Application of Passive infrared sensors in home security as well as in automation of room lighting

All human radiates heat in the form of infrared rays (IR), but intensity of this radiation is typically very low. A typical IR sensor cannot detect the presence of human because ambient radiation is always present in surroundings, hence sensor cannot distinguish between radiation coming out of a human and surrounding. Passive infrared sensor is a device which is able to detect the change in IR radiation which may be due to motion of a human. This fact can be implemented on home security system which can be put in sensitive area of home to prevent any intruder disturbance. This circuit can also be used for room lighting control. In both scenarios we may use PIR sensor as a switch.

IR sensors are being used for detection of infrared rays. There are mainly 2 classes of IR sensor.

1. Active IR sensor.

2. Passive IR sensor.

In active IR sensors, energy is radiated in IR region by emitter and then detected by IR sensor after reflection from an obstacle. To the contrary, passive IR sensors directly detect IR radiation coming out of an external source. It is well known that human body also radiates thermal energy in form of infrared. If the strength of IR radiation is very weak then it is a good idea to detect the change in the IR signal. Passive IR sensor (PIR) is able to detect the change in IR signal coming out of a human body. This change may arise by the motion of a human being in the vicinity of PIR sensor. Hence presence of human is possible to be detected by PIR sensor.

When sensor detects any change in IR rays (due to motion of human), the output of op-Amp becomes HIGH and this signal goes to relay switch, suddenly circuit closes and LED glows. For home security purpose we can use a speaker at the output of this sensor. 

Future of Analog-digital hybrid devices for smarter technology:

Most analog device process signal digitally and sometimes we need to convert processed signal back to analog and sometimes we keep processed signal as it is. Hence we can say that there are 2 kinds of analog digital hybrid circuits. First, in which analog signal is processed digitally and a digital output is produced. Second, in which analog signal is processed digitally and a analog output is produced.

As we know Most of the signal which we have to process are analog in nature. Processing of analog signal is difficult task, so we process these signal digitally after analog to digital conversion. This is the reason we need analog-digital hybrid circuit. These type of circuit can respond to our real world, this is the reason that production of such devices could be beneficial for industries in upcoming years as smarter technology is being appreciated by our modern world.