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How to Make DIY Security Alarm Device with a Reset Button | DIY Project

How to Make DIY Security Alarm Device with a Reset Button | DIY Project


Hi, guys, welcome to electrical projects channel,
and today, in my laboratory I am going to build a security alarm device with a reset
button. This device is relatively simple and doesn’t
require any expensive components. Well, for building such alarm device we will
need: 4 transistors BC547B, six 10 Kiloohms resistors, and two 1 Kiloohms resistors, and
also we’ll need a small button, for reset, and an active 12V buzzer. And for triggering this alarm, I will use
a reed switch and a magnet. Also, we’ll need wires. Now we are ready to start soldering. but first let’s look at the schematic, and
at first, for some of you, it may seem complicated, but actually, it is not, especially when you
understand what each part of this circuit does. In the center, you can see a regular flip-flop
circuit, this part of the circuit has some memory, and maybe word “memory” is too
strong in our case, because it only remembers one bit of the information, one or zero, in
our case it will remember whether the alarm was triggered or not. And I’ll show you how it works later in
this video. On the right side you can see Transistor Q4
it Controls the active buzzer, and works like a buffer, between flip-flop circuit and the
load. Transistor Q1 on the left part will trigger
the flip-flop circuit, I’ll explain why we need it a little bit later. To make soldering and troubleshooting a little
easier, at first I am going to build only a part of this circuit and test it, and then
we’ll go further. I will not use any PCB
board, so it will be easier for you to see how everything connected. Well, First I am going to connect and solder
a black wire to emitter leads of transistor Q2 and Q3, Then, let’s connect two 10 Kiloohms resistors, according to the circuit, so each resistor
should be connected from collector lead of the first transistor to the base lead of the
second transistor. And Now let’s solder 1 Kiloohms resistors
to collector leads of the transistor Q2 and Q3. Also let’s solder 10 Kiloohms resistor between
the collector lead of transistor Q3, and the base lead of transistor Q4. Emitter lead of the transistor Q4 should be
connected to the negative wire, which in our Let’s solder everything. And now we can solder the buzzer. Let’s solder the minus lead of the buzzer
to the collector lead of the transistor Q4. And this part of the circuit is almost ready. Now let’s solder the red wire to the plus
lead of the buzzer, and to the 1Kiloohms resistors. And before we go any further, let’s test
this part of the circuit. For the testing, we need to connect this circuit
to a power source. I’ll use a 12V battery. But it is not all, in order to test this device
I’ll connect a 10 Kiloohms resistor to this yellow wire, and connect this wire to the
plus lead of the battery. Now let’s test it. Now when I touch the base lead of the transistor
Q2 it activates the buzzer, and when I touch the base lead of the transistor Q3 it turns
the buzzer off. As you can see everything works fine, which
means that we’ve soldered everything correctly. Now let’s solder the button to the wires. After that let’s solder the first wire to
the base lead of transistor Q3, and let’s and let’s solder the second wire to 10 Kiloohms resistor. After that 10 Kiloohms resistor should be
soldered to the positive red wire. And Now you can test this circuit again with
a wire and 10 Kiloohms resistor, but it is not necessary. As you can see, you can already trigger this
alarm and reset it with a button. And you may wonder why we need one more transistor. And it all because of how reed switch works. Let me show you. As you can see without the magnet the reed
switch doesn’t conduct any electricity, and only starts to conduct electricity when
I bring the magnet to it. And if I just install this switch with a magnet
on a door, it will trigger the alarm when I close the door, and not when I open it,
which is not what I need, and that is why we need one more transistor. So, let’s solder it and I’ll show how
it works with one more additional transistor. Let’s solder the emitter lead of the transistor
Q1 to the base lead of the transistor Q2. Then let’s solder 10 Kiloohms resistor between
the collector lead of the transistor Q1 and the positive wire. And let’s connect one more 10 Kiloohms resistor
but this time between the base lead of the transistor Q1 and the positive wire, Now let’s connect two wires that will go
from this device to the reed switch. Let’s solder the first wire to the base lead of the transistor Q1 and let’s solder the second wire to the minus And this device is ready, let’s test it again. Now if I disconnect these wires it will trigger
the alarm. And even if I connect the wires together again,
it will not turn the buzzer off. You need to reset the alarm with this button. Let’s see how it works in real life. I’ve installed the reed switch on this door,
and connected to our device, let’s see how it works. Everything works. And that is all for today, I hope this video
was interesting. Thanks for watching, and see next time!


Reader Comments

  1. This is just what i am looking for, nice job. The only problem is that i want more noise. i wanted 30 whats so the theef gos running like hell. Haw do i do that? Or is it possible. Thx for info man

  2. I have made this alarm but my alarm is not reset by push button …… instead of push button what can i use ?
    Or Can u explain this circuit theoretically how it works ?

  3. can i bulid basic flip flop circuit without resistor? (use transistor (bc547B) , led only (for fun)) . i try to build a circuit without resistor but two led switch on .

  4. Hi
    I tried your circuit its ok but
    after every 4 minutes it automatically on's the buzzer
    solution please

  5. Hi. Have done your circuit and it works well. The only thing is the buzzer (12V) have not enough power to buzz loud. If I connect only the buzzer with battery, everything is fine (loud)( but when it turn on within the circuit, the sound level is too low. Any suggestion?

  6. Hi can u help me pls for my project, if i want to change the reset button into a bluetooth reset directly alarm to my cellphone, how can i connect the the bluetooth reciever??? Pls help

  7. sir its nice project but i have question if door open for prolong time like 1 hour and during this time if i reset alarm i want buzzer stop buzzin how can is achive? if yes how please reply me?

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