How to make a simple security system on a single transistor

You are only at the beginning of the study surprising electronics world and look for simple circuits for practical assembly? Then I want to offer you a very simple watchdog alarm formed on a single transistor. By implementing such a scheme, you can even set it to the input, for example, in the studio and you will always know that you are sent to guests (willing or not). So, let's begin.

We consider the scheme and how it works

But before we proceed to our circuit assembly, let us study it and figure out how it works.

As you can see scheme is extremely simple and it operates as follows: as long as the protective wire has no discontinuities and included in the circuit in the chain "+" supply element - resistor - Guard wire - Negative battery will flow electricity.

And all the current will flow through the protective wire exactly, and this means that the transistor is closed. To it was opened required voltage difference between the emitter and base of 0.5 - 0.7 volts.

And in this state, the circuit can be a very long time (until battery power is exhausted), but as soon as we break a protection wire, at the same moment increases the base voltage to 0.5-0.7 V, the transistor opens and the path of the emitter - collector starts current flows. Now, the chain of the scheme is as follows:

"+" Battery test - buzzer - transistor - minus the battery. And at this time the buzzer just ringing furiously. With the principle of like everything is clear, now let's move on to close assembly.

circuit assembly

In order to raise our scheme will need:

1. Transistor. Suit virtually any, the main thing that it was - the transition N-P-N type.

2. Buzzer (I bought it here). In principle, if it is not, then it can be replaced, for example, low-power LED bulb or flight, designed for 12 volts.

3. Source 12 Volts. I'll use a regulated power supply.

4. Connecting cables, protective wire and a soldering iron.

Since an extremely simple circuit, I just show you the result of the build and test circuits.

conclusion

As you can see, the working scheme and is going to just limit. You can also collect it with your child. Perhaps this work inflame interest in the study of electronics, physics and other sciences with your child. Like the article, then put his finger up, it will show the article to as many people.

If you have interesting ideas, then you are welcome in the comments. Thank you for your attention!