LED indication of apartment bell operation modes. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Lighting

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Room calls are an integral part of our life. They are not equipped except that country houses, and even then not all. Traditionally, such a notification system about the arrival of guests consists of an electric bell in the apartment and a button on the front door. But families with small children suffer from such "primitivism". Often the guests arrive exactly at the time when the child was put to bed. A loud call can wake him up. And if someone mixed up the apartments and persistently calls at night ... It's not pleasant enough. To avoid such troubles, the radio amateur must solve two problems: provide the ability to turn off the sound signal and provide a light indication of this mode and the arrival of a guest.

Recently, many such designs - extremely simple and without the use of scarce parts - have been published in amateur radio magazines. The proposed one differs in that it gives a signal about pressing the button of the off call not only to the owner of the apartment, but also to the guest. Indeed, if the guest does not hear the signal when pressing the bell button, then, believing that the bell is faulty, he will most likely begin to "drum" on the door. But if there is a light indication of pressing, he will consider that the call is far inside the apartment and is not audible only for this reason.

Fig. 1

In the alarm system, assembled according to the one shown in Fig. 1 scheme, two two-color LEDs HL1 and HL2 are used with crystals of different glow colors connected in anti-parallel. One of the LEDs is placed in the housing of the SB1 button installed outside the apartment door, and the second - inside the apartment next to the SA1 switch. When the SB1 switch is closed, the electromagnetic bell HA1 works as usual: it rings when the SB1 button is pressed. shunting by diodes VD5 and VD6 of capacitors C1 and C2, each of them is charged only in "its" half-cycle of the mains alternating voltage. Although the capacitance of the capacitors is the same, their charging rate turns out to be different, since in the positive half-cycle the current flows through the diodes VD2, VD3, VD6 and resistors R1, R2, and in the negative half-cycle through the diodes VD1, VD4, VD5 and the resistor R3. This leads to the fact that the capacitor C2 charges faster, and the total voltage across the two capacitors is applied minus to the symmetrical dinistor VS1 and plus to the resistor R4. As soon as it reaches approximately 30 V, the dinistor opens and the capacitors are discharged through the "green" LED crystals HL1 and HL2, after which the dinistor closes and the process repeats. The amplitude of the current pulses through the LEDs is limited by resistor R4.

When the switch is open, the charging circuit for capacitor C2 is also open, and it stops charging. The total voltage on the capacitors C1 and C2 changes polarity, and after opening the dinistor VS1, the current flows through the "red" LED crystals. In this situation, when you press the SB1 button, the bell winding of a relatively low resistance (2 ... 3 kOhm) forms a voltage divider with resistor R1 of a much higher resistance. It decreases so much that it becomes insufficient both for the sound of the call and for opening the VS1 dynistor. The LED flashes stop. This signals to the host that the guest has arrived, and to him that the signal has been received.

If the ratings of the elements correspond to those indicated in the diagram, the frequency of green flashes (the bell is on) is about 5 Hz, and the red one (the bell is off) is about 2 Hz.

When analyzing the considered circuit, it suggests replacing the assembly of resistors R2, R3 and diodes VD3, VD4 with one resistor with a resistance of 33 kOhm. In this case, the value of the resistor R1 must be reduced to 16 kOhm. This option was tested, but it turned out that when the SA1 switch is open and the SB1 button is pressed, the voltage applied to the HA1 bell does not decrease sufficiently and the “off” bell signals, although weakened, are still audible.

Two-color LEDs L-57EGW can be replaced, for example, KIPD45A-M - KIPD45V-M and others with back-to-back crystals and two outputs. If these could not be found, you can also use the more common two-color LEDs with three leads, one of which is a common cathode, and the other two are anodes of crystals of different glow colors, for example, L-59EGW. They are switched on instead of two-output ones according to the scheme shown in fig. 2.

Fig. 2

You can also use a regular single-color LED by turning it on through a diode bridge (Fig. 3). In this case, the bell operation mode (on-off) will be indicated only by a different blinking frequency of the LED.

Ris.3

The wires leading to the LED installed outside the apartment usually have to be made quite long. They are easy to break, including deliberately out of hooligan motives. If this happens, the discharge circuit of capacitors C1 and C2 will be broken, and they will be charged to a voltage close to the mains amplitude (more than 300 V). Capacitors that are not designed for such a voltage will break through and even collapse.

If it is not possible to prevent such a development of events by installing oxide capacitors for a voltage of at least 350 V (for example, the dimensions of the device are limited), then it is recommended to connect a pair of series-connected dinistors similar to VS1 between the positive terminals of capacitors C2 and C1.

Author: E. Yakovlev, Uzhgorod, Ukraine; Publication: radioradar.net

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