Motion Sensor Light Switch

motion sensor light switch is a great way of saving energy shortfall period.  A PIR sensor light switch will automatically detect when someone enters the room or any place where the motion sensor is set. Then, after a few minutes(adjusted by your desires) where no movement has been detected, the lights will then automatically turned off. Although a motion sensor switch is indeed a big and important invention. In fact, you can install a motion sensor light switch much in the same way as you would a single pole light switch. 


SR Components/Part Detail QTY
1 AC/DC Adapter 6v  1
2 Relay 6v 1=amp 1
3 Transistor BC 547/BC548 or equivalent  1
4 Resistor 1K Ohm 1
5 Diode 1N 4007 1
6 PIR sensor 3.3 to 20V DC input 1
7 Bulb  AC bulb or DC bulb can be used 1
8 BCB You can use it without PCB 1

PIR Sensor switch circuit

All living things (human or animals), whose body temperature is more than 0 degrees Centigrade, emit the heat in form of infrared radiation through their body, also called thermal radiations. This Radiated energy is invisible to the human eye. These heat Signals can be detected by using a PIR sensor which is specially designed for such purpose.

This is a motion detector sensor that detects the movement of human beings and triggers its output to High state (low or high). It operates in two modes low and high. The mode is selected by the jumper provided on the rear side of the PIR sensor PCB that is shown on the figure given below. If the sensor with input voltage capability of 12V is not in your reach, use LM 7805/7806 regulator to control the 12v current if you give 12v current directly the sensor may be damaged.


Modes of PIR sensor light switch:

PIR sensor circuit

Normal Mode: When the Passive infrared sensor detects motion it sets the output to High until set time end, independent of the movements during the output HIGH time. This is a One-time triggering mode.

Re-Triggering Mode: When the PIR sensor detects motion, it sets the output to High until a set time becomes Low, but if it detects motion during its output High state 1, it again triggers the timer making it to count from zero.

Sensitivity Adjust

With this potentiometer, you can set the range which you want.

You will have to play a little with this to see what is the appropriate setting for your desired purposes.

Increased sensitivity can be beneficial when using a PIR sensor for long-range, say up to 6 meters or more. 

A decreased sensitivity is good for a very short range to say maximum range or up to 10 feet. Which in turn could miss movements at a longer range?

Delay Time Adjust

The Delay Time indicates how long the PIR sensor will keep the Output High (ON) as detecting motion.

For example, when motion has been detected, you could set this somewhere between a few seconds up to a few minute’s time period.

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