Bell with remote control. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Bell with remote control. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Calls and audio simulators

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The call offered to the attention of readers has a galvanic isolation from the network, and a safe voltage is supplied to the call button. It can be used, for example, in garden and summer cottages, as well as in other cases when the wire connecting the button and the bell is accessible to touch. At 220 V, which is typical for a conventional bell control circuit, this can be dangerous to others.

Schematic diagram of the bell ringer is shown in fig. 1. It consists of a tone signal generator, made on a specialized chip KR1008VZH4, and a power supply. The generator is assembled according to a scheme that does not differ from the typical one [1]. Its work is controlled by the transistor VT5. When the contacts of the call button SB1 are open, the transistor VT5 is opened by the base current flowing through the resistors R7, R8, and a low level signal is present on its collector. When the contacts of the call button are closed, the transistor VT5 closes and a high level signal is sent to pins 5 and 11 of the DD1 chip. The generator starts, and a tone signal appears at the output of the microcircuit (pin 7, 6). It enters the BF1 piezoceramic emitter, which emits a melodic ringing.

(click to enlarge)

When the SB1 button is pressed, the HL1 LED mounted in its housing goes out.

The main unit of the power supply is a voltage converter [2], assembled on transistors VT1 - VT4 and transformer T1.

Along with such advantages as simplicity and reliability, magnetotransistor generators with a saturable transformer also have a significant drawback. The fact is that the transition of the transistor of one of the arms of the generator from the open state to the closed state is accompanied by an uncontrolled increase in its collector current. The presence of such powerful current pulses forces the use of transistors with an allowable collector current that is several times higher than the rated operating current, which, in turn, leads to poor use of transistors in terms of current and a decrease in the efficiency of the entire device. Short pulses of the collector current are also a source of interference. To eliminate this shortcoming, current-limiting transistors VT1, VT2 with current sensors R3, R4 are installed in the converter. Resistor R6 limits the base current of the key transistors, and R5 creates the bias current necessary to reliably start the converter.

The voltage converter is powered by a rectifier, which includes a quenching capacitor C1, a resistor R1 limiting its charging current, a bridge rectifier VD1, zener diodes VD2, VD3 with a total stabilization voltage of 30 V and capacitors C2, C3, smoothing the ripple of the rectified voltage [3].

The voltage from the secondary winding of the transformer T1 of the converter is fed to a full-wave rectifier on diodes VD4, VD5, filtered by capacitors C4, C5 and used to power the DD1 microcircuit. The HL2 LED connected to the rectifier output indicates the device is turned on.

All elements of the call, with the exception of the SB1 button and the HL1 LED, are placed on a printed circuit board made of one-sided foil fiberglass 1,5 mm thick. Its drawing is shown in Fig. 2. The board is installed in a plastic case, which is placed indoors. During installation, MLT resistors were used (C2-23 and the like can be used), C1 is made up of five capacitors K73-17 0,1 μm x 400 V, K52-1b (C3), K53-4 or K52-1 (C5) are also used, the rest - KM-6. Instead of diodes KD521A (VD4, VD5), any of the KD521, KD522 series will do. Transistors VT1, VT2, VT5 - any low-power npn structures with a voltage Uke of at least 20 V. Instead of transistors KT940A (VT3, VT4), KT3117, KT602AM are suitable. LEDs HL1, HL2 - AL307 with any letter index. We will replace the ZP-3 piezoceramic emitter with ZP-5, ZP-22. There are no special requirements for the SB1 button, it can be of any type (KM-1, etc.).

Bell with remote control

Transformer T1 is made on the magnetic circuit K20x12x6 of M2000NM-1 ferrite. Windings I, III contain 60 turns of wire PEV-2 0,23, winding II - 4, winding IV - 2x25 turns of the same wire. Windings I, III and IV are made with wires folded in half. Between the primary windings and winding IV, it is necessary to lay two layers of varnished cloth. The magnetic circuit K20x12x6 can be replaced by K16x10x4,5, while the winding data remains unchanged.

Starting to establish the device, first of all, check the correct installation. Then the converter is supplied with a voltage of 24 V from any power source. The converter should immediately start working, which is confirmed by the glow of the LEDs HL1, HL2. If this does not happen, you need to check the correct connection of the windings of the transformer T1. Further, by placing a jumper instead of the SB1 button, by selecting elements C8 and R12, it is necessary to bring the frequency of tonal bursts closer to the natural resonance frequency of the piezoelectric emitter, which will ensure the greatest volume of its sound. After that, turning off the power source and removing the jumper, you should make all the necessary connections and connect the bell to the AC mains.

Literature

Integrated circuits: Microcircuits for telephony. Issue. 1. - M.: DODEKA, 1994.
Bas A. et al. Sources of secondary power supply with a transformerless input. - M.: Radio and communication, 1987.
Biryukov S. Calculation of a network power supply with a quenching capacitor. - Radio, 1997, No. 5, p. 48.

Author: I.Yushchenko, Sverdlovsk, Luhansk region, Ukraine

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