arduino-i2c-sniffer

Software implemented i2c/twi sniffer for arduino using python to visualize intercepted data.

Using nano 328p:

• 50khz maximum speed, (100khz is common standard)
• 100-150 bytes per single transfer session.

See sample_data.html for output examples.

Output for each session looks like

Motivation

Hardware oscilloscopes and signal analyzers are too expensive.

Usage

1. collecting

• upload sketch to arduino board
• connect board ground pin to analyzed bus ground
• connect A2 pin to analyzed scl bus, A3 pin to sda bus
• open serial monitor using 57600 bitrate

2. analyzing

• save serial monitor data into text file (like sample_data.txt)
• run python2 convertToHtml.py sample_data.txt >sample_data.html
• open sample_data.html in browser

Description

Arduino sketch twi_sniff - data collector

Data collected on signal line changes. So no consecutive equal states possible.

Sniffer itself is working in sessions mode.

1. it gathers data from pins until buffer overflow or inactivity timeout
   • no serial activity during this period
2. it encodes and sends gathered data to serial port
   • no sampling during this period

This allows to expect more predictable sampling rate and achieve bigger supported data rates.

Sniffer require so both pins must be on the same avr GPIO port, so only one sampling is performed for both pins (and it is more-or-less atomic). See datasheet or just bruteforce options to find acceptable pin pair. Or use pre-configured A2+A3.

Data visualization converter

• convertToHtml.py python2 converter
• style.css common css file for generated html
• svg/* source files for css in-line backgrounds

You may use convertToHtml.py as module to create your more nice data converter or even implement direct serial connection with arduino,

If nothing broken, every data session is converted into html table with

• row with visualization of SDA signal levels
• row with visualization of SCL signal levels
• row with signal interpretation by I2C/TWI protocol (S - start, E - end)

Examples

sample_data.txt and sample_data.txt contain commented test data gathered by me.

Limiting i2c speed

Only required for bus masters.

I'm using Raspberry Pi 2 and arduino nano 328p as i2c masters.

Raspberry Pi with raspbian (or derived)

• edit /boot/config.txt
• add dtparam=i2c2_baudrate=50000
• reboot
• check cat /sys/module/i2c_bcm2708/parameters/baudrate

minimal confirmed by me rate is 5000, default is 1000000.

Arduino using Wire library

• after Wire.begin()d
• Wire.setClock(50000);