Signaling devices on the blinking light-emitting diode. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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In various amateur radio and industrial developments, audio frequency generators made on digital CMOS microcircuits and piezo emitters are widely used. The simplest generator - a multivibrator - can be performed on just two inverters [1]. However, its sound volume is insufficient in many cases, especially in self-powered designs. It is not difficult to increase the volume using two more inverters from the same microcircuit [2].

However, in some cases, due to the peculiarities of psychological perception, an intermittent sound signal is required (alarm clocks, security devices, etc.). For these purposes, another generator is installed, tuned, as a rule, to a frequency of no more than 2 Hz [3] - it controls the existing generator.

It is not necessary to adhere to such an option. It is much easier to replace the interrupt generator with a commercially available so-called flashing LED ("Flash"). And then the device will be simplified (Fig. 1).

On the elements DD1.1 and DD1.2, a sound generator is made, tuned to a frequency of 1000 ... 2000 Hz. Buffer elements DD1.3, DD1.4 help to increase the volume of the sound of the piezoelectric BQ1. The maximum volume is achieved by selecting the resistor R3. The flashing LED HL1 periodically turns on the generator and at the same time serves as a light indicator of the receipt of a control signal at the input of the device (for example, from a security alarm sensor). By selecting the resistor R2, a reliable switching on of the generator and an acceptable brightness of the LED are established. If there is no signal, the LED is off, the generator is not working.

The device used a small-sized (3 mm in diameter) Japanese blinking red LED L-36BHD, designed for a supply voltage of 5 ... 12 V. Its switching frequency is about 0,7 Hz, however, it is permissible to use a two-color LED with a switching frequency of about 1,5 .XNUMX Hz.

An interesting version of the sound and light signaling devices with three clearly distinguishable modes. To do this, you need to connect two more transistor stages to the main device (Fig. 2).

In this variant, in place of HL2 it is desirable to install a single-color LED with a switching frequency of 0,7 Hz, in place of HL3 - a two-color red-green (almost like in a police "flasher") with a switching frequency of 1,5 Hz, in place of HL1 - a regular LED constant glow. Then it will be possible to get an interesting effect: when a signal arrives at input 2, the piezo emitter will emit rare sounds, at input 3 - more frequent, at input 1 - the piezo emitter will sound continuously. In other words, alarm signals are heard on the rise, depending on the "value" of the protected object. It remains only to correctly place the sensors on the objects and protect them from simultaneous operation.

And two more examples of using flashing LEDs. Firstly, it will be possible to significantly simplify various sirens, for example, the one described in [4, Fig. 1]. There is no need for a DD1 chip, resistors R3-R5 and capacitor C1. A flashing LED is connected by an anode to the base of the transistor VT2. and the cathode - to the common wire. Perhaps, for a more accurate operation of the device, you will have to select a resistor R6.

In amateur radio and industrial guards, a conventional LED is often used, which is installed in the passenger compartment in a conspicuous place and operates in the periodic switching mode. An attacker on the wiring to such an indicator will quickly find the watchman and neutralize it. When using a blinking LED, communication with the watchman disappears, and it can be masked more carefully.

Literature

1. Biryukov S. Generators and pulse shapers on CMOS microcircuits. - Radio. 1995. No. 7. p. 36.37.
2. Vinogradov Yu. Increasing the volume of the piezoelectric sounder. - Radio. 1993. No. 8. p. 39.
3. Vinogradov Yu. Encoder and decoder of the radio channel of the guard. - Radio. 1994. No. 3. p. 30-32.
4. Vinogradov Yu. Piezo siren in burglar alarms. - Radio. 1998. No. 5. p. 44.

Author: A. Martemyanov, Sevsrsk, Tomsk region

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