Digital and analogue signals
Digital signals are relatively easy to manage - they work in a very similar way to variables in a piece of software. They consist of discrete values which are precisely defined. The value of an analogue signal on the other hand has a continuously-varying value because it corresponds to a real physical quantity.
A tilt sensor like the one shown in Figure 1 is a good example of a simple digital sensor. The metal ball is either in contact with the electrical connections or it is not. There are only two possible states of the sensor which correspond to a Boolean true/false, or a binary 1/0 value.
A photosensitive resistor is a good example of an analogue sensor. Its resistance varies continuously between a minimum and a maximum value depending on ambient light intensity. Because the resistance is a physical quantity, it is infinitely divisible, and this means that the signal can take an infinite number of values depending on the precision of the measurement! This leads to a number of complications in the management of analogue signals.