Let's talk Sensors

As the name suggests, a Sensor simply means something that senses. A sensor acquires a physical parameter and converts it into a signal suitable for processing (e.g. optical, electrical, mechanical). Sensor is similar to a transducer that converts one form of energy into another. In the case of sensors it is converted into electrical signals. Another component we come across is an Actuator which takes electrical signals as an input and converts it into some kind of physical signal. (Image Soure)

Hence, without the use of sensors there would be no automation.

Choice of Sensor

The choice of a sensor depends on the following factors:

• Environmental Factors
• Temperature Range
• Humidity Effects
• Size
• Corrosion
• Over-Range Protection
• Power Consumption
• Ruggedness
• Economic Factors
• Cost
• Durability
• Availability
• Sensor Characteristics
• Sensitivity
• Range
• Stability
• Error
• Linearity
• Response Time

Based on the application and the above factors the perfect sensor for a project is chosen. 

Some Basic Sensors

• Temperature Sensor: The TMP36 is a low voltage, precision centigrade temperature sensor. It provides a voltage output that is linearly proportional to the temperature (in degree Celsius).
• Ultrasonic Sensor: Ultrasonic sensors can be used to solve highly complex tasks involving object detection or level measurement with large precision, because their measuring method works reliably under almost all conditions.
• PIR Sensor: A passive infrared sensor (PIR sensor) is an electronic sensor that measures infrared (IR) light radiating from objects in its field of view. They are most often used in PIR-based motion detectors. (Source)
• Speed Sensor: As name says, measures the speed of the devices mostly transport vehicle.
• Gyroscope: They are used for measuring or maintaining orientation.
• Image Sensor: Based on CMOS technology, used in bio-metrics, security surveillance and consumer electronics.
• Biosensors: Based on Biochemical technology. Used for applications like the electronic tongue, cell testing and other bio-testing applications.

There are many-many sensors available other than these. These are just some examples to make you realize what sensors are. You won't believe there are ready made sensors for a lot many applications and we can develop our own sensors too.