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How to build Dark Activated Led or Lamp Flasher

2014-12-12 00:37  
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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.

Circuit Diagram:

Dark Activated Led or Lamp Flasher-Circuit Diagram


R1 = LDRR2 = 100KR3 = 10KR5 = 470RR6 = 47RR4 = 10KC1 = 220uF-25VD1 = 1N4148D2 = LED any type (see notes)Q1 = BC337Q2 = BC337B1 = 3V Battery or 2x1.5V cells in seriesSW1 = SPST Switch


Best results in flashing frequency can be obtained using for C1 a value in the 100 - 1000μF ranges.To drive a filament lamp make the following changes:Use a 2.2 to 3V, 250-300mA bulb in place of the LEDR2 = 10K 1/2W Trimmer CermetR3, R4 = 1K 1/4W ResistorsR6 = 1R 1/4W ResistorC1 = 470 to 1000μF 25V Electrolytic CapacitorIn LED-mode operation the stand-by current consumption is less than 400μA.In Lamp-mode operation the stand-by current consumption is about 3mA.

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