Under normal conditions, transistor T1 is cut off and collector output is high around 6V. When motion is sensed, output pin (OUT) of the sensor becomes high, making transistor T1 to conduct for a few seconds, and voltage at its collector goes low momentarily. This low signal triggers IC2. Output pin 3 of IC2 goes high for around ten minutes, energising relay RL1 through transistor T2, turning on the load for ten minutes.

In brief, when someone comes in front of the PIR module, its output triggers IC2 to turn on the load. Thereafter it is disabled automatically.

Fig. 2: Actual-size PCB of the motion detector
Fig. 3: Component layout of the PCB

Download PCB and Component Layout PDFs: click here

Construction and testing
An actual-size, single-side PCB for the motion detector using NE555 timer is shown in Fig. 2 and its component layout in Fig. 3. Enclose the PCB in a box and install it at a suitable location. Connect the PIR module across CON1.

Connect transformer X1 to 230V AC mains. Verify various test point voltages as given in the table to ensure proper working before using the circuit.


Kumar Abhisekh is a third-year student of B.Tech (electronics and communication) at SETGOI, Institute of Engineering & Industrial Technology, West Bengal

23 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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