Proximity Detector Alarm

Here’s circuit that react in presence of any conductor object including humans.
This circuit does not detect object movement but can act as a proximity sensor!
Sensitivity is adjustable with P1 (located at sender PCB)
which will be located at a great distance from the rest of the presence detector circuit.
This is infrared based proximity detector which include infrared emiter and depending ambient light
infrared receiver. This infrared receiver works only in night. A light dependent photo-diode (BPW24R)
blocks the 555 oscillator with negative potential on his pin 4.
One activated alarm, will stay in activated position for the next 3 minutes.
The burglar do not have cognition when the alarm is activate. Time delay of 13 seconds is provided by
another 555, before the intruder leave the monitoring area.
Optimal detection range for this proximity sensor is 1.5 to 3m.
Resonance frequency of oscillator is 38 KHz. TSOP 1738 is integer infrared receiver.
Relay which is driven by serial transistor is use to switch the light in protected area.
No alarm, no sound. Only turned light in the house simulate that household is just wake-up.

This project is published in Emiter 9/2007
Follow the link:

author: Primarius D-r Petar Avramovski, MD


  1. MYLA LOVA KIRANVARMA August 24, 2012 1:10 pm 

    Really nice! but the range of the IR is two small. You can achieve the range by increasing the voltage.
    similar article can be found in

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