Attach any I2C clients (Wii Nunchuk, thermo sensor, AD converter, display, relay driver, ...) to your PC via USB ... quick, easy and cheap! Drivers for Linux, Windows and MacOS available.
The i2c-tiny-usb project is an open source/open hardware project. The goal of i2c-tiny-usb is to provide a cheap generic i2c interface to be attached to the USB. It is meant as a replacement for those simple and cheap printer port to I2C adapters. A USB solution has several advantages incl. the built-in power supply and a more future proof interface. Furthermore no cpu intense bitbanging is required on the host side. This USB solution even requires less parts than some printer port solutions.
I2C-Mega-USB is a compatible clone of Till Harbaum’s i2c-tiny-usb. The firmware has no software in common with Till’s implementation but is compatible with the i2c-tiny-usb driver found in the mainline Linux kernel. As a result it will work out of the box without requiring any special software on the host computer. (Even these texts are shamelessly ripped from i2c-tiny-usb and i2c-star, which is a similar project for STM32)
I2C-Mega-USB utilizes ATmega32U4 with hardware I2C and USB, which should be better than the original bitbang I2C and software USB.
The firmware can be easily ported but has been tested on an ATmega32U4 based breakout board (Arduino Leonardo). See LUFA documentatation for possible supported boards. Connections required are:
- USB to host computer
- I2C bus SDA and I2C bus SCL. Add pull up resistors, if needed (for example 2.2kohm resistors to +Vcc). ATmega has internal pull-ups, but they are often considered too weak.
- [Optional: AVR programmer connected via ICSP connector for uploading the firmware
- [Optional: debug only] TX1: UART TX and RX0: UART RX
If you use Arduino module with a bootloader, you can upload the firmware once without problems. After the board boots, the USB Vendor and Product Ids have changed and the serial interface has disappeared. To program the board second time, push the reset button (connect RST to GND) and quickly use avrdude to program the board. Another option is to use a separate programmer (for example USBtinyISP).
ATmega32U4 is often run with 5V voltage, so make sure that your devices can handle it. However if your board provides 3.3V, you may use the pull-up resistors to get 3.3V for SDA and SCL pins, too. I am not an electrical engineer, so I cannot say if this won't damage your board. Works for me, though.
Here's a "BS Micro ATMEGA32U4" board with pull-up resistors and a connected Wii Nunchuk)
- Install avr-gcc compiler toolchain and avrdude. If you have used Arduino IDE, you may have it already (add arduino-x.x.x/hardware/tools/avr/bin/ to PATH).
- Clone this repo:
git clone https://github.com/kasbert/I2C-Mega-USB
- Fetch the libraries:
cd I2C-Mega-USB; git submodule update --init --recursive
- Build the firmware:
make
- Use programmer to install the firmware.
make avrdude
Note that the i2c_dev kernel module needs to be loaded before using any of the
i2c-tools utilities.
Linux users may find useful to allow normal user to access the i2c device.
$ echo 'SUBSYSTEMS=="usb" ATTRS{idVendor}=="1c40" ATTRS{idProduct}=="0534" GROUP="dialout" MODE="0660"'| sudo tee /etc/udev/rules.d/99-i2c-tiny-usb.rules
$ sudo systemctl restart udev
$ i2cdetect -l
...
i2c-9 i2c i2c-tiny-usb at bus 002 device 007 I2C adapter
$ i2cdetect -y 9
# With BMP180 you just might get some data..
$ i2cset -y 9 0x77 0xf4 0x2e
$ i2cget -y 9 0x77 0xf6 i 3
0x75 0x7a 0x00
To make Linux aware of I2C devices on the bus, use the following command:
$ echo bmp085 0x77 | sudo tee /sys/class/i2c-adapter/i2c-9/new_device
$ cat /sys/class/i2c-adapter/i2c-9/9-0077/temp0_input
# BMP085 requires a driver (https://github.com/bsapundzhiev/bmp085)
Where bmp085 is the name of the kernel driver you want to associate with the
I2C device, 0x77 is the I2C device's 7-bit address, and i2c-9 is the bus
number the kernel assigned to the i2c-star adapter (appears as i2c-tiny-usb
in dmesg and i2cdetect).
- i2c-tiny-usb. [https://github.com/harbaum/I2C-Tiny-USB]
- LUFA - The Lightweight USB Framework for AVRs [https://github.com/abcminiuser/lufa/]
- Arduino Core Two Wire Interface [https://github.com/arduino/ArduinoCore-avr/blob/master/libraries/Wire/src/utility/twi.c]
- i2c-star [https://github.com/daniel-thompson/i2c-star]