An electronic device used to measure a physical quantity such as temperature, pressure or loudness and convert it into an electronic signal of some kind (e.g a voltage). Sensors are normally components of some larger electronic system such as a computer control and/or measurement system.

Analog sensors most often produce a voltage proportional to the measured quantity. The signal must be converted to digital form with a ADC before the CPU can process it.

Digital sensors most often use serial communication such as EIA-232 to return information directly to the controller or computer through a serial port.