Article
Passive-Optical Person Detector
responds to changes in ambient lighting
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.
Materials
Gerber file
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PCB
Component list
Resistors:
R1,R6 = 10k?
R2 = 470k?
R3 = 1k?
R4 = 470k?
R5 = 4k?7
P1 = 10k? preset
Capacitors:
C1 = 1µF 16V radial
C2, C4 = 10µF 16V radial
C3,C5,C6 = 100µF 16 V radial
Semiconductors:
D1 = LED, green, low-current
D2 = LED, red, low-current
T1 = BP103
T2 = BC547B
IC1 = LM358P
Miscellaneous:
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
R1,R6 = 10k?
R2 = 470k?
R3 = 1k?
R4 = 470k?
R5 = 4k?7
P1 = 10k? preset
Capacitors:
C1 = 1µF 16V radial
C2, C4 = 10µF 16V radial
C3,C5,C6 = 100µF 16 V radial
Semiconductors:
D1 = LED, green, low-current
D2 = LED, red, low-current
T1 = BP103
T2 = BC547B
IC1 = LM358P
Miscellaneous:
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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