Sensors

A sensor is the sense-organ of a smart device: it picks up something happening in the physical world and turns it into information a machine can act on. The section opens with an experience every phone user has had. Hold a mobile vertically and the display is vertical; turn it sideways and the display rotates to horizontal. Two sensors make this possible, working as a pair:

• The accelerometer detects the orientation of the phone — which way it is being held.
• The gyroscope (gyro) tracks the rotation or twist of the hand, adding its information to what the accelerometer supplies.

Neither sensor alone gives the full picture; the rotating display is the product of their combined data.

Beyond the phone, sensors are very commonly used for monitoring and observing elements in real-world applications — keeping continuous watch on physical conditions that matter. This is precisely where they connect to the chapter's larger theme: the evolution of smart electronic sensors is contributing in a large way to the evolution of the Internet of Things, and it will lead to the creation of new sensor-based, intelligent systems. Devices can only collaborate intelligently if they can first perceive their surroundings, and sensors are what give them that perception.

The section closes with the key definition. A smart sensor is a device that:

• takes input from the physical environment,
• uses built-in computing resources to perform predefined functions when a specific input is detected, and
• processes the data before passing it on.

The word "smart" is earned by the middle two steps. An ordinary sensor merely measures and forwards raw readings; a smart sensor carries its own computing on board, so it reacts to particular inputs with predefined actions and hands over processed data rather than raw signals. …