sensor

A device that measures or detects a real-world condition, such as motion, heat or light and converts the condition into an analog or digital representation. An optical sensor detects the intensity or brightness of light, or the intensity of red, green and blue for color systems. See sensor network and mote.

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(hardware)

sensor - 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.