A sensor is an electronic device that transfers a physical phenomenon
(temperature, pressure, humidity, etc.) into an electrical signal.

Sensors in Robotics are used for both internal feedback control and external interaction with the outside environment.

Desirable Features of Sensors
• Accuracy.
• Precision.
• Operating range.
• Speed of response.
• Calibration.
• Reliability.
• Cost.
• Ease of operation.

The general idea is that the device consists of a movable tap along two
fixed ends. As the tap is moved, the resistance changes. The resistance
between the two ends is fixed, but the resistance between the movable part and either end varies as the part is moved.
In robotics, pots are commonly used to sense and tune position for sliding and rotating mechanisms.

Switch Sensors
Switches are the simplest sensors of all. They work without processing, at the electronics level. Switches measure physical contact. Their general underlying principle is that of an open vs. closed circuit. If a switch is open, no current can flow; if it is closed, current can flow and be detected.

Principle of Switch Sensors
Contact sensors: detect when the sensor has contacted another object.
 Limit sensors: detect when a mechanism has moved to the end of its
 Shaft encoder sensors: detects how many times a shaft turns by having a switch click (open/close) every time the shaft turns.