiveness
• 📟 LCD display for real-time decoded data output

🏗️ System Architecture

The system consists of:

• 📤 Transmitter (Sensor Node - SN)

  • Equipped with an ADC to sample an onboard POT
  • Transmits the sampled data as a binary message using light pulses (LED)
  • Implements the LoT Message Protocol for structured message transmission
  • Includes a checkpoint mechanism to track transmitted samples

• 📥 Receiver (Central Node - CN)

  • Continuously listens for incoming light-based binary messages
  • Decodes the received data and displays it on an LCD
  • Implements error detection via parity checks
  • Compares received samples with checkpoint messages to ensure data integrity

📜 Light-of-Things (LoT) Message Protocol

The LoT protocol defines two types of messages:

📡 1. Data Message

Transmits sampled ADC values from the Transmitter to the Receiver.

• 🟢 Start-of-Text (SOT) [1-bit] - LED ON for 1s
• 🔵 Message Identifier [1-bit] - LED OFF for 1s (Data Message)
• 📊 Data Packet [16-bit] - Represents ADC value; LED ON (1) / OFF (0) for 500ms
• ✅ Even Parity Bit [1-bit] - Used for error detection
• 🔴 End-of-Text (EOT) [1-bit] - LED blinks rapidly for 1s

🔍 2. Checkpoint Message

Ensures message reliability by tracking sent/received samples.

• 🟢 Start-of-Text (SOT) [1-bit] - LED ON for 1s
• 🟡 Message Identifier [1-bit] - LED ON for 1s (Checkpoint Message)
• 📈 Checkpoint Packet [16-bit] - Represents sample count
• ✅ Even Parity Bit [1-bit] - Ensures data integrity
• 🔴 End-of-Text (EOT) [1-bit] - LED blinks rapidly for 1s

⚠️ Error Detection & Handling

1. ✅ Parity Bit Check - Detects single-bit errors within data packets
2. 📊 Checkpoint Message Verification - Compares expected vs. received samples
   • If mismatch → LED blinks rapidly for 2s (🚨 Error Alert)
   • If match → LED remains ON for 2s (✅ Success)

🎨 Design Choices & Modifications

• 🖧 GPIO ‘Bit-Bang’ Method: Direct GPIO manipulation for binary serial transmission over light signals.
• 🔄 Continuous Listening Mode: The Receiver remains in an always-on state for dynamic responsiveness.
• ✅ Parity Bit Addition: Enhances error detection beyond just missing messages.
• 📟 LCD Display Output: Provides real-time data visualisation.

📂 Project Structure

📂 Light-Based Messaging Project
 ├── 📁 Receiver_Code/   # Contains the Receiver (CN) implementation
 ├── 📁 Sender_Code/     # Contains the Transmitter (SN) implementation
 └── 📄 EEE3096S 2023 CS Project Report WLLCAS004 MKKBOI005 MBWMAT002.pdf

🎯 Project Benefits

✅ Real-time data exchange between embedded systems.
✅ Error detection & correction ensures reliability.
✅ Simple yet effective light-based communication.
✅ Adaptable for various IoT and sensor-based applications.

🔮 Future Improvements

• Implement 🌞 Light-Dependent Resistors (LDRs) for more sophisticated optical reception.
• Improve ⏱️ timing accuracy with hardware-based PWM signals.
• Enhance 📈 data rate and efficiency by optimising transmission protocols.

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