Connecting the Dots with Controller Area Network (CAN) Bus on Raspberry Pi

Explore the basics of CAN bus, its application in automotive systems, and how to use it with a Raspberry Pi. …


Updated August 9, 2023

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Explore the basics of CAN bus, its application in automotive systems, and how to use it with a Raspberry Pi.

Introduction

Controller Area Network (CAN) is a protocol for communication between multiple microcontrollers and electronic control units in vehicles. It has been widely used in the automotive industry since the 1980s and continues to be the preferred choice for connecting different components in modern cars, trucks, and buses due to its robustness, reliability, and cost-effectiveness. This article aims to explain what CAN is, how it works, its applications in vehicles, and how you can use it with Raspberry Pi to build your own projects.

What is CAN Bus?

CAN bus is a serial communication protocol that enables multiple devices to communicate with each other using a shared data link. It was developed by the German automotive manufacturers in the 1980s and has since become an international standard (ISO 118981). The primary advantage of CAN over other communication protocols is its ability to support multi-master architecture, where multiple devices can transmit data simultaneously without collisions. This feature makes it ideal for use in distributed control systems such as automotive networks.

CAN bus uses a differential signaling technique to transmit and receive data. Each device on the bus has a unique identifier (Node ID) that is used to address messages, allowing communication between specific nodes or broadcasting to all nodes. The CAN protocol supports two data rates: 1 Mbit/s and 250 Kbit/s.

Applications of CAN Bus in Automotive Systems

CAN bus plays a crucial role in modern vehicles by linking various electronic control units (ECUs) like engine control modules, brake control modules, transmission control modules, and others. It also connects sensors such as speedometers, fuel injection systems, and airbags to the ECUs for data exchange. Some of its key applications in automotive systems include:

  • Vehicle diagnostics: CAN bus allows monitoring and analyzing various parameters like engine RPM, battery voltage, and vehicle speed in real-time.
  • Engine control: CAN bus is used to communicate with engine management systems for controlling fuel injection, ignition timing, and other functions.
  • Chassis control: It connects devices such as steering angle sensors, wheel speed sensors, and ABS (Anti-lock Braking System) controllers to the ECUs.
  • Entertainment systems: CAN bus enables communication between audio, video, and navigation systems with the central control unit of a vehicle.
  • Safety systems: Airbags, seatbelts, and other safety features are controlled using CAN bus for data exchange between sensors and actuators.

Using CAN Bus with Raspberry Pi

Raspberry Pi is an inexpensive and versatile single-board computer that can be used to build a variety of projects. One of these projects involves connecting it to a CAN bus network for communication with automotive devices or building your own custom sensor nodes. Here’s how you can use Raspberry Pi with CAN bus:

  1. Hardware setup: To interface Raspberry Pi with the CAN bus, you will need an external CAN controller such as MCP2515 or TJA1050. These controllers are available in various breakout boards that can be connected to the Pi’s GPIO pins using a DB9 connector. You will also need a CAN bus transceiver (e.g., SN65HVD23x) to convert the high-voltage signals from the vehicle to the logic levels required by the controller.

  2. Software setup: Once you have connected the hardware components, you can use Python and the SocketCAN library to write a CAN bus communication program for Raspberry Pi. The SocketCAN API provides a user-friendly interface to send and receive data on the CAN bus network using the socket class in Python.

  3. Writing code: To start, you can use the following code template to establish a connection with the CAN bus and send/receive messages:

import socket
import struct

# Create a raw CAN socket
sock = socket.socket(socket.PF_CAN, socket.SOCK_RAW, socket.CAN_RAW)
sock.bind(("can0",))

# Send data to the bus
msg_id = 123  # Set your message identifier
data = [0x01, 0x02, 0x03, 0x04]  # Data bytes
payload = struct.pack("BBBB", *data)
sock.send(struct.pack("=IB3x8s", msg_id, len(payload), payload))

# Receive data from the bus
msg = sock.recv(16)
msg_id, _, dlc, data = struct.unpack("=IB3x8s", msg)
print(f"Received message ID: {msg_id}, Data: {data[:dlc]}")

This code creates a raw CAN socket, binds it to the “can0” interface (assuming you have set up your Pi to communicate with the bus), and sends/receives data using the send and recv methods. Replace the message identifier (msg_id) and data bytes as per your requirements.

  1. Running the code: To run this code, you will need to enable the CAN interface on Raspberry Pi by adding the following line to /boot/config.txt:
dtoverlay=can

Then, reboot the Pi and load the can kernel module using:

sudo modprobe can
sudo modprobe can_raw
sudo modprobe can_dev

After that, you can run your Python program to send/receive data on the CAN bus.

Conclusion

CAN bus is a reliable and widely used communication protocol in automotive systems. Raspberry Pi provides an affordable platform for building projects that require CAN bus communication. By following this guide, you can easily connect your Pi to a CAN network and start exploring its potential applications. With the help of Python and SocketCAN library, you can send and receive data from other devices on the bus, enabling numerous possibilities in areas like automotive diagnostics, telematics, and more.