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Circuits > Motor, light and power control > Dark-activated LED or Lamp Flasher
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________________220µF 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 1000µF 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 1000µF 25V Electrolytic Capacitor
- In LED-mode operation the stand-by current consumption is less than 400µA.
- In Lamp-mode operation the stand-by current consumption is about 3mA.
Title: Dark-activated LED or Lamp Flasher
Source: www.redcircuits.com
Published on: 2005-02-03
Reads: 500
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