Digital versus Analog

Some sensors, such as look down sensors, are typically used as binary (digital) sensors. Others, such as the GP2D12 sensors, are analog sensors. A binary digital sensor is one that, from the perspective of software, only produces results of 0 and 1. An analog sensor, on the other hand, produces values that has a range (wider than 0 to 1).

Note that even though phototransistors are analog sensors that has a different $\mathrm{I}_{\mathrm{CE}}$ depending on the amount of IR energy irradiating the die. However, the use of a comparator or schmidt trigger effectively converts the voltage measured from a voltage divider into just 0 and 1.

Binary sensors are easy to interpret, but they do not provide a lot of information, either. On the other hand, analog sensors provide more information, but it requires techniques to fully utilize such extra information. For example, traditionally, lookdown sensors are considered binary. This means either a sensor senses a wall underneath, or it does not sense a wall. Treating a lookdown sensor as an analog sensor (using an ADC), on the other hand, can differentiate a sensor that is entirely outside a wall from one that is right on the boundary. This extra information translates to higher resolution for the sensor bank location, which in return translates to better error correction behavior.