This USB-to-I²C adapter enables a PC or other USB host to act as the controller on an I²C bus, reading and writing data from I²C target devices connected to the bus. It supports clock stretching and I²C clock speeds in excess of 1 MHz. The adapter features complete galvanic isolation between the USB and I²C sides, which prevents unexpected current flow between the two sides and protects the computer and its USB ports from destructive voltages on the I²C bus. This version does not deliver USB power to the I²C bus, so a voltage of 2.25 V to 5.5 V must be supplied on the I²C side.