Hi, guys welcome to electrical projects channel, and in today’s video, I’ll show you how
to build very simple security alarm system that uses lasers.
You’ve probably have seen such security devices many times in the different movies,
And that is what I am going to build today.
Let’s have a look at what we components we need for making such alarm system.
The main component, of course, is a cheap laser pointer.
Also, we’ll need two MOSFET transistors 2N7000, an active buzzer, a Light dependent
resistor LDR07, a button for reset, an LED for indication and two resistors, one of which
is 1K Ohms resistor and the second 470 Ohms.
Also we'll need wires.
For the powering, I’ll use a 5V power supply.
Let’s start making this device.
On the left side, you can see the schematic, as you can see it is really simple.
Well, let’s start building.
First, let’s disassemble this laser pointer
and let’s solder two wires that will power the laser.
Let solder the negative wire to the resistor,
like this…
and the second wire I will connect to the housing of this laser pointer.
Now let’s check that this laser still works.
Let’s connect the power supply and do a test.
Good sign, the laser survived my soldering which means that we can continue building
our security system.
Ok let’s continue, First, I am going to
solder two wires to this button.
Now let’s solder a 1k resistor between the gate lead and the source lead of the MOSFET.
Now let’s connect the button in parallel to the Light dependent resistor.
Now let’s solder the button with the light dependent resistor to the gate lead of the MOSFET.
Now let’s connect the negative wire from the laser to the drain lead of the MOSFET,
And let’s connect the positive wire from the laser to the button with the light dependent resistor,
Okey,
Now let’s connect a black and a red wire that will be connected to power supply later.
We need to connect the black wire to the source lead of the MOSFET.
And the red wire we need to connect to the yellow wire that powers the laser
Now let’s do a quick test.
To do a test let’s connect what we’ve built to the power source.
Now when you press the button the laser turns on, and when you release the button the laser
turns off.
Well, nothing special here, but It becomes much more interesting when I point the laser
at the light dependent resistor.
Now when I press the button the laser stays on, it stays on until I block the light.
Pretty cool, isn’t it?
As you can see this part of the circuit works well and when I block the light from laser
it triggers our security system, but so far we don’t have any buzzer to indicate that.
So let’s build the remaining part of the circuit.
First I am going to solder the LED and 470 Ohms resistor sequentially.
Now let’s connect the LED and resistor to the buzzer.
Now let’s solder the drain lead of the transistor Q2 to the minus lead of the buzzer and to
the cathode lead of the LED.
Ok, now let’s solder the plus lead of the buzzer to the positive red wire.
Now let solder the source lead of the transistor Q2 to the negative black wire.
And last what we need to solder is the gate lead of the transistor Q2 to the Drain lead
of the transistor Q1.
Ok, this device is ready to let’s test it.
Let’s connect everything to the power supply.
and let’s plugin.
Ok, now let’s press the button and let’s point the laser at the light dependent resistor.
Ok, let’s see how it works.
As you can see it works.
Pretty cool.
Now, I’ve pointed the laser at a mirror and the mirror reflects the light from the
laser right at the light dependent resistor.
Let’s see how it works this time.
And that is all for today, I hope this video was interesting, is so then like it.
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And Thanks for watching!