ELECTRONIC SENSORS AND TRANSDUCERS

Sensors and transducers, as the name says, senses the external physical environment by varying some of their properties in accordance with their current physical environment. A lot of the sensors are based on few electrical properties like change in resistance (as in photo-resister), capacitance, closing of circuits as in case of photo-diode or something that depends on the phenomena of electromagnetic induction (as in a microphone).

Various types of sensors:

• Light sensor: photo-diode and photo-resisters are excellent way to sense light level. A higher intensity of light increases/decreases the resistance and current (in case of photo- resister and diode respectively). Thus measuring the change, we are able to sense the light intensity.            

• Temperature sensor: Again the easiest type of devices under this category are thermistor and thermocouple. Thermistor is just the temperature varying resister and thermocouple involve a metal junction of two dissimilar metals (a voltage is produced when temperature of any part is changed).

• Position sensor: Simplest type in this category involves potentiometers and (rotary) encoders. Potentiometer is just a resistor with 3 leads (one of the lead is a wiper that is responsible for variable resistance, since its position determines the amount of resistance). Rotary encoders work very differently, for more info see: http://en.wikipedia.org/wiki/Rotary_encoder     

• Sound sensor and transducers: Microphone being the simplest type of sound sensor, which converts sound signals to weak (that's why we need amplifiers) electrical signals. Piezoelectric crystal converts the pressure into electrical signals (they offer much more fun).

This is not by any means a complete list of all sensors but if you try one or two of them, you get the general idea of -- what sensors are and how they can be used in your own electronics projects. There are whole range of sensors (and actuators), some of them using mechanics like : MEMS (micro electro mechanical devices), motion sensors, gps, ir distance sensor and so on.

You can buy these sensors from vendors like adafruit.com. They usually embed a tiny microcontroller chip on the sensor board, so that you don't have to do all those conversions (i.e from current/resistance to light intensity). You just only need to know -- how to communicate with these sensors (via MISO and MOSI sort of protocols). And if you don't then there is another option as well--you can buy these sensors only (without microcontroller chip on board) from vendors like analog.com

You can learn more about these sensors and the one described above by following this link:

(video) https://vimeo.com/album/2801639/video/102042976              

After reading this post, I hope you'd have got a very good idea of what a sensor is and where it can be used.