QR Code Toolkit: Generator & Scanner Interface

🚀 Overview

Welcome to the QR Code Toolkit!

1. A C++ QR Code Generator: Crafted from scratch, this tool takes numeric data and transforms it into a Version 1 QR code, saving it as a PBM (Portable BitMap) image. See it in action in qrgenerator.cpp.
2. STM32 Camera Interface: Code designed for an STM32 microcontroller to interface with a camera module (like the OV7670). This lays the groundwork for a potential QR code scanning application. Check out the setup in main.cpp.

✨ QR Code Generator (qrgenerator.cpp)

This command-line program generates Version 1 QR codes, specifically for numeric input data with 'Medium' error correction.

Core Features:

• Numeric Data Encoding: Converts your input numbers (e.g., "123456789") into the compact binary format required for QR codes.
• Robust Error Correction: Implements Reed-Solomon error correction. For Version 1-M, it generates 10 error correction codewords for 16 data codewords, allowing the QR code to be read even if partially damaged.
• Standard QR Structure Generation:
  • Finder Patterns: The iconic squares at three corners of the QR code.
  • Timing Patterns: Alternating black and white modules that help decoders determine module coordinates.
  • Data & ECC Placement: Meticulously places data and error correction codewords throughout the QR grid according to official specifications.
• Smart Masking: Applies all 8 standard mask patterns to the QR grid. It then evaluates them (using logic in evaluate_symbol) to select the pattern that ensures the best readability.
• Format Information: Encodes crucial details like the error correction level ('M') and the chosen mask pattern ID into the QR code. This information is also BCH encoded for its own protection.
• PBM Image Output: Saves the final QR code as a simple, uncompressed .pbm image file, viewable with most image viewers. See create_image. An example output is 6969696969.pbm.

How It Works: A Peek Under the Hood ⚙️

The generator follows a precise sequence to build your QR code:

1. Input & Initialization:
   • Takes a numeric string as input (e.g., a 9-digit ID from id_generator).
   • Prepares the data with a mode indicator (0001 for numeric) and a character count indicator.
2. Bitstream Assembly:
   • Converts the data to a binary stream.
   • Adds a terminator sequence (0000).
   • Pads the stream to ensure it's a multiple of 8 bits.
   • Adds specific padding codewords (pad_codeword1, pad_codeword2) to reach the 16 data codewords required for Version 1-M.
3. Error Correction Magic:
   • The data codewords are treated as coefficients of a data polynomial.
   • A generator polynomial is used with Galois Field (GF(256)) arithmetic (leveraging log_table and antilog_table) to compute Reed-Solomon error correction codewords.
4. Building the Matrix (21x21 for Version 1):
   • The combined data and error correction codewords are strategically placed within the QR code grid.
   • Essential structural elements like finder patterns and timing patterns are drawn onto the grid.
5. Optimizing for Readability (Masking):
   • The grid is tested against 8 different mask patterns. The "best" pattern (minimizing penalties) is chosen.
   • Format information (error correction level + mask pattern ID) is generated, BCH encoded, and embedded in designated areas of the QR code.
   • A mandatory dark module is added.
6. Saving Your QR Code:
   • The final binary grid is converted into a PBM image by the create_image function.

Usage

To generate a QR code:

1. Compile qrgenerator.cpp using a C++ compiler (e.g., g++).
2. Run the compiled executable.
   • It will typically generate a QR code for a randomly generated 9-digit number (thanks to id_generator) or a hardcoded one if you modify the source.
   • The output will be a .pbm file named after the input data (e.g., 123456789.pbm).

📸 Camera Interface / QR Scanner Foundation (main.cpp)

The main.cpp file shifts focus to hardware, specifically setting up an STM32 microcontroller.

• Hardware Configuration:
  • GPIO Setup: Configures General Purpose Input/Output pins for:
    • A parallel camera interface (D0-D7 data lines, HREF, VSYNC, DCLK).
    • I2C communication (SDA, SCL), often used to configure camera sensors like the OV7670.
  • Peripheral Initialization: Sets up I2C and DMA (DMA_Init) controllers on the STM32.
• Intended Purpose: To capture images using a camera module connected to the STM32, process these images, and decode QR codes. The camera.cpp file might contain further logic for this.

This component is distinct from the generator and would run on the embedded STM32 platform.

🔮 Future Directions & Potential Enhancements

This project has a solid foundation with many exciting possibilities:

• Full Scanner Implementation: Develop the STM32-based QR scanner to capture and decode QR codes in real-time.
• Generator Upgrades:
  • Support for higher QR code versions (larger grids, more data).
  • Implement other error correction levels (L, Q, H).
  • Add encoding for Alphanumeric, Byte, and Kanji data types.
• Integration: Potentially link the generator and scanner components, perhaps for testing or a closed-loop system.

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