PIR Light Switch. Home Utility Circuit 3

PIR-SENSOR-TOP-VIEWPIR Motion Sensor Modules are now available at low cost and it can be used to make Motion sensor alarms, PIR light switches etc. It requires only a few components and within few minutes, you can make a highly useful gadget for your home. Let us see the details of PIR Module and the circuits.

PIR sensor is an electronic sensor module that measures infrared light radiating from the objects including human beings in its field of view. It is generally called as Motion or Proximity Sensor, Pyroelectric Sensor etc. The sensor in the module detects the infrared radiation emitted from the human body in the form of body heat. Each object with a temperature above absolute Zero (273.15 Degree Celsius or 0 Kelvin) will radiate infrared rays.


PIR Sensor is called as “Passive Infra Red (PIR) sensor because it is not emitting any infrared ray but sensing the Infrared rays passively. PIR has two Pyroelectric sensors inside for comparing the infrared of the surroundings and the infrared rays from the human body. If the difference is too high, it triggers the circuit.
What is inside the PIR Sensor Module?
The PIR module is a fully assembled board with a current sourcing output which can be used to trigger a circuit.


1. Fresnel lens – The PIR sensor is covered externally by a dome shaped plastic cover which acts as a Fresnel lens to concentrate the Infrared to the sensor. It is built of tiny lenses that collect IR from different angles.
2. PIR Sensor – Inside the Fresnel lens cover, there is PIR sensor soldered in the module. It is the chief part of the module to receive the IR.
3. Connector pins – PIR Sensor module has three pins. Vcc that receives 3-12 V DC, Ground and the output pin. PIR sensor module very well works in 3 Volt DC but it handles up to 12 volt DC.


4. Potentiometers – Two Presets are provided to adjust the Sensitivity ( Range ) and the Time delay of the Sensor. The Sensitivity ( Sx ) can be adjusted to few cms to 10 meters. But good sensitivity is available in the midpoint of the preset. Time delay preset (Tx) adjusts the time period by which the output remains high. The Module has a timer circuit so that the output On time can be adjusted between 30 seconds to 3 minutes by turning the pot. When we place the Module down, the Preset close to the IC is Sx and the right one is Tx.


5. Re trigger Jumper – PIR Module has a Jumper to select two modes of operation. The Default setting may be in the “H” position. In the H position, the PIR sensor triggers only when a movement is sensed. In the Non retriggering mode, the Jumper is placed in the “L” position. In this mode, repeated triggering occurs when it detects movements. The “L” positing seems little erratic and output turns high and low repeatedly. So use the “H” position for stable operation of the circuit connected to the Module.

How to Test?
Before using the PIR module, first check its working and adjusts time delay and sensitivity according to your needs. Just connect the Anode of an LED to the output pin (Middle pin) with a 470 Ohms series resistor.


Connect the Cathode of LED to the ground pin. Connect a 9V battery to the Vcc and Gnd pins observing correct polarity (there is Vcc, Gnd and O/P markings near the pins). When you wave hand in front of the lens, LED will turn on. Adjust the presets clock wise for sensitivity and time delay. It is better to keep the wiper of both the presets in the middle position. You get around 2 minutes delay and 6 meters range in this position. After the time delay, LED turns off. The output can be used to trigger a Buzzer or Relay to make a Burglar alarm or Light switch. See circuits.


Simple PIR Burglar Alarm

When a human movement is detected, buzzer beeps for a fixed time ( as adjusted) then goes off. Ideal circuit to monitor Door and Passages.


PIR Light Switch

Very good Surveillance system for Home. When a human movement is detected, Relay triggers to Turn on light.

How to Fix the circuit.
The finished gadget should be placed on the wall above 2-3 meters from the ground level at an angle of 45 degree. This makes a 45 degree field of view to the ground. Direct Sunlight should not fall on the Sensor. It may cause false triggering. Moving tree branches, sudden fluctuations in temperature and sunlight, fluorescent lamps etc may cause false triggering.

Note : It is better to uses a Transformer power supply for error free working of the PIR sensor Module. Use of Transformerless power supply and cheap SMPS power supply may cause erratic working of the Module. The transients in the Mains lines may cause false triggering.

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