PIR Sensor Module is one of the new introductions in electronics which is a highly useful device to switch on lights when it detects a human movement. It turns on the lights from 30 seconds to 3 minutes depending on the preset adjustments. Its range can be as high as ten meters which can also be adjusted. The module gives a high output when it detects the human movement. This high output can be used to drive a relay through a switching transistor. Let us see the details of PIR sensor module.
How it works?
All warm blooded animals especially human beings emit Passive Infrared ( PIR) from the body heat. The sensor module has a PIR sensor. Inside the PIR sensor, there are two Pyroelectric sensors. One is Reference sensor and the other is Trigger sensor. The Reference sensor remains active by considering the background temperature as reference. When a human movement occurs, it causes minute changes in the atmospheric temperature due to PIR from human body. This change is sensed by the trigger sensor and a corresponding output voltage appears.
The PIR sensor Module has PIR sensor, Signal amplifier circuit and a Timer circuit. The weak output signal from the PIR sensor is amplified by the signal amplifier and triggers the timer circuit. So the output from the module turns high based on the setting of the delay preset.
How to connect?
PIR Sensor module has three pins for connections. Vcc pin, Ground and Output. So a three pin connector can be used to connect the module with the relay driver circuit.
PIR sensor has power regulation and it works between 5 volts and 12 volts. Output gives 3.3 volts which is sufficient to drive the switching transistor. Use a Transformer based power supply or battery to avoid false triggering.
There are three adjustments in PIR sensor module
Delay – It is a miniature trim pot to set the time delay of output from 30 seconds to 3 minutes. Turn the preset clock wise to increase the time delay.
Sensitivity – The preset can be turned clock wise to increase sensitivity from 30 c.m to 10 meters.
Trigger – There is a Jumper arrangement to select single trigger of multiple trigger. In single trigger mode, the sensor triggers with a single movement. In multiple trigger mode, the sensor turns active only when there is multiple movements.
Night active setting.
There is a provision for adding an LDR in the module so it becomes active only after sunset.
The PIR sensor module should be fitted 2-3 meters above the ground level at an angle of 45 degree because its sensing area is in a cone of 45 degree angle. It should be fixed in an area free from direct sunlight, moisture etc. There should be a background like wall to get more accuracy of sensing. Initially at power on, the sensor triggers and switch on lights. After the set period, output goes low and light turns off. Now the sensor is idle to sense further triggering. It takes around 10 minutes for stabilizing the sensor.
False Triggering – Sometimes the Sensor shows false triggering. Shadow of trees, sudden changes in sunlight, power fluctuations, Fluorescent lamps, Fly, animals like Cats, Dogs etc can cause false triggering. If a light is used with the relay, it will not cause nuisance and if alarm is connected, it may create some nuisance.
The PIR sensor is mainly imported from China and Taiwan etc. Now it is a low cost one and its rate will be between Rs. 70 and Rs.200 based on the quality.