WireLessText Terminal

Embedded Systems Project - Bidirectional Wireless Communication Terminal

Embedded Systems Project

A complete bidirectional text terminal system built with Arduino microcontrollers, featuring multi-tap text input via a 4×3 matrix keypad, real-time display on 16×2 character LCDs, and wireless communication between two nodes. This project demonstrates a complete embedded system with user interface design, wireless communication protocols, and efficient firmware organization.

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Table of Contents

• Project Overview
  • Design Philosophy
  • Project Scope
• Key Features
• Code Structure
• Architecture
• Quick Start
  • Building v1 (IR)
  • Building v2 (HC-12)
• Documentation
• Tech Stack
• Hardware Requirements
• License

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Project Overview

This repository documents a complete embedded system implementation: a bidirectional text terminal with wireless communication. The system has been designed with clear separation between UI logic and transport layers, making it easy to extend and modify.

Design Philosophy

The project emphasizes:

• Separation of Concerns: Clear boundaries between UI logic (keypad, LCD, buffers) and transport logic (IR/RF)
• Code Reusability: Shared core logic between IR v1 and HC-12 v2 implementations
• Protocol Validation: Strict filtering of received data to prevent message corruption
• Educational Value: Well-documented code and architecture for learning embedded systems
• Professional Structure: Clean, maintainable code suitable for portfolio demonstration

Project Scope

The current implementation supports:

• Two Transport Layers: IR (NEC protocol) and RF (HC-12 433 MHz)
• Bidirectional Communication: v2 HC-12 version allows both nodes to send/receive simultaneously
• Multi-tap Text Input: Old-school phone keypad-style input with 800ms timeout
• 32-Character Message Buffer: Real-time editing and transmission
• LCD Status Display: Dual-line display showing message and status information

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Key Features

Core Capabilities Multi-tap Text Input Old-school phone keypad-style input Automatic character commit after 800ms timeout Letter groups mapped to keys 2-8 Space (key 0) and backspace (*) support Message Management 32-character message buffer Real-time editing with preview Character-by-character transmission Backspace for preview cancellation or message deletion

Technical Highlights Dual Transport Layers IR v1: NEC protocol with address validation HC-12 v2: 433 MHz RF with bidirectional serial Shared core UI logic between versions Robust Protocol Strict validation (protocol + address + character) Noise filtering prevents message corruption Printable ASCII (32-126) or 0x08 backspace only

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Code Structure

At its core, the system has two roles: Sender and Receiver. The implementation varies by transport layer:

v1 (IR) - Separate Codes

firmware/v1_ir_terminal/
├── sender_ir.ino      # Sender Arduino code
└── receiver_ir.ino    # Receiver Arduino code

• Two separate firmware files for sender and receiver
• Sender handles keypad input, message buffering, and IR transmission
• Receiver handles IR reception, message buffering, and LCD display
• Unidirectional communication (sender → receiver)

v2 (HC-12) - Symmetric Code

firmware/v2_hc12_terminal/
└── terminal_node_hc12.ino    # Single code for both roles

• One symmetric firmware file that works for both nodes
• Same code handles both sending and receiving simultaneously
• Bidirectional communication (either node can send/receive)
• Each Arduino runs the same firmware image

Note: Despite the different file organization, both implementations share the same core logic:

• Keypad scanning and multi-tap input
• Message buffer management
• LCD rendering and status display
• Only the transport layer (IR vs RF) differs

📸 Photo Placeholder: System block diagram showing sender/receiver roles and data flow

🎥 Video Placeholder: Quick demo showing v1 IR transmission from sender to receiver, then v2 HC-12 bidirectional communication

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Architecture

System Overview

The WireLessText Terminal consists of two Arduino-based nodes that communicate wirelessly:

• v1 (IR): Uses infrared LEDs and receivers with NEC protocol (unidirectional: sender → receiver)
• v2 (HC-12): Uses HC-12 433 MHz RF transceiver modules (bidirectional: either node ↔ either node)

Both versions share the same core functionality: multi-tap text input, message buffering, LCD display, and character-by-character wireless transmission.

Block Diagram

┌─────────────────────────────────┐
│      Arduino Node (Single)      │
│                                 │
│  ┌──────────┐   ┌───────────┐  │
│  │ 4×3      │   │  16×2     │  │
│  │ Keypad   │──▶│  LCD      │  │
│  └──────────┘   └───────────┘  │
│       │              ▲          │
│       ▼              │          │
│  ┌──────────────────────────┐  │
│  │   Core UI Logic          │  │
│  │  - Keypad scanning       │  │
│  │  - Multi-tap input       │  │
│  │  - Message buffer        │  │
│  │  - LCD rendering         │  │
│  └──────────────────────────┘  │
│       │              │          │
│       ▼              ▼          │
│  ┌──────────────────────────┐  │
│  │  Transport Abstraction   │  │
│  │  - sendChar()            │  │
│  │  - receiveChar()         │  │
│  └──────────────────────────┘  │
│       │              │          │
│       ▼              ▼          │
│  ┌──────────┐   ┌──────────┐   │
│  │ IR/RF    │   │ IR/RF    │   │
│  │ Transmit │   │ Receive  │   │
│  └──────────┘   └──────────┘   │
└─────────────────────────────────┘

📸 Diagram Placeholder: Higher-resolution block diagram showing data flow between components

For detailed architecture documentation, see docs/architecture.md.

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Quick Start

Building v1 (IR)

Hardware Setup

1. Assemble two Arduino boards (Uno/Nano) with components listed in hardware/bom.md
2. Follow the wiring diagram in hardware/wiring_ir_v1.md

   📸 Photo Placeholder: Complete wired sender Arduino with keypad, LCD, and IR LED 📸 Photo Placeholder: Complete wired receiver Arduino with LCD and IR receiver 📸 Photo Placeholder: Close-up of IR LED connection with resistor

3. One Arduino becomes the sender (IR LED on pin 9)
4. One Arduino becomes the receiver (IR receiver on pin 9)

Software Setup

1. Install Arduino IDE (1.8.x or later)
2. Install required libraries via Library Manager:
   • IRremote (by Armin Joachimsmeyer or similar)
   • LiquidCrystal (built-in)
3. Upload firmware:
   • Open firmware/v1_ir_terminal/sender_ir.ino and upload to sender Arduino
   • Open firmware/v1_ir_terminal/receiver_ir.ino and upload to receiver Arduino

Operation

1. Power both Arduinos
2. On the sender, type using the keypad (multi-tap input)

   📸 Photo Placeholder: LCD showing message being typed with preview character 📸 Photo Placeholder: Status line showing "TX:'A'" after character commit

3. Messages appear on both LCDs as they are sent/received

   📸 Photo Placeholder: Side-by-side view of sender and receiver LCDs showing synchronized messages 🎥 Video Placeholder: Real-time demo of typing on sender and message appearing on receiver LCD

Building v2 (HC-12)

Hardware Setup

1. Assemble two Arduino boards (Uno/Nano) with components listed in hardware/bom.md
2. Follow the wiring diagram in hardware/wiring_hc12_v2.md

   📸 Photo Placeholder: Complete wired node with keypad, LCD, and HC-12 module 📸 Photo Placeholder: Close-up of HC-12 voltage divider circuit (2.2kΩ + 3.3kΩ resistors) 📸 Photo Placeholder: HC-12 module with antenna connected

3. Important: Use a voltage divider on the HC-12 RX line (HC-12 operates at 3.3V logic, Arduino outputs 5V)
   • See hardware/wiring_hc12_v2.md for voltage divider circuit
4. Each Arduino needs one HC-12 module (symmetric design)

Software Setup

1. Install Arduino IDE (1.8.x or later)
2. Required libraries (all built-in):
   • LiquidCrystal
   • SoftwareSerial
3. Upload firmware:
   • Open firmware/v2_hc12_terminal/terminal_node_hc12.ino and upload to both Arduinos

Operation

1. Power both Arduinos
2. Either node can send/receive messages (fully bidirectional)

   📸 Photo Placeholder: Two nodes showing messages typed simultaneously on both 📸 Photo Placeholder: LCD showing "RX:'A' Ln:03" status when receiving

3. Type on either keypad to send messages to the other node

   🎥 Video Placeholder: Demo showing bidirectional communication - typing on Node A appears on Node B, and vice versa

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Documentation

Document	Description
Architecture	System overview, block diagrams, design decisions, and extension points
Pinout	Complete pin assignments for both IR v1 and HC-12 v2 versions
Protocol	Communication protocol specifications (IR NEC and HC-12 serial)
UI Behavior	User interface details, key mappings, multi-tap behavior, and status messages
Wiring (IR v1)	Step-by-step wiring instructions for IR v1 implementation
Wiring (HC-12 v2)	Step-by-step wiring instructions for HC-12 v2 implementation
BOM	Complete bill of materials with component specifications

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Tech Stack

Software

Component	Version/Details
Arduino IDE	1.8.x or later
IRremote Library	For v1 only (NEC protocol support)
LiquidCrystal Library	Built-in (LCD display)
SoftwareSerial Library	Built-in (for v2 HC-12)

Hardware

Component	Specification
Arduino Board	Uno or Nano (ATmega328P, 5V)
LCD Display	16×2 character LCD (HD44780 compatible)
Keypad	4×3 matrix keypad (12 keys)
IR LED (v1)	940 nm, 5 mm (with 220Ω resistor)
IR Receiver (v1)	VS1838B, TSOP4838, or similar (38 kHz)
HC-12 Module (v2)	433 MHz RF transceiver (with voltage divider)

For complete hardware requirements, see hardware/bom.md.

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Hardware Requirements

Per Node (One Complete Arduino Unit)

Core Components:

• 1× Arduino Uno or Nano (5V)
• 1× 16×2 Character LCD (HD44780 compatible)
• 1× 4×3 Matrix Keypad
• 1× 10 kΩ Potentiometer (LCD contrast)

IR v1 Additional:

• Sender: 1× IR LED (940 nm) + 220Ω resistor
• Receiver: 1× IR Receiver Module (VS1838B or similar)

HC-12 v2 Additional:

• 1× HC-12 433 MHz RF Module
• 2× 2.2 kΩ resistors (voltage divider R1)
• 2× 3.3 kΩ resistors (voltage divider R2)
• Antenna (17.3 cm wire or SMA antenna)

Estimated Cost: $15-30 per node (varies by supplier and version)

📸 Photo Placeholder: Spread of all components laid out on a white background (Arduino, LCD, keypad, IR LED/receiver or HC-12, resistors, wires)

For detailed component specifications and suppliers, see hardware/bom.md.

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License

This project is provided as-is for educational and portfolio purposes.

License: MIT (see LICENSE file if available)

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Acknowledgments

This project demonstrates embedded systems design principles including:

• User interface design for embedded systems
• Wireless communication protocols (IR and RF)
• Firmware organization and code reusability
• Protocol validation and error handling
• Real-time system design with non-blocking algorithms