Temperature measurements rely upon thermal conductance, so when a person enters a room they don’t immediately raise the room temperature (unless they happen to be on fire). Ī measurement of IR energy is not the same as measuring temperature. We discussed infrared light when we worked with IR Remote Controls.
This radiation isn’t visible to the human eye because it radiates at infrared wavelengths, below the spectrum that people can see. In this article and the accompanying video we will see how PIR sensors work and we’ll experiment with a very useful PIR Sensor module – the HC-SR501 Passive Infrared SensorsĪny object with a temperature above absolute zero emits heat energy in the form of radiation. Rather it measures infrared energy in a room and is triggered upon a sudden change in it, such as the change that occurs when a warm blooded mammal enters the room. Unlike other sensors which emit and then detect infrared light a PIR sensor does not emit anything. Infrared light can also be used either by reflecting or breaking a beam, many burglar alarm systems work this way And microwaves can also be used to detect items composed of water, and people are mostly water.Īnother way of detecting people, and the one we will be focusing on today, is by using a “Passive Infrared” or “PIR” sensor. We have already seen the HC-SR04 Ultrasonic Sensor, this device can be used to detect an intruder by reflecting an ultrasonic signal back to a sensor. Of course there are a number of ways to detect people. Another common reason to detect the presence of people is for energy-saving lighting systems that only come on when a room is occupied. Burglar alarms and intruder detectors are obvious applications. That rise in heat level experienced when a person enters a room can be detected and used as a trigger for a number of devices.
#RPI ARDUINO SENSORS FULL#
If you’ve ever been crammed into a small room full of people you’ll know exactly what I mean. There is no denying it – human beings are hot stuff! Humans (and animals) radiate body heat to such a degree that the temperature of a room rises when people enter it.
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