黑暗激活LED或灯闪光威廉希尔官方网站 --Dark-activated

黑暗激活LED或灯闪光威廉希尔官方网站 --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________________220΅F   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 1000΅F 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

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