Reading Analogue Signals is very useful in a multitude of applications.
Project 1 - Measuring Voltag.
The Projects in this Book are all about using an external ADC and then Interfacing to a number of sensors to make measurements.
The Raspberry Pi GPIO does not have any Analogue to Digital Converters (ADC) to allow this to be measured directly.
For example many sensors output an Analogue signal that is proportional to the stimuli being measured like temperature, light, pressure and sound level.
Reading Analogue Signals is very useful in a multitude of applications