Alarm generators. Encyclopedia of radio electronics and electrical engineering

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Using a modern element base, it is possible to simplify the design of generators that act as signaling devices in various devices. This is discussed in the proposed article.

One of the main elements of simple signaling generators is a sound emitter. All proposed designs use an imported electromagnetic capsule with a diameter of 12 mm for an operating voltage of 6 V with a built-in generator. The capsule remains operational when the supply voltage drops to 1 V. When a voltage of 6 V is applied to it (observing the polarity!) A relatively loud sound with a frequency of about 2000 Hz is heard.

The devices also have a flashing red LED with a diameter of 8 mm and a brightness of 800 mCd. Turning it on in series with the capsule (Fig. 1), we get the simplest signaling generator. By applying power to such a node, you will hear intermittent beeps. The current consumption of the device during the signal is about 15 mA.

If a slight decrease in volume due to a voltage drop across the LED does not suit you, you can assemble a generator using a field effect transistor (Fig. 2). As long as the LED is off, the voltage across the resistor is low and not enough to turn on the transistor. When the LED flashes, the voltage across the resistor reaches 4 V, the transistor opens, the capsule starts working at maximum volume, since the voltage drop across the transistor at a current of 20 mA does not exceed 50 mV. There are no self-induction pulses at the terminals of the capsule, therefore, it is not necessary to install a protective diode, as is done in similar cascades with a conventional capsule.

On fig. 3 shows a diagram of a generator with input voltage control. So, if, when moving the engine of the tuning resistor R1, the voltage at the base of the transistor VT1 becomes less than 0,6 V, it will close. But on the other hand, the VT2 transistor will open, the BF1 capsule and the HL1 LED will start working.

Such a generator can be used, for example, in a short circuit buzzer described by the author in "Radio", 2001, No. 10, p. 58, instead of a node on the chip. The signaling device will now become light and sound.

With the specified capsule, it will be possible to build a simple phone call signaling device (Fig. 4) or just a bell for a telephone set. When a telephone call signal arrives, the alternating voltage is rectified by the VD1 diode bridge, after which the rectified voltage is smoothed by the capacitor C2 and limited by the zener diode to a voltage that is safe for the capsule. If the zener diode is replaced by three LEDs of the KIPD36 series connected in series, they will glow during a call.

A simple light and sound photorelay can be assembled according to the scheme shown in Fig. 5. While the illumination of the photodiode VD1 is sufficient, the field-effect transistor VT1 is closed, a generator similar to the one whose circuit was shown in fig. 2 does not work. When the illumination of the photodiode becomes less than the threshold voltage at the gate of the transistor VT1 increases. As soon as it exceeds approximately 1,5 V, the transistor VT1 opens, the generator turns on. There will be sound from the capsule and LED flash.

If you swap the resistor R1 and the photodiode, the generator will turn on when the illumination of the photodiode increases to a certain value. The required sensitivity of the device is set by selecting the resistor R1.

The device, assembled according to the scheme in Fig. 6, similar to the previous one, but controlled by the sensor plates E1 and E2. While the resistance between them is high, the signaling generator does not work. But as soon as you touch the plates with your finger, the resistance between them will drop, the transistor VT2 will open, the generator will turn on. Transistor VT1, operating in the avalanche breakdown mode, acts as a micropower zener diode and protects the field-effect transistor VT2 from static electricity discharges.

In devices assembled according to the diagrams in Fig. 2-6, it is permissible to use MLT-0,125 resistors, oxide capacitors K50-35, K50-16. Capacitor C1 in fig. 4 - type K73-17, MBM; C1 in fig. 6 - K10-17. Instead of the photodiode FD320, any other one designed for the infrared range is suitable, for example, FD265A, FD-ZK, FD-28KP. The blinking LED can be replaced by any other similar one, suitable in terms of glow color and dimensions, and the KTs407A diode bridge (see Fig. 4) can be replaced with four diodes of the KD102, KD105, KD209 series. Instead of field-effect transistors KP501V (Fig. 7, a), it is permissible to install current switches KR1014KT1A (Fig. 7, b), and instead of the bipolar transistors indicated on the diagram, any low-power npn silicon structures, for example, the KT342 series.

A capsule with a built-in generator can be any other of the indicated series with the index X. The first two digits in the designation are the case diameter, the last two are the maximum operating voltage. After purchasing the capsule, do not forget to remove the self-adhesive label covering the hole.

If any of the light and sound generators will be built into another device, it is advisable to install at least one blocking capacitor with a capacity of 0,15 ... 100 μF along the power circuit. This will prevent the built-in generator from negatively affecting other circuits in the structure.

Author: A.Butov, village of Kurba, Yaroslavl region

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