Passive Infrared Sensor

HC-SR505 Mini PIR Motion Sensor is based on infrared technology and it can automatic control by itself with high sensitivity and high reliability.


Because of the minimum size and low-power operation mode, it widely used in various automatic electronic equipment, especially battery-powered automatic products.


Working Principle:

The PIR sensor itself has two slots in it, each slot is made of a special material that is sensitive to IR. When the sensor is idle, both slots detect the same amount of IR, the ambient amount radiated from the room or walls or outdoors. When a warm body like a human or animal passes by, it first intercepts one half of the PIR sensor, which causes a positive differential change between the two halves. When the warm body leaves the sensing area, the reverse happens, whereby the sensor generates a negative differential change. These change pulses are what is detected.


Types of PIR Sensors:




Additional info about types:

There is no control on time delay in HC-SR505 that is available in HC-SR501.


Features :

1.Automatic Control

2.Minimum size

3.Repeatable Trigger

4.Wide range of operating voltage


6.Output high signal


Specification :

1.Operating voltage range: DC4.5-20V

2.Quiescent Current: <60uA

3.Trigger: reusable trigger (default)

4.Delay Time: The default 8S + -30%

5Board Dimensions: 10 * 23mm

6.Induction angle: <100 degrees cone angle

7.Sensing distance: 3 meters

8.Working temperature: -20 to +80 degrees

9Sensor Lens Dimensions: Diameter: 10mm


Link to datasheet:


  1. Always take sensor from sides only.
  2. Read the specifications before using any sensor.


  1. Do not make wrong connections like, power supply to gnd. It may damage the sensor.
  2. Do not touch circuit elements, the static energy from your hands can damage the sensor.

Storing Instructions:

It must be stored in thermocol or in a box with care, so that static energy does not damage the components of sensor.



  1. It can be used in environment having irregular heat cycles.
  2. It detects motion in light and dark conditions reliably in indoors.
  3. It has wide range of operating voltage.
  4. It is small in size.


  1. Radio frequency in microwave range do not penetrate metal objects (active type).
  2. It has sensing distance is not more than 3 meters.
  3. Passive sensor type works in LOS (Line of Sight) and does not work in non-LOS regions. 
  4. Any kind of moving object can trigger the PIR sensor type. 



Interfacing with Arduino:

Arduino Code:

void setup() {





void loop() {

if(digitalRead(7)==HIGH) {

Serial.println(“Somebody is here.”);



else {








  1. Body induction lamps.
  2. Body sensors toys.
  3. Security Products.
  4. Industrial automation and control.



Q1. What is the meaning of ‘passive’ in its name?

Ans. ‘Passive’ refers that it does not emit any types of heat radiations, only detects the heat radiations from surroundings.


Q2. Which material is used to make the covering of sensor?

Ans. It is Fresnel lens used for focusing, energy collection, collimation and diffusion.  

Q3.Does clothing affect sensor performance?
Ans. The amount and color of clothing can make a small difference in Sensor performance. Because clothing affects the amount of IR radiation emitted by the human body, it changes the differential between human body and ambient temperatures. The effect of clothing, however, is minor compared to the influence of ambient temperature.

Q4.What is the maximum sensing distance—and can it be adjusted? 
Ans. The best IR Sensors have a nominal sensing distance that can range from 2 to 12 meters, depending on the model. This distance specification does not necessarily represent the farthest distance the Sensor can detect. Instead, it is the maximum distance at which sensing is guaranteed. IR motion Sensors do not have an adjustable distance setting, but you can limit the Sensor’s detection range by mounting it at an angle that blocks its field of view.