One week we open our electronics workshop to share a lesson, this time very focused on practice . The proposal is to learn to design and manufacture a central alarm itself. A montage can be done with easy to find ingredients and detailed instructions for anyone to get to work. Who gets underway?
We start by explaining the utilities and features of the proposed circuit. In figure 1 you can see the electronic circuit diagram, which as shown is quite simple. The power thereof may be by a 9V battery or by a feeder connected to 220v .
The circuit consists of two contacts , one normally closed and one normally open, with any of which can produce the shot of this small central alarm, and therefore the siren connected to it. In our circuit triggering the alarm simulate it using buttons , replaced the “mermaid” by a LED diode that lit indicates that the alarm has been triggered.
Having explained the general operation of the plant, we will describe the electronic circuit operation .
The first component to be described is marked in the schema as the SCR1 , which is a component of three pins known as ” thyristor ” although its correct name is SCR (Silicon-Rectify-Control), ie a rectifier silicon controlled . This component in idle state behaves like an open circuit, as no drive pins between its anode and cathode which is any polarity applied thereto.
When a current is injected pin control marked thyristor as G (Gate) gate, the thyristor is “hit”, that is rendered conductive, remaining in this state indefinitely, even when the gate current is suppressed. At this time, the SCR will remain on until sign- off circuit power, then this is a latching alarm and is not timed, staying on until us Let’s turn.
How to implement this trigger pulse is through resistor R1 , closing switch S1 or through the resistor R2 , opening the switch S2, which remains connected to the rest mass. The diode D1 prevents the alarm is triggered by the closure of S1, the current is derived to ground by the switch S2, which would prevent the firing of SCR1. The capacitor C1 prevents rebounding contacts or any noise that reaches the firing pin can produce false alarms. Thyristor SCR1 when triggered the connects the diode LED LD1 , which has limited current through the resistor R3 .
In parallel with this diode and resistance, we can connect any device that is fed to 9V, and this will become operational when triggered the alarm. You see this circuit is also an open system , in which we propose that apliquéis all your ideas and improvements, which we are sure we will be many.
We suggest a few:
For example, it can be connected as alarm one small siren v 9 or 12 or any type of buzzer of that we have at home. The trigger buttons can be replaced by magnetic contacts , or relay contacts a passive infrared detector. A good idea would be to replace the buttons for a contact mercury or vibration, and ride around the circuit in a box of our vehicle or motorcycle, feeding all for the battery 12. In this case, just a slight bump or movement to produce the alarm. Normally contacts open or closed, they can form loops in parallel and series respectively, thereby forming peripheral circuit protection.
As you can see is very simple perfect and practical experience with this circuit , which poses no risk or danger of malfunction. To assemble the circuit, and as in all previous assemblies, you can use the breadboard plates , or any of the lines or points if you decide to mount a permanent circuit.
Who are encouraged? We love to see your own alarm central.
If you need components you can find them on our website , as well as an electronics course with which you can learn by practicing topics and projects similar to this.