I²C devices require two more pins to work along with power and a ground pin—an SDA (data) and SCL (clock) pin. The details of how these are used is beyond the scope of this book (see the Further reading section for more information), but do know that you can hook multiple devices to the same SDA and SCL pins, so long as the devices have different I²C addresses. The address is a two-digit hex number, that is easy to find for nearly all I²C devices, and in some cases the address can be configured physically on the device.

For this chapter's project, we will be using the TSL2561, which can have two different addresses configured to it. We'll stick with the default, 0x39 (on the Adafruit model) for now.