Hi guys, welcome to electrical projects channel, and in today’s video, I’ll show you how
to build a very simple device that can turn lights on and off automatically, depending
on whether it’s day or night.
For building such device will need one MOSFET transistor 2N7000, light dependent resistor LDR07,
470K resistor, 12Volts relay, and a 12Volts power source.
Also, we’ll need wires.
Here is you can see the schematic.
Well, let’s start building this device.
First, let’s solder 470K resistor and the first lead of light depended resistor LDR07,
then let’s solder them to the gate lead of the MOSFET transistor.
Now let’s solder the second lead of the light dependent resistor
with the source lead of the MOSFET transistor,
and let’s solder to them a black wire.
Now let’s solder drain lead of the transistor to the first coil lead of the relay.
After that, let’s solder the red wire to the resistor and to the second coil lead of the relay.
Now everything is ready, let’s test this device.
For powering I’ll use a 12V power, let’s check the polarity of the power supply,
Okay
now let’s connect everything.
And the last thing is a light bulb.
Let’s connect the light bulb sequentially with normally open contacts of the relay.
And be very careful with mains electricity, because it can kill you, really, be careful.
Make sure that the wires connected correctly and well.
Now let’s plug in,
so far everything seems ok, now let’s cover the light sensor witha black tube.
And…
Oops, something is wrong… here we have a very interesting thing happening,
the light bulb is constantly flickering, instead of just turning on and off.
Do you know what’s wrong? you can pause this video and think for a while,
what do you think is wrong?
Ready for the answer?
Well, here we go: the Light bulb is flickering because we have a feedback between the sensor
and the light bulb, in other words, the light sensor senses the light from the same light
bulb that it's in control of.
And when I cover the sensor, at some point, it’s became too dark and the light bulb
it is turning on, but when the bulb is on, there is too much light so sensor turn the
bulb off, and when the bulb is off its became too dark again so sensor turn on the light
bulb again, and this cycle repeats again and again.
And it means that for the normal work of this device, sensor shouldn’t sense any light
from the bulb that it’s in control of.
Let’s perform one more test, but this time I’ll put the light bulb in the box.
Let’s test it again.
Now it works fine.
Let’s turn off the light in the room.
And at some point, sensor started to sense the light from the light bulb and we have
feedback again, so let's cover the bulb even better,
now Let’s dim the light in the room.
And now it is working just fine.
And that is all for today, I really hope this video was interesting, thanks for watching,
and I’ll see you next time.