The CAN USB dongle is a small USB device that allows us to communicate over the CAN bus from our dev computers. It supports the SLCAN protocol, which allows it to be interfaced as a UNIX socket via SocketCAN (on Linux / Mac OS X).

The CAN USB dongle can also power the CAN bus, which is useful when debugging single boards outside our robots.

Contents

CAN USB Dongle
The CAN USB dongle with micro USB wired (left).

Features

  • CAN interface to communicate with nodes on the CAN bus, with 2 Molex picoblade connectors for daisy chain wiring.
  • Dedicated MCU to translate CAN to SLCAN (Serial-Line CAN) over the USB interface.
  • Power regulator to power a few boards over the CAN bus, useful for debugging single boards outside our robots. Activated by pressing the button for more than 1 second
  • UART interface that adds FTDI-like functionality to the dongle.
  • micro-USB interface used for interfacing the computer, but also used for DFU flashing, activated by pressing the button while wiring the dongle over USB.

Hardware

The board is made up of a small double-sided PCB with 2 copper layers. Schematics and layout are made with KiCad and available on Github. It is powered by a STM32F3 controller, and has a few LEDs indicating status and if the bus is powered by the dongle.

Software

The firmware of the CAN USB dongle is written using ChibiOS RTOS and HAL and is available on Github. It implements CAN to USB translation using the Serial-Line CAN protocol (SLCAN). This allows us to expose the CAN interface as a UNIX socket (with SocketCAN), and the standard candump / cansend can be used.

One major use case of the CAN USB dongle, is flashing our boards over CAN, leveraging the CAN bootloader.

Using the SocketCAN interface, we can also monitor our boards during application execution using UAVCAN tools such as the UAVCAN node monitor or the GUI tool.