Pololu Isolated USB-to-I²C Adapter with Isolated Power

Overview

This USB-to-I²C adapter functions as a bridge between I²C devices and a PC or other USB host, enabling the USB host to serve as an I²C controller and communicate with target devices on the I²C bus. It supports bidirectional communication with clock stretching and I²C clock speeds beyond 1000 kHz.

The adapter provides full galvanic isolation between the USB and I²C sides while optionally providing isolated and regulated 5 V or 3.3 V power at up to 200 mA to the I²C bus. This isolation prevents unexpected current flow between the USB host and the I²C bus and protects the USB host from damaging voltages on the I²C bus (the adapter would be damaged under such conditions, but those voltages would not be able to propagate through to the USB side).

The module features a USB Type-C connector. On the USB side, the adapter acts as a virtual serial port (CDC ACM), so it is recognized by major operating systems (e.g. Windows 10 and later, Linux, and macOS) without requiring any driver installation. This means the adapter can be used with any programming environment that allows writing and reading binary data from a serial port (see the user’s guide for documentation on the communication protocol). We provide a Python library for the adapter to make it easy to get started in Python, and the firmware for the adapter’s STM32C071G8 microcontroller is open source for those who want to understand better how it works or customize the behavior.

The I²C side features a JST SH-style 4-pin connector that is compatible with SparkFun’s Qwiic and Adafruit’s STEMMA QT. It also brings the four I²C pins out to 0.1″-pitch through-holes that are compatible with standard 0.1″ male headers and female headers.

Note: An alternative adapter version is available that does not deliver power from the target and instead requires target power to be supplied separately.

Connections

Pin	Cable color	Function
1	Black	I²C ground (GND); this pin is NOT connected to USB GND
2	Red	I²C output voltage (VCC) — When VCC is enabled (controllable by the “Enable VCC Out” command), this pin supplies 3.3V or 5V power at up to 200 mA to the I²C bus. The voltage level is set by the position of the slide switch at start-up.
3	Blue	I²C data line (SDA)
4	Yellow	I²C clock line (SCL)

The VCC voltage level is selectable via a slide switch on the board and latched at power-up, so changing the switch state while the board is powered will not have any effect until the board is power-cycled or enable is toggled via the “Enable VCC Out” command. You can use the blue (5V) and green (3.3V) output voltage indicator LEDs to identify the voltage level that is being output as those illuminate based on the actual voltage rather than the switch position. Both voltage level indicator LEDs are off when VCC is disabled.

Schematic diagram

Schematic diagram of the Pololu Isolated USB-to-I²C Adapter with Isolated Power.