Security alarm system circuit design based on PIR sensor

Usually in the security systems of our homes, shops, offices, etc., for accuracy and reliability, microcontroller solutions with infrared or laser transmitters are usually used, but these methods are more expensive.

In this article, engineers enumerate a simpler microcontroller solution for security alarm systems, which not only saves power consumption, but also achieves low cost. PIR sensor is the abbreviation of Passive Infrared Sensor, and it is also a more cost-effective solution. This scheme is a PIR based security alarm system where PIR sensors are used instead of transmitters or receivers.

Circuit principle of security alarm system based on PIR sensor

The main idea of ​​this circuit is to provide safety. This is based on a PIR sensor with an IC that generates a siren. PIR sensors detect infrared radiation emitted by humans and produce a digital output. This digital output is intended for Arduino UNO.

Then, based on the digital signal from the PIR sensor, the Arduino UNO triggers the UM 3561 siren IC. So when any person is detected it makes a sound.

UM3561 is a ROM IC. It can produce a variety of sirens, such as ambulance sirens, fire truck sirens, police car sirens, and more.

Security alarm circuit diagram based on PIR sensor

NOTE: The circuit diagram shows the oscillator resistance (between pins 7 and 8 of the UM 3561) to be 220Ω, but it is 220KΩ.

The circuit components included in this microcontroller solution are:

(1) PIR sensor;

(2) Arduino UNO;

(3) UM3561 alarm IC;

(4) NPN transistor 2N2222;

(5) Resistance 10KΩ and 220KΩ;

(6) Speaker 8Ω;

(7) Breadboard;

(8) Connecting wire.

Security alarm system circuit design based on PIR sensor

The designed system includes Arduino UNO, PIR sensor, UM3561 IC, speaker, transistor and several resistors. UM3516

IC is siren generator IC. It has 8 pins. The first and sixth pins are the sound effect selection pins. Depending on how they are connected, you can choose between 4 different types of sounds.

In this scheme, pins 1 and 6 are not turned on to generate a siren. Pin 5 is connected to +5V via an NPN transistor (activated by pin 4 of the Arduino UNO).

One end of the 220KΩ resistor is connected to the seventh pin of the UM 3561 IC and the other end is connected to the eighth pin of the IC. The output is taken from the third pin of the IC and connected to the speaker through a resistor and transistor.

The base of the transistor is connected to the output of the IC through a 10KΩ resistor. The transmitter pin is connected to ground, while one end of the speaker is connected to the collector and the other end is connected to +5V. To the PIR sensor, its output is connected to Pin 3 of the Arduino.