A Passive Infrared Sensor (PIR Sensor) is an electronic sensor that measures Infrared Rays which is radiated and detected from objects around its field of view. Passive Infrared Ray Sensors are most time used in PIR- based motion detectors. You can also term a PIR sensor as an electronic sensor that measures Infrared Rays that is the light radiating from a detected objected such as such as human or other objects in its range or surroundings.
A PIR based motion detector is used to detect the movement of object including animals and humans. In a Passive Infrared Sensor, the sensor does not actively take part in the process, that is why it is called Passive. The sensor does not emit IR signals itself, but it passively detects Infrared Rays from objects around or from the human body within its field. The detected radiations are then converted to electrical charge which is proportional to the quantity of radiation detected.
PIR- based motion detector is used in automatically activated lighting in areas such as Garage, and they can also be used in burglar alarms in banks and other institutions even at home.
HOW DOES A PIR WORK
A passive Infrared Ray sensor detects changes in the quantity of Infrared Rays detected around it which varies and its variation is dependent on the characteristic temperature of the person or object that is being detected by the sensor. When for example the person passes by the PIR sensor, the temperature of the sensor rises from room temperature to human body temperature and then back to room temperature. The sensor then converts the detected infrared radiation into a change in its output voltage, this process harnesses detection.
Source
Let us quickly run through a tutorial
using a PIR sensor along with an LDR to turn on or off a light bulb using a Relay.
DESIGNING AN AUTOMATIC GARAGE LIGHT
The things I need to consider before designing the circuit are:
Step 1:
- The bulb should only turn on when the room is dark and when a motion is detected.
- The bulb should turn off after 30 seconds of the object leaving the sensors proximity.
- Most important, we need to place the LDR in a place where it doesn't turn off the bulb as soon as it lights up.
Step 2:
Hardware
For this tutorial we need:
A General Purpose PCB
2 x HC-SR501 PIR Sensor
2 x 1N4148 Small Signal Fast Switching Diodes
1 x 1N4007 High Voltage, High Current Rated Diode to protect the micro-controller from voltage spikes
1 x LDR
1 x 10K Trimmer Potentiometer
2 x 470 Ohms Resistor
1 x 10K Resistor
1 x 1K Resistor
1 x 2N3906 General Purpose PNP Transistor
1 x 2N2222 General Purpose NPN Transistor
1 x 5V Relay
1 x LED to display the status
5 x Terminal Blocks
1 x 220V to 5V Buck Step Down Module
Few Connecting Cables And General Soldering Equipments
Step 3:
Lets first connect the LDR and setup the light detection bit.
As we all know we need to setup a voltage divider to use the LDR in a circuit, so, I am adding this 10K POT and 470ohms resistor to setup the voltage divider bit. By adjusting the resistance of the POT we can adjust the intensity of sunlight at which this circuit will operate.
Now, lets install the PIR sensor. Connect the VCC to +5v and GND to ground. Then connect the 1N4148 diode to the OUT of the sensor. In this circuit, I am installing just one sensor however in the actual project I have used 2 sensors to capture a bit more than 180 degrees. So, to avoid the sensors from back-feeding each other we need to install a diode to the OUT pin of each sensor. If you want to capture motion at 360 degrees you may need 3 to 4 sensor and diode pair to achieve that.
Now that we have the PIR sensor and the LDR in place we need to add the 'AND' functionality. To achieve this I am adding a general purpose PNP transistor. When a motion is detected 'and' when the sunlight is at a certain intensity (adjusted by the POT) current flows out of the transistor.
Next, we need to amplify the current received from the collector of the PNP transistor and turn on and off the LED indicator and the Relay. A general purpose NPN transistor is used to achieve this. That's it all done.
Step 4:
What I Have Made
On my board components are pretty much soldered everywhere, but you may like to have them nicely installed to give it a bit more cleaner look. OK, so lets check out how this works.
Step 5:
Alright, I have placed the board on this table to do a quick test. I haven't hooked up a light bulb to the circuit yet. However, the LED indicator should serve the purpose of this demonstration.
So, now I am going to turn off the light and make the room dark. Let's see if the sensor picks up motion and lights up the LED. Tada, it works.
Now, lets turn on the light of the room and see if the LED indicator turns off or not. Yessss, that works.
OK, finally just want to make sure that the light bulb turns off after 30 seconds of me moving out of the sensors proximity. Boom, and that concludes the project. I can now install it on the ceiling and make my partner happy.
Instead of having 2 to 3 PIR sensors you can use one and install it at the corner of the wall. However, that will require a fair bit of wiring either inside the roof or on the ceiling, which will be way more expensive and tedious than installing 3 sensors an d putting the device in the middle of the room.
You can also swap the Arduino with a NodeMCU board and do a remote data logging to log the time when the sensor detected motion or when the light went on to record when people entered your garage and how long they stayed in there.
Step 6:
Areas of Applications of PIR Sensors
This setup can be used to:
- Automate All Outdoor Lights
- Automate Lights of Basement, Garden or Covered Parking Areas
- Automate Lift Lobby or Common Staircases Lights
- Automate bedside or night lamp
- Create a Smart Home Automation & Security System and more..