i2c-adapter 0.2.4

An easy to use USB to I2C adapter using a Raspberry Pico or similar boards.

A Simple USB to I2C Adapter

The I2C Adapter allows python programs to connect to I2C/QUIIC/STEMMA-QT devices using off the shelf low cost boards such the Raspberry Pico or SparkFun Pro Micro - RP2040. The I2C adapter appears on the computer as a serial port (no device installation required) and acts as a USB to I2C bridge, and this Python package provides an easy to use API to interact with it using high level commands.

For example, the schematic below shows the wiring for the oled_demo.py example where the I2C Adapter is used draw on a SH1106 OLED display using the Luma package.

Highlights

• Provides USB to I2C-master bridge.
• Supports Windows/Mac/Linux.
• Uses low cost low cost off-the-shelf boards as adapters.
• Does not require driver installation (it appears on the computer as standard a serial port).
• Comes with an easy to use Python API.
• Easy to modify/extend and to adapt to new hardware.
• Permissive open source license. Comercial use OK, sharing and attribution not required.

Python API Example

Package installation

pip install i2c-adapter --upgrade

In the example below, we use an I2C Adapter that appears as serial port "COM7" to access an I2C device at address 0x08. First we write a single byte 0x00 and then read 20 bytes. Upon completion, the 'data' variable contains a bytearray with 20 bytes.

from i2c_adapter import I2cAdapter

i2c = I2cAdapter(port="COM7")
i2c_addr = 0x08
assert i2c.write(i2c_addr, bytearray([0]))
data = i2c.read(i2c_addr,  20)
print(data)

In the example below we scan the I2C bus address range 0x00 to 0x7f and look for devices that response to an empty write.

from i2c_adapter import I2cAdapter

i2c = I2cAdapter(port="COM18")
print(f"Scanning I2C bus 0x00 to 0x7f:")
for adr in range(0, 127):
    if i2c.write(adr, bytearray([0]), silent=True):
      print(f"  - Device at 0x{adr:02x}")

LED Status

I2C Adapter state	Raspberry Pi LED state
Idle, waiting for a command.	A short blink every two seconds.
Performing a command.	On.
Firmware flashing mode.	Off

Connecting your I2C Adapter

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IMPORTANT

**Do not to exceed the maximal voltage of your board. If needed, use a bidirectional I2C level shifter such as https://www.adafruit.com/product/5649#technical-details.

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Flash your board with the corresponding firmware from https://github.com/zapta/i2c_adapter/tree/main/firmware/release and connect according to the table below:

	SDA	SCL	Internal Pullups	Max Voltage
Raspberry Pico	GP4	GP5	No	3.3V
Sparkfun Pro Micro RP2040	Qwicc SDA	Qwicc SCL	2.2K	3.3V
Adafruit KB2040	Qwicc SDA	Qwicc SCL	No	3.3V
Adafruit QT Py RP2040	Qwicc SDA	Qwicc SCL	No	3.3V

The wire protocol

See comments in the firmware source code.

For firmware developers

We use Visual Code Studion with the Platformio plug in to develope the firmware. Once you install both, clone this repository https://github.com/zapta/i2c_adapter on your machine and use the Menu | File | Open Folder option to open the firmware/platformio directory in the repository. Platformio take a few minutes do configure your environment and you will be able to edit/compile/upload code. Building firmware releases is done by running the Python script build_envs.py.