Dark activated light is an automatic device which can
be used to start the light as soon as it becomes dark in the room. In this project,
I will
glow a LED. But you can use a relay instead of the LED. You can use this
project to control different equipment by simply replacing the LED by a relay.
Apparatus:
- · LED
- · Connecting wires
- · Button cell
- · Button cell holder
- · LDR(light dependent resistor)
- · Transistor(2N3904)
- · 1 Resistor(330 ohm)
- · 1 Resistor (1 Kohm)
- · Circuit board
Circuit Diagram:
Lets see its working:
When it is bright outside, the LDR is exposed to
light. As a result the resistance of the LDR becomes very low .The current
which passes through the 100K will pass in parallel of LDR and the base of
transistor. But the resistance of the LDR is very low so a large portion of
current will pass through it and a small amount of current will pass through
the base. The voltage across the base will be low. As a result transistor will
act as an open switch because the collector base junction will not be forward biased.
Thus the LED will not glow.
But when it is dark outside the LDR will be having a
resistance of 2M and the resistance of the base junction is only 400K thus the
majority of Current will pass through the base. The collector and base junction
will be forward biased. This the LED will glow.
Pic:
Modifications u can make:
You can use a relay instead of the LED. When enough
current will pass through the Relay it will activate the switch and thus the
relay can be connect in series with a lamp to control it.
There are many other Complicated circuit using which
you can make this project but this is
the simplest one .If you have any doubts you can ask in the comments, I will reply
J
This is the Video of its working:
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