This Devantech USB to I2C module provides a complete interface between your PC and the I2C bus. The module is self powered from the USB (type-B) cable and can supply up to 70mA at 5V to external circuitry from a standard 100mA USB port. The module is an I2C master only; it cannot act as a slave or in a multi-master bus. The I2C SCL and SDA lines are pulled up to 5V with a 4.7kΩ resistor. If you need to use I2C with a 3.3V device, check out the Devantech I2C, SPI adapter.
The USB-I2C also has ancillary digital and analog IOs. When not using I2C, the device can emulate 1 digital input pin, 2 digital input/output pins, and 2 analog inputs with a 10-bit ADC.
Reading and writing an I2C packet generally follows a specific command structure. Often, one will send a structured packet to the virtual serial port with a I2C-USB command, followed by the I2C device address with address registers and informational bytes. Details and examples on usage can be found using the Downloads tab.