I2C sniffer project

• Board: STM32F103C8T6 "Blue Pill"
• Pins used:
  • PA9: TX (connect to serial RX)
  • PA10: RX (connect to serial TX)
  • PB8: SCL
  • PB9: SDA
• Serial baud rate: 3 000 000 bits/s
• Additional required hardware: FTDI232 (or similar) USB-to-Serial converter

Project Purpose

This project is built to connect to any I2C network and process any data sent through it in a transparent way. It's useful for debugging faulty networks.

Notes

• This project was built in STM32CubeMX for the free STM32CubeIDE. If you load the project in STM32CubeMX, you can export it to use any other IDE of your choice.

  • You can download the .elf binary file and immediately upload it to the microcontroller using STM32CubeProg or OpenOCD.

• This project sets the processor clock to 72 MHz, the highest one achievable, so that the I2C data can be processed as fast as possible.

• The serial output contains colours. If your terminal doesn't support colours, you might see garbled characters.

• UART is used to output the data. You can connect an FTDI232 USB-to-Serial converter to receive the information. Note that you have to use a converter that supports a baud rate of 3 Mbits/sec.

  The command I used to open the terminal on linux was:

  minicom -s -c on -b 3000000 -D /dev/ttyUSB0
  

  You can also use RealTerm on Windows.

• The HAL driver is used, but all the necessary driver files are included in the Drivers folder.

Important files

• Src/main.c: The source code of the project
• i2c_sniffer.ioc: Open this file inside STM32CubeMX to edit the project.

Screenshot

Schematic

Frequently Asked Questions

Q: Where can I buy the required board for this application?
A: The board needed is the small development board "Blue Pill" for an STM32F1 microcontroller. It costs about 2$ and can be found on common marketplaces like ebay or AliExpress (search for STM32F103C8T6). When getting started with these chips, you will also need an ST-Link device (~2$) available at the same sites, in order to program it.
Finally, an FTDI232 board (~2$) will be needed for serial communication with the Blue Pill.
In total, this sniffer should set you back by less than 6$, if you don't already have the required components.