黑暗激活LED或燈閃光電路--Dark-activated LED or Lamp Flasher

Simple photo-sensitive circuit
3V battery supply

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________________220F 25V Electrolytic Capacitor

D1______________1N4148 75V 150mA Diode
D2_________________LED Any type and color (See Notes)

Q1,Q2____________BC337 45V 800mA NPN Transistors

SW1_______________SPST Switch

B1__________________3V (Two 1.5V AA or AAA cells in series, etc.)

Circuit operation:

This circuit adopts the rather unusual Bowes/White emitter coupled multivibrator circuit. The oscillation frequency is about 1Hz and is set by C1 value. The LED starts flashing when the photo resistor is scarcely illuminated. The onset of flashing can be set by trimming R2.

Notes:

Best results in flashing frequency can be obtained using for C1 a value in the 100 to 1000F range.

To drive a filament lamp the following changes must be made:

Use a 2.2 to 3V, 250-300mA lamp in place of the LED

R2 = 10K 1/2W Trimmer Cermet

R3, R4 = 1K 1/4W Resistors

R6 = 1R 1/4W Resistor

C1 = 470 to 1000F 25V Electrolytic Capacitor
In LED-mode operation the stand-by current consumption is less than 400A.

In Lamp-mode operation the stand-by current consumption is about 3mA.