Sound signaling devices on dinistors. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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Very simple sound signaling devices can be built on microcircuit analogues of symmetrical dinistors of the KR1125KPZ series, described in Radio No. 5, 1998, p. 59-61, and KR1182KP1 (Fig. 1).

The signaling device with a telephone capsule (Fig. 2) is a relaxation generator, similar to those that are performed on neon lamps or analogs of dinistors. In the initial state, the capacitor C1 is discharged. When a supply voltage of 12 ... 30 V is applied, it starts charging through resistors R1 and R2. As soon as the voltage on it reaches the switching voltage of the dinistor Uper (it is about 8,5; 15 and 21 V for KR1125KPZ dinistors with indices A, B and C, respectively), the dinistor opens and the capacitor quickly discharges through it and the capsule BF1.

After the capacitor is discharged, the current through the dinistor becomes less than the minimum holding current Iud', at which the dinistor remains on and the dinistor closes. The capacitor starts to charge again, the process repeats.

The voltage on the capacitor is close to sawtooth in shape with a smooth rise from zero to Uper and a sharp decline. With the ratings of the elements indicated in the diagram (capsule winding resistance - 90 Ohm) and a supply voltage of 12 V, the frequency of the generated signal can be adjusted in the range from 1000 to 2500 Hz. In this case, the total resistance of the resistors has to be changed from 35 to 12 kOhm (higher resistance corresponds to a lower frequency).

If a voltage of 20 V is applied, the frequency can be adjusted from 650 to 3000 Hz by setting the resistance of the resistors from 120 to 24 kOhm. The higher the supply voltage compared to the switching voltage of the dinistor, the easier it is to fulfill the generation conditions, the wider the frequency change range. The capacitance of the capacitor also affects the frequency - the larger it is, the lower the tone of the sound.

The sound volume of the signaling device is small, but it is enough, for example, when studying the telegraph alphabet. It is not difficult to increase the volume using a dinistor with a large switching voltage (with indices B, C) and a corresponding increase in the supply voltage.

Signaling devices with piezo emitters, for example, ZP-5, have a greater volume (Fig. 3). In this version, the capacitor is not needed - its role is played by a piezoelectric emitter, the capacitance of which is 10 ... 30 thousand pF.

The operation of such a signaling device has some features compared to the previous device. Each discharge of the capacitance through the dinistor causes oscillations in the emitter at its resonant frequency - about 2,5 kHz for ZP-5. Due to the inverse piezoelectric effect, sinusoidal damped oscillations appear at the outputs of the emitter, superimposed on the sawtooth voltage of the capacitance charging (Fig. 4a). As a result, the oscillations of the generated frequency are internally synchronized with the natural resonant frequency of the piezoelectric emitter. Now an attempt to smoothly adjust the frequency (with a variable resistor R2) or a change in the supply voltage will lead to a jump in frequency.

The shape of the voltage on the piezoelectric emitter is interesting when the generation frequency is increased and it is brought closer to the resonant one (Fig. 4b). When trying to "transition" the resonant frequency, the oscillations first become non-periodic, and then (when the generated frequency significantly exceeds the resonant one, which is possible with an increase in the supply voltage) they become sawtooth.

When a supply voltage of 12 V was applied, the frequency of the signaling device could be changed from 500 to 2400 Hz (resistor resistance 32 ... ). Some expansion of the area of ​​​​stable operation of the signaling device can be achieved by connecting a DM-6,5 inductor in series with the dinistor or similar with an inductance of about 20 μH.

By placing a metal plate with dimensions of at least 150x150 mm above the piezoelectric emitter lying on the table and changing the distance between them from 50 to 300 mm, one can observe the effect of sound reflection on the operation of the signaling device. The volume and tone of the sound changes, especially at a frequency close to resonant. If you connect an oscilloscope to the piezo emitter, you will see changes in the voltage shape on its screen.

Since the dinistors of the KR1125KPZ series are symmetrical devices, it is not necessary to observe the polarity of the supply voltage indicated in the diagrams. Moreover, signaling devices are able to work when powered by alternating voltage. So, in the device according to the scheme of Fig. 3, instead of two resistors, one was installed, with a resistance of 130 kOhm and a power of 0,5 W, and it was powered by an alternating voltage of 40 .. 250 V with a frequency of 50 Hz. The sound, however, was harsh, annoying, most appropriate for an emergency call. The approximate shape of the voltage on the emitter corresponded to that shown in fig. 5.

A significant increase in sound volume can be achieved by using a KR1182KP1 dinistor in the signaling device (Fig. 6). Its switching voltage is about 105 V, and it will be applied to the piezo emitter. The signaling device provides a loud sound, similar to a machine gun burst and is well audible anywhere in the apartment. The similarity will become even greater if any diode is connected in series with the resistor R1 for an operating voltage of at least 300 V, for example, the KD105 series. Resistor R2 serves to limit the pulsed current through the dinistor at an acceptable level.

Carrying out experiments with signaling devices powered by the mains, special care must be taken. All changes and soldering must be performed by first disconnecting the devices from the network. The shaft of the variable resistor is turned only with a screwdriver with an insulated handle. In the finished design, the elements of the signaling device must be inaccessible to accidental contact.

Author: S. Biryukov, Moscow

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