There are many different kinds of sensors. There are sensors that measure distance, temperature, wind strength, and direction. The list is almost endless. In almost every case, the sensor will take some sort of measurement and then turn it into a voltage that the BeagleBone Black can measure and programmatically respond to. There are many different interfaces for these measurement devices; over the next few chapters, you'll explore many of them. But to start, you'll learn how to measure distance using sonar and IR sensors.