The Circuit Diagram of Simple Low-Voltage Photo Sensitive Dark Detector

November 26th, 2009

This circuit using photo-sensitive resistor as a sensor and LED that will starts flashing when the photo resistor is scarcely illuminated, very simple circuit operate with 3V batteries. The oscillation frequency is about 1Hz and set by C1 value. The onset of flashing can be set by trimming R2. The best result in flashing frequency can be obtained using C1 with value in the 100 to 100uF range.

Parts:

R1———————————-photo resistor (any type)

R2———————————-100K 1/2W trimmer cermet

R3,R4——————————10K 1/4W Resistors

R5———————————-470R 1/4W resistor

R6———————————-47R 1/4W resistor

C1———————————-220uF 25V Electrolytic capacitor

D1———————————-1N4148 75V 150mA Diode

D2———————————-LED

Q1,Q2—————————–BC337 45V 800mA NPN transistors

SW1——————————–SPST switch

B1———————————-3V batteries

In LED mode operation, the standby current consumptions are less than 400uA. You can also use a filament lamp to replace the LED. Use a 2.2 to 3V, 250 to 300mA bulb in place the LED. Replace R2 with 10K 1/2W trimmer cermet, R3 and R4 with 1K 1/4W resistor, R6 with 1R 1/4W resistor, C1 with 470 to 1000uF 25V electrolytic capacitor. In lamp-mode operation, the stand-by current consumption about 3mA.

source : www.redcircuits.net
photo-sesitive-dark-detector

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