1
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theory of operation: the ne555 chip is biased in such a way that the output (pin #3) goes low when pins #6 and #2 are brought higher than 2/3rds of the voltage between pins #1 and #8.
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2
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theory of operation: conversely, the output (pin #3) goes high when the voltage at pins #6 and #2 are brought lower than 1/3rds of the voltage between pins #1 and #8.
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3
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the light-sensitive resistor (often called light-dependent resistor, or "ldr") has a very low resistance when exposed to bright light, and a very high resistance when in the dark.
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4
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under bright ambient conditions, the output of the ne555 is low, and is high dark ambient conditions.
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5
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the light-emitting diode provides the light source required by the "ldr".
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