Important Concepts You Must Know For Making PIR Projects


PIR sensor

PIR Project

passive infrared sensor (PIR sensor) is an electronic sensor that measures infrared (IR) light radiating from objects in the field of view. They are often used in PIR-based motion detectors.

Working Principle

All objects with a temperature above absolute zero emit heat energy in the form of radiation. Usually this radiation isn’t visible to the human eye because it radiates at infrared wavelengths, but it can be detected by electronic devices designed for such a purpose.


Infrared radiation enters through the front of the sensor, called as the ‘sensor face’. At the core of a PIR sensor is formed of solid state sensor or set of sensors which is made from pyroelectric materials—the materials which generate energy when exposed to heat. In general, the sensors are approximately 1/4 inch square (40 mm2), and take the form of a thin film. A PIR sensor is formed of materials like caesium nitrate (CsNO3), gallium nitride (GaN),  polyvinyl fluorides, derivatives of phenylpyridine, and cobalt phthalocyanine. The sensor is often manufactured as part of an integrated circuit.

The term passive in this context refers to the fact that PIR devices do not generate or radiate energy for detection purposes.The PIR sensors only detect infrared (IR) radiation emitted by or reflected from objects. They cannot detect or measure “heat”.



A human detection robot is used to detect the humans present around especially during the rescue regimes after a natural calamity such as earthquake, landslide, storms etc. Though the detection is done by rescue teams but it is also important to find the stuck humans within right time. The human detection robot will help at large extent for such rescue operation.

Circuit Principle:

The Human detection robot circuit principle is to detect the humans by using the circuit such as detection sensor ( a PIR sensor). The robot can be handled manually via PC. The wireless technology used here is Radio Frequency(RF) signals. The communication is established using a RF transmitter and a RF receiver.

Circuit Components

  • AT89s51 microcontroller.
  • PIR sensor.
  • 9V battery.
  • Motors
  • L293D IC.
  • PC
  • RF transmitter and receiver.
  • Robot chassis.
  • Max232 IC.

Circuit Design

Circuit design is divided into two parts: transmitter part and a receiver part

Transmitter part

The transmitter part includes a PC, MAX232 IC, DB9 connector, RF transmitter,  The transmitter section is going to be on the robot chassis. The commands for operating the robots are transmitted using PC. PC transmits the data to the RF transmitter through max232. PC logic levels are in the range ± 3v to ± 15V, while the  RF module logic levels are TTL Compatible . Max232 converts the logic levels. This is also called level converter .The T1in pin of the MAX232 is connected to receive pin of the DB9 which further connected to the PC. The output pins are connected to the RF transmitter.

Radio frequency is the wireless technology used to transmit the data .The modules are available at frequencies such as 433.92 MHZ,315MHZ ,868MHZ,915MHZ,2400MHZ. Here the RF modules uses a frequency of  433 MHZ. T1out pin of MAX232 is connected with the DATA pin of RF transmitter. Maximum voltage of 5V is applied to the RF transmitter.

Receiver part

The receiver part includes AT89C51 microcontroller, L293D motor driver IC, RF receiver, motors of the robot,PIR sensor.

The RF receiver module is connected to the port3 of the micro-controller and the Data pins of RF receiver are connected to the receiver pin of the micro-controller. The two VCC pins are shorted and connected to 5V power supply. GND pins are shorted and connected to ground. The receiver module receives the data and transmits it to the micro-controller.

PIR sensor

Passive Infra Red (PIR) sensor plays a primary role in the circuit that is detecting the human being. PIR sensors work on the principle that they every human being emits infra-red radiations of very low wave length. Thus this sensor senses these radiations and outputs a logic high value. This sensor can sense the human within the range of 20 feet. PIR sensor can be connected to the Port1 of the micro controller.It’s operation range is 2.2V – 5V.


L293D is a motor drive IC. This IC is required to drive the motor and also eliminates back EMF generated. This IC internally has H-bridge circuit. The IC has 16 pins out of which 4 input pins drive the motor. Enables are used to enable these input pins. A 5v power is supplied at the 16th pin to operate the IC and 8th pin is applied to 12 Volts power supply.For the reason that voltage L293D can bear is 36V, we can supply a voltage range of 2.4V – 36V to the 8th pin of IC.

Circuit Diagram

PIR Project


1: Burn the code into the micro controller.

2: Arrange the robot chassis.

3: Connect the transmitter and receiver circuits as shown in the circuit diagram.

4: mount the receiver with PIR sensor on the robot.

5: Connect the transmitter to the PC.

6: Enter the character F( As programmed)  in the hyper terminal of the PC.This makes the robot to move in forward direction.Now enter the character B (As programmed) to move the robot in backward direction.Similarly, Enter L and R to move the robot in left and right directions.

Step 6: While the robot is moving if any human detected by the PIR sensor robot stops moving and a buzzer is switched on.


  1. In rescue operations after natural calamities.
  2. War Fields.
  3. In Museums and Jewellery shops to maintain security.


PIR sensor fails to sense humans out of its range.

For more Robotics Projects refer to  Robotics online course.

If you like the project and have queries please write your feedback in the below comments section. It helps us to stay motivated. 🙂

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