Using a photodiode we can build a basic automatic street lamp which glows when the sunlight intensity decreases. Check here the working of Photodiode with IR sensor. So, in this way, a photodiode can be used to sense the light raysand maintain the current through the circuit. A photodiode is constructed such that light rays should fall on the PN junction which makes the leakage current increase based on the intensity of the light that we have applied. As we know a PN junction allows small leakage currents when it is reverse biased so, this property is used to detect the light rays. Its construction is similar to the normal PN junction diode but the working principle differs from it. It is a semiconductor device which is used to detect the light rays and mostly used as IR Receiver. The pair of IR LED and photodiode is called IR Sensor. The rays generated by an infrared LED can be sensed by Photodiode explained below. The range of these frequencies are greater than the microwave frequencies (i.e. Now let us see the working principle of these different types of sensors and where it can be seen in our day to day life or its application. As said earlier in order to make them work proper voltage should be applied based on their specifications. We need to select the desired sensor based on our project or application. Let us see the various different types of sensors that are available in the market and discuss their functionality, working, applications etc. Various sensors have different operating ranges which should be considered while working with it else the sensor may get damaged permanently. So, sufficient input voltage should be applied to it. Most of the sensors can’t work independently. But the signal conditioning may not be necessary for all the sensors like photodiode, LDR etc. So, a signal conditioning unit (an amplifier) is used to increase the signal strength. For example, if we consider a microphone it detects the audio signal and converts to the output voltage (is in terms of millivolts) which becomes hard to drive an output circuit. In signal conditioning unit, the output of the sensor may be amplified, filtered or modified to the desired output voltage. In those cases, a signal conditioning unit is used in order to maintain sensor’s output voltage levels in the desired range with respect to the end device that we use. In few cases, a sensor alone may not be sufficient to analyze the obtained signal. The sensor can be defined as a device which can be used to sense/detect the physical quantity like force, pressure, strain, light etc and then convert it into desired output like the electrical signal to measure the applied physical quantity. These sensor acts as eyes, ears, nose of any electrical equipment which senses the parameters in outside world and give readings to devices or Microcontroller. Even the mobiles or smartphones which we daily use will have some sensors like hall sensor, proximity sensor, accelerometer, touch screen, microphone etc. To design automated devices first we need to know about the sensors, these are the modules/devices which are helpful in making things done without human intervention. Most of the things that we use now can be automated.
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