PIR Sensor Circuit And Module Working

A sensor is used to detect the changes in quantities or events and generate the respective output signals such as an electrical signal output or optical signal output. The sensors are classified into various types, but, primarily the sensors can be categorized into analog sensors and digital sensors.

The various types of sensors include temperature sensors, pressure sensors, gas sensors, fire sensors, pyroelectric sensors, piezoelectric sensors, IR sensors, PIR sensors, and so on. Here, in this article we specially discuss about PIR sensor – circuit – module and its working.

PIR Sensor

The electronic sensor used to detect the movement of human being within a certain range of the sensor is called as PIR sensor or passive infrared sensor (approximately have an average value of 10m, but 5m to 12m is the actual detection range of the sensor). Fundamentally, pyroelectric sensors that detect the levels of infrared radiation are used to make PIR sensors. There are different types of sensor and here let us discuss about PIR sensor with dome shaped Fresnel lens.

The PIR sensor circuit is used in numerous electronics projects which are used to discover a human being entering or leaving the particular area or room. These passive infrared sensors are flat control, consists of a wide range of lens, and PIR sensors can be easily interfaced with electronics circuits.

The pin configuration of the PIR sensor is shown in the figure. PIR sensor consists of three pins, ground, signal, and power at the side or bottom. Generally, the PIR sensor power is up to 5V, but, the large size PIR modules operate a relay instead of direct output. It is very simple and easy to interface the sensor with a microcontroller. The output of the PIR is (usually digital output) either low or high.

PIR Sensor Circuit

The PIR sensor circuit consists of three pins, power supply pin, output signal pin, and ground pin. The PIR sensor circuit is having ceramic substrate and filter window as shown in the figure and also having dome like structure called as Fresnel lens.

PIR Sensor Working

Whenever, human being (even a warm body or object with some temperature) passes through the field of view of PIR sensor, then it detects the infrared radiation emitted by a hot body motion. Thus, the infrared radiation detected by the sensor generates an electrical signal that can be used to activate an alert system or buzzer or alarm sound.

The PIR sensor internally is split into two halves, one half is positive and the other is considered as negative. Thus, one half generates one signal by detecting the motion of a hot body and other half generates another signal. The difference between these two signals is generated as output signal. Primarily, this sensor consists of Fresnel lens which are bifurcated to detect the infrared radiation produced by the motion of hot body over a wide range or specific area.

If once the sensor gets warmed up, then the output remains low until it detects motion. If once it detects the motion, then the output goes high for a couple of seconds and then returns to a normal state or low. This sensor requires settling time, which is characteristically in the range of 10 to 60 seconds.

Practical Applications of PIR Sensor

PIR sensors have numerous applications in different fields such as automatic switching operation of outdoor lights, lift lobby, common staircases, automatic switching operation of garden lights based on the presence of a human being, for covered parking area, automatic door operating system in shopping malls, and so on. Let us discuss about a few innovative electronics projects designed using a PIR sensor circuit.

PIR Sensor based Automatic Door Opening System

The automatic door opening system is an innovative electronic project that is designed using PIR sensor. If any human passes through the door, then the sensor generates output pulses. These pulses are sent to the microcontroller which is used to control the operation of motor driver. This motor driver is controlled by microcontroller by giving appropriate pulses to the input and enable pins.

Thus, the motor driver controls the motor interfaced to it and fixed to the door. Hence, if the circuit detects any human passing in its region will enable the motor to operate the door automatically.

PIR Sensor based Security Alarm System

The main principle of the circuit is to provide security. This is based on PIR sensor with an IC that produces siren. The PIR sensor detects the IR radiations emitted from the humans and it produces a digital output. This digital output is applied to the UM 3561 siren IC. Thus it produces the sound when any human is detected.

The UM3561 is a ROM IC. It generates multi siren tones like ambulance siren, fire engine siren, police siren, machine gun sound.

Circuit Diagram:

PIR Sensor based Security Alarm Circuit Design:

The proposed system mainly consists of PIR sensor, UM3561 IC, Speaker, transistors. The UM3516 IC is a Siren generator IC. It has 8 pins. Fifth and sixth pins are shorted and are connected to the PIR sensor output through a resistor. One end of the 220K resistor is connected to the seventh pin of the IC and the other end is connected to the eighth pin of the IC. The first pin and the sixth pin are tone selection pins and these pins decide the tone to be produced. Output is taken from the third pin of the IC. It is connected to a speaker through a resistor and transistor. The base of the transistor is connected to the output of the IC through a resistor of 470 ohms. Emitter pin is connected to the ground while transistor is connected to the collector. A battery is connected to the speaker and 470 ohm resistor.

Working of PIR Sensor based Security Alarm System:

Switch on the circuit initially.
The PIR sensor is powered and it detects the IR rays emitted from any human.
This PIR sensor has a range of 5meters. One can adjust the pot provided for the sensor to vary this distance.
When any human is detected, this PIR sensor outputs a logic high value i.e. voltage of 3.5v to 5v.
This voltage is applied as input to the siren generator IC.
The siren generator has an oscillator internally, to produce the sound.
The oscillator circuit is tuned to a certain frequency and using a 220K resistor externally.
Then it is passed to the control circuit, which depends on tone selection pins.
These tone selection pins decide one tone from different tones produced by the IC.
Thus oscillations along with selected tone are sent to the address counter. The address counter then sends the data to the ROM.
ROM then sends the tone on the output pin 3.
The output is given to the NPN transistor to amplify the siren.
The base of the transistor gets voltage from output pin of the siren generator.
Transistor starts conducting when it gets the cutoff voltage at the base and the speaker is negative pin and is connected to the ground.
Thus sound produced can be heard from the speaker when human is detected.
In the present circuit, it produces fire engine sound.

PIR Sensor Circuit And Module Working