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This circuit is based on a passive infrared (PIR) sensor, which automatically switches on a device when someone comes close to it. It can be used for detection of theft or an unauthorised person entering a restricted area or building. It can also turn on lights when someone approaches the area where it is installed. Applications of this circuit include security systems, corridor lights and bathroom lights, among others.

Fig. 1: Circuit diagram of the motion detector

Circuit and working

4B9_TestThe circuit diagram of the motion detector using NE555 timer is shown in Fig. 1. It is built around 230V AC primary to 9V, 300mA secondary transformer X1, bridge rectifier DB107 (BR1), 6V voltage regulator 7806 (IC1), timer NE555 (IC2) and a few other components.

The 230V AC mains is stepped down to 9V, 300mA through step-down transformer X1. Secondary output of X1 goes to bridge rectifier BR1. Capacitor C1 filters the ripples and the rectified output is given to regulator 7806 (IC1). IC1 provides 6V regulated DC output to operate the circuit. LED1 is used as a power-on indicator.

63A_pathsIC2 is configured in monostable mode. Time period of IC2 is based on resistor R4 and capacitor C3, which is around ten minutes in this case. By changing resistor R4 and capacitor C3 you can change the time period of IC2.

Output pin 3 of IC2 is connected to the base of relay driver transistor T2. Contacts of relay RL1 are connected to the load, which could be a CFL or a bulb connected across CON2.

The PIR sensor is a pyroelectric device developed for detection of human body infrared radiations. It has a single output that goes high when a valid motion is detected. That is, the load is switched on whenever the PIR module senses a body in motion nearby.

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22 COMMENTS

  1. ITS Not working, IC and voltage regulator are over heated.When initially power on relay is activated and not sensing the circuit

  2. Sir please help
    It’s not working .When initially power ON the relay is activated and not sensing .I remove the sensor but relay not OFF
    The circuit not reset

    • The relay should not get energised without PIR sensor input. First check proper connections in the circuit including correct polarities and orientations of various active components. If connections are ok, make sure that voltage at pin 2 of NE555 is high when sensor is not connected and low when sensor is connected and motion is detected.

  3. Note that when power is switched on, the relay will energise for around ten minutes. If relay is not de-engerise even after ten minutes, first check whether transistor BC547 is faulty or connected in wrong position. If it is ok, next check IC2.

    • The relay should not get energised without PIR sensor input. First check proper connections in the circuit including correct polarities and orientations of various active components. If connections are ok, make sure that voltage at pin 2 of NE555 is high when sensor is not connected and low when sensor is connected.

  4. sir
    i want to make a muscal buzer with the use of bt66 transister and 27mm 3-pin piezo,
    i have been try many time but i’m not 100% succes.
    so please help me

  5. Why you did’t use a transistor to switch relay instead of using 555 ic. As there are no time events, this circuit can be made by only switching the transistor when pir sensor pin give output.

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