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Pololu Isolated USB-to-I²C Adapter library for Python

www.pololu.com

Summary

This is a Python 3 library that helps interface with the Pololu Isolated USB-to-I²C Adapters.

Supported platforms

This library is designed to run on any Python 3 interpreter that has PySerial or an equivalent library.

Installation

First, install Git, Python 3, and the Python 3 venv module by following the appropriate instructions for your operating system. On Debian-based operating systems, for example, you can run:

sudo apt install git python3-venv

In a shell, run this command to create a Python virtual environment to hold this library and its dependencies.

python3 -m venv ~/myvenv

Run the following command to add the venv to your PATH so you can easily run the python3 and pip3 commands for this virtual environment. You will need to do this every time to start a new shell.

export PATH=~/myvenv/bin/:$PATH

(You can test that this worked by running which pip3.)

Download this code to your system, navigate to this directory, and then run pip3 install . to install this library and PySerial in the virtual environment.

Example code

Here is some example Python code showing how to import the library and read the "Model ID" and "Model Type" registers from a VL53L1X time-of-flight distance sensor:

#!/usr/bin/env python3
import pololu_usb_i2c_adapter
i2c = pololu_usb_i2c_adapter.Adapter('/dev/ttyACM0')
address = 0b0101001
i2c.write_to(address, b'\x01\x0F')
data = i2c.read_from(address, 2)
print(data)

If everything is connected properly, the program should print b'\xea\xcc', confirming that the connected device is a VL53L1X.

The first line of Python code imports the library.

The second line creates an Adapter object and connects to the specified serial port. The port name you have to use here depends on your operating system and the number of other CDC ACM devices that are connected, so you might need to change it.

  • On Windows, the port name will be something like "COM6", and you can determine it by the looking in the "Ports (COM & LPT)" category of the Device Manager. The adapter will either appear as "USB Serial Device" or it will have a descriptive name starting with "Pololu Isolated USB-to-I2C Adapter". You can also change the COM port number using the Device Manager.
  • On Linux, you can run ls /dev/ttyACM* to list the USB serial ports connected to your system. One of these will be the adapter. If you have multiple ports in the list, you might consider using the symbolic links provided in /dev/serial/by-id, which do not depend on the order the devices were plugged in.
  • On macOS, you can run ls /dev/cu.usbmodem* to list the USB serial ports connected to your system. One of these will be the adapter.

The third line sets a variable named adddress to 41. This is 7-bit I²C address of the VL53L1X.

The fourth line writes the bytes 0x01 and 0x0F to the VL53L1X. This tells the VL53L1X that we want to select register 0x10F, which is the model ID. Instead of writing b'\x01\x0F', you can write (0x10F).to_bytes(2, 'big').

The fifth line reads two bytes from the VL53L1X and returns them as a Python bytes object. You can write data[0] or data[1] to get the value of an individual byte as an integer, or you can use the unpack method in Python's struct module to decode the binary data to desired format.

For more documentation, see the comments in pololu_usb_i2c_adapter.py.