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Passive-Optical Person Detector

responds to changes in ambient lighting

Passive-Optical Person Detector
Ordinary proximity detectors use infrared sensors which respond to the warmth of the human body. But there’s a simpler way: we can use ambient lighting and detect changes in illumination.Any move a person makes causes a change in the ambient lighting. This circuit uses an ordinary phototransistor as its ‘eyes’ to detect these changes. The circuit can detect even the smallest change in illumination: it is not even necessary for a shadow to fall directly on the detector. It is enough if just a part of the sky is occluded. The sensitivity of the sensor can be set using a potentiometer.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor Members can exclusively download these files for free as part of their Membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service. Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

R1,R6 = 10k?
R2 = 470k?
R3 = 1k?
R4 = 470k?
R5 = 4k?7
P1 = 10k? preset
C1 = 1µF 16V radial
C2, C4 = 10µF 16V radial
C3,C5,C6 = 100µF 16 V radial
D1 = LED, green, low-current
D2 = LED, red, low-current
T1 = BP103
T2 = BC547B
IC1 = LM358P
S1 = switch, on/off, 1 contact
BZ1 = 5V DC (active) buzzer
9V PP3 (6LR22) battery with clip-on lead
Enclosure with battery compartment, size 101 x 60 x 26 mm
PCB, available from The PCB Shop
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