DARK DETECTOR Circuit
When
the level of light on the photo-cell decreases, the 555 is
activated. Photo-cells (Photo-resistors) have a wide range of
specifications. Some cells go down to 100R in full sunlight while
others only go down to 1k. Some have a HIGH resistance of between 1M
and others are 10M in total darkness. For this circuit, the LOW
resistance (the resistance in sunlight) is the critical value.
More accurately, the value for a particular level of illumination,
is the critical factor. The sensitivity pot adjusts the level at
which the circuit turns on and allows almost any type of photo-cell
to be used.
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