CAN Bus DBC Signal Decoder and Analyzer

A Python-based tool for decoding and analyzing CAN bus data from automotive networks using DBC (Database CAN) files.

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Table of Contents

• Overview
• What is CAN Bus?
• What is a DBC File?
• Features
• Project Structure
• Installation
• Quick Start

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Overview

This project provides a complete toolchain for automotive CAN bus analysis:

1. Load DBC database files - Parse message and signal definitions
2. Read CAN log files - Support for Vector ASC format
3. Decode CAN frames - Convert raw bytes to physical values
4. Store and analyze signals - Organize time-series data
5. Export to CSV - Long and wide format support
6. Visualize signals - Publication-quality plots

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What is CAN Bus?

CAN (Controller Area Network) is a robust vehicle bus standard designed for automotive applications.

Key Characteristics:

• Multi-master protocol: Any ECU can transmit
• Message-based: Data organized in frames with IDs
• Real-time: Deterministic message prioritization
• Robust: Built-in error detection and fault confinement
• Efficient: Up to 1 Mbps on standard CAN

CAN Frame Structure:

┌─────────────┬──────────┬─────┬──────────────┬─────┬───────┐
│ Arbitration │ Control  │ RTR │     Data     │ CRC │  ACK  │
│     ID      │   Field  │     │   (0-8 bytes)│     │       │
└─────────────┴──────────┴─────┴──────────────┴─────┴───────┘
  11 or 29 bits    6 bits   1 bit   0-64 bits   16 bits 2 bits

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What is a DBC File?

DBC (Database CAN) files define the structure of CAN messages in a human-readable format.

DBC File Purpose:

• Define message IDs and their names
• Specify signal positions within messages
• Provide scaling formulas (factor, offset)
• Document units (RPM, km/h, °C)
• Include value tables (enumerations)

DBC Signal Definition:

SG_ RPM : 0|16@1+ (0.25,0) [0|8000] "RPM" Gateway
    │     │  │  │   │   │    │   │     │       │
    │     │  │  │   │   │    │   │     │       └─ Receiver
    │     │  │  │   │   │    │   │     └───────── Unit
    │     │  │  │   │   │    │   └─────────────── Max value
    │     │  │  │   │   │    └─────────────────── Min value
    │     │  │  │   │   └──────────────────────── Offset
    │     │  │  │   └──────────────────────────── Factor (scale)
    │     │  │  └──────────────────────────────── Value type (+ = unsigned)
    │     │  └─────────────────────────────────── Byte order (1 = big-endian)
    │     └────────────────────────────────────── Length (bits)
    └──────────────────────────────────────────── Start bit position

Features

Core Functionality

• DBC Parser: Load and validate CAN database files
• ASC Log Reader: Parse Vector ASCII log format
• Frame Decoder: Convert raw CAN data to physical values
• Signal Store: Organize time-series data by signal name
• CSV Export: Long format (database) and wide format (plotting)
• Visualization: Multiple plot types with matplotlib

Advanced Features

• Filtering: By time range, CAN IDs, or signal names
• Statistics: Min, max, mean, count for each signal
• Professional Plots: Publication-ready visualizations
• Error Handling: Graceful handling of malformed data
• Logging: Configurable verbose mode for debugging
• CLI Interface: Comprehensive command-line tool

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Installation

Prerequisites

• Python 3.10 or higher
• pip (Python package manager)
• git (optional, for cloning)

Step 1: Clone or Download

# Clone repository
git clone https://github.com/Hansajith98/can-dbc-analyzer.git
cd can-dbc-analyzer

Step 2: Create Virtual Environment (Recommended)

# Create virtual environment
python3 -m venv venv

# Activate virtual environment
# On Linux/Mac:
source venv/bin/activate

# On Windows:
venv\Scripts\activate

Step 3: Install Dependencies

pip install -r requirements.txt

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Basic Usage

Decode all signals from a CAN log:

python src/main.py --dbc dbc/example_vehicle.dbc --log logs/drive_log.asc

This will:

1. Load the DBC database
2. Read the CAN log file
3. Decode all frames
4. Export to output/decoded_signals.csv
5. Generate plots in output/plots/

View Results

# View CSV in terminal
cat output/decoded_signals.csv | head -20

# Open plots (on Linux)
xdg-open output/plots/

# Open plots (on Mac)
open output/plots/

# Open plots (on Windows)
start output/plots/

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Plot Types

1. Single Signal Plot

• Filename: <signal_name>.png
• Content: Time-series of one signal
• Example: rpm.png shows RPM over time

2. Combined Plot

• Filename: combined_signals.png
• Content: Multiple signals on same axes (dual y-axis if different units)
• Example: Speed and RPM together

3. Subplots

• Filename: subplots.png
• Content: Stacked subplots, one per signal
• Example: RPM, Speed, Temperature stacked vertically

4. Overview Dashboard

• Filename: overview_dashboard.png
• Content: Comprehensive 3-panel view
• Panels: Speed/RPM, Temp/Load, Gear

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Theory Concepts Covered,

CAN Bus Concepts

• Message-based communication
• Arbitration and priorities
• Frame structure (standard vs extended)
• Error detection (CRC, ACK)

DBC Database Format

• Message definitions
• Signal encoding (start bit, length, byte order)
• Scaling and physical units
• Value tables and enumerations

Python Best Practices

• Modular design
• Type hints and dataclasses
• Error handling
• Logging and debugging
• Command-line interfaces

Data Analysis

• Time-series processing
• Statistical summaries
• CSV export formats
• Data visualization

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Author

Deshitha Hansajith
January 2026