About baby pranks or how to protect an apartment door from fire

The simplest scheme to limit the duration of a call.

As you know, children's pranks are not always safe, and can lead to various unpleasant consequences. Even fairly old people, mostly men, recalling their childhood, often say that you could press the button of someone else's call and rush off to the street. And if at the same time you still tie the doorknob to the stair railing or to the neighbor's door! There were plenty of different options for access pranks, all of which could not be listed.

But these pranks were completely harmless in comparison with the "eternal call"! To do this, it was enough to just stick a match in the bell button and, of course, run away. And it did not go somewhere along with the memories. Believe me, such “pranksters” didn’t decrease, as there were no less seductive call buttons.

Normal electromechanical bell It is designed for short-term operation, therefore, a match stuck in a button can, if not removed in time, lead to overheating and even a fire in the call. If the bell hangs on a bare brick wall, then perhaps it will not pass beyond it. But more often under a bell there are wallpapers, a hanger or a closet can be located nearby. It’s not far from the fire.

What is the way out of this situation? The easiest way is to change the call to modern Chinese, which is battery-powered with a radio channel. But the trouble is that these calls are quite expensive, and their reliability leaves much to be desired. Therefore, people are not in a hurry to make such calls, and the habit of the old also affects, makes itself felt.

The way out of this situation is quite simple: you need to somehow limit the ringing time to a few seconds after pressing the button. And then click on it as much as you like - the call will be silent like a fish. In the future, such pranks will stop by themselves, because the expected result was not achieved!

Perhaps the simplest and most reliable scheme for limiting the duration of a call is shown in Figure 1.

Figure 1. Scheme for limiting the duration of the sound of an apartment call.

Device and principle of operation schemes

The scheme is quite simple and contains only six parts. On diodes VD1 ... VD4 assembled rectifier bridge. A capacitor C1 is included in the diagonal of the DC bridge, which sets the duration of the ringing sound. Actually the bell is included in the diagonal of the same bridge, but already for alternating current.

When the button is pressed, capacitor C1 starts charging, the inductive resistance of the ringer coil limits the charge current. At this time, the sound of the call. As soon as the capacitor is charged to the amplitude value of the mains voltage, about + 310V, the sound will stop. To be more precise, the sound will stop a little earlier, namely, when the capacitor is charged up to 2/3 of the capacity, that is, up to approximately 200V. In the future, the charging current drops so much that it is not enough for the sound of the call.

If you now hold the button pressed, then a slight current limited by resistor R1 will pass through the bell and the diode bridge. This current is so small that it can not bring any harm to the call. Therefore, a match stuck in a button is no longer scary. The purpose of the resistor R1 is to quickly discharge the capacitor C1 after releasing the button, and thereby prepare the circuit for the next button press.

Parts and construction

A small number of parts allows you to assemble the entire circuit by mounted mounting directly on the terminals of the capacitor. The capacitance of the capacitor depends on the duration of the call. With the capacity indicated on the diagram, depending on the type of call, the playing time is within 1 ... 2 sec.The electrolytic capacitor must be at a working voltage of at least that indicated on the diagram, better if more, for example, 450V. Diodes can be replaced with KD226G or imported 1N4007 or 1N5408.

The device should be assembled in a housing of suitable sizes, and connected to the gap of any of the two wires suitable for the call. Actually, the body is more needed for decoration and mounting the device on the wall. After all, you must admit that a design hanging on wires does not decorate anything anywhere. In addition, it will certainly attract the attention of a fire inspector.

Boris Aladyshkin, https://env.electricianexp.com/