Motion Detector Alarm Circuit Using PIR Sensor


The main idea of this project is when any human, animals or any object come in the range of PIR motion sensor, the buzzer must beep automatically. This circuit can also be implemented any where like staircase or front gate etc., and when the PIR sensor detects person movement it will triggers the buzzer on and beep sound is produced.

This project can plays a important role in saving the electrical energy. A PIR Motion Sensor will automatically detect when someone comes and beeps the buzzer. After a few minutes(adjusted by your desires) if there is no movement detected, the Buzzer will then automatically turned off.

Bill Of Material

1SCHR501PIR motion sensor1
2Power Adapter12 volt1
3Buzzer3.3 volt1

PCB Manufacturer

The pcb of this project is manufactured by JLCPCB. The reasons to choose JLCPCB for pcb manufacturing are:

  • Higher Quality
  • Lower Cost
  • Faster Delivery

If you want to order your pcb from jlcpcb just go through the link below:

PIR Motion Sensor

A passive infrared sensor is an electronic sensor that measures infrared light radiating from objects in its field of view. This type of motion sensor is only the receptor of infrared waves and does not release any infrared beam so they are called passive infrared sensor.

PIR Motion Sensor

Working Principle of PIR motion sensor

All the living beings emits infrared radiation to surrounding. Warmer the object more will be the infrared emission.

The Passive Infrared sensor is a thermal infrared sensor that detects the motion of objects by these infrared radiations variations in environment.

The sensor has two or more equal slots made up of Pyroelectric material that is very sensitive to Infrared. When there are no object in the sensor range, both its slots sense the same amount of Infrared radiations.

When a warm body comes in the range of the PIR motion sensor, it passes through both the slots one after the other. The moment it intercepts the first half of the sensor, a positive differential change is caused between the two halves. Similarly, when it leaves the detection area a negative differential change occurs between both the slots. These changes in the pulses are the indication to the sensor that there is some motion in its detecting zone.

PIR Sensor Working

Modes and Adjustment of PIR Sensor Light


PIR sensor waveform

Normal Modes

When the Passive infrared sensor detects motion, it sets the output to High until a certain predefined time by Potentiometer. This mode is independent of the movements during the output HIGH time. In the figure above, t1 is first motion detected. The output go high when the first motion is detected. t2 and t3 are second and third motion detected but in this case the output is not set high as it falls in delay interval. After the output is set for some predefined time there is fix delay. This mode is also independent of the movements during this fixed delay time. The output is set high for the fourth motion (t4) but the output is not high for t5 as it fall in fix delay time.

Re-Triggering Mode

In this mode when the PIR sensor detects motion, it sets the output to High until a set adjusted time but if it detects motion during its output High state 1, it again triggers the sensor to increase the output high period of the sensor.

In re-triggering mode, t6 is the first motion detected. t7 does not trigger the sensor because it is within the fixed delay interval. t9, t10, t11, which occurs after t8 triggers the sensor, extend the time delay since they occurred within the adjusted delay interval.


Sensitivity Adjust

With the help of sensitivity Potentiometer, We can adjust the working range of this PIR sensor.

At the beginning, you must play with this potentiometer so that you can set the appropriate setting for your desired purposes.

If you increase sensitivity it is beneficial for long range.

If you decrease sensitivity it is beneficial for short range.

Delay Time Adjust

The Delay Time indicates how long the PIR sensor will keep the Output High (ON) after detecting motion.

We can set the delay time from few second to five minutes.

Circuit Diagram

circuit diagram of Motion Detector Alarm Circuit

The above figure is the circuit diagram of Motion Detector Alarm Circuit. It has very simple circuit which contian PIR Motion Sensor, Buzzer and power supply.

PIR sensor

Vcc – Positive terminal of battery ( +12V)

Gnd – Negative terminal of battery.

Data – Positive of Buzzer


+VE terminal – Data of PIR sensor

-VE terminal – negative terminal of battery

Working Principle

We are using 12 Volt power supply and Buzzer of same 3.3 Volt rating. We know that, If we directly connect our Buzzer to 3.3 volt power supply, the buzzer will Beep. But the objectives of this project is to beep the buzzer only when the sensor detects the motion. If we measure the voltage across the data pin of PIR sensor, we get 0 volt when no motion is detected. so, Buzzer does not beep when motion is not detected . And there is 3.3 volt in data pin, when motion is detected. This 3.3 volt is directly given to positive terminal of buzzer. The buzzer will produce the beep sound when motion is detected.

circuit of Motion Detector Alarm Circuit

Youtube Video

Project Images


Recommended For You

About the Author: admin

Leave a Reply

Your email address will not be published.