The IO-Expander is a central unit on your Joy-Car, to which most of the sensors are connected. Since the micro:bit does not have enough inputs for all sensors, these are connected to the IO expander. This then communicates with the micro:bit via the I2C interface. This way only two ports of the micro:bit are used. There is even an unused digital output on the IO expander available, which you can use for your own projects and sensors. The IO expander is structured as follows:

FOR EXPERTS: The IO expander is addressed via the I2C address 0x38. It checks the sensors connected to it and returns the results summarized as byte. Each bit stands for one pin of the expander. In case of a corresponding detection the bit of the sensor is set to 1 (True).