SPOT
THE MISTAKES!
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The circuit above takes 9mA all the time via the middle 1k
resistor and the LED takes 8mA when it is illuminated.
The improved circuit takes 2 microamp when light falls on the
Light Dependent Resistor and the first transistor is turned OFF. This makes it
"disappear" from the circuit and all we have is two 10k resistors connected
between the base and emitter of the PNP transistor and these turn the transistor
OFF. So nothing else in the circuit is taking any current. A huge saving on
current.
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Here is a circuit from the web, from an "engineer" who doesn't understand
circuit design. He claims the "circuit works" and that makes the circuit a good
design.
But if you look at it carefully, the circuit takes the same current when
operating as when it is resting. This is a waste of battery-current. And the
circuit takes DOUBLE the necessary current.
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