Siren sound effects digital synthesizer. Encyclopedia of radio electronics and electrical engineering

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

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Digital synthesis of audio signals has recently become more and more widespread. Unlike analog, digital synthesis methods provide higher accuracy, relative simplicity of circuit implementation and high reproducibility of design solutions. This article discusses the basic version of the sound effects synthesizer for a fast police and slow “howling” fire siren. Reproduction and repetition of effects is performed automatically.

Unlike analog synthesis, which requires fine tuning of the frequency of reference sinusoidal oscillators, digital synthesis can significantly simplify circuitry, thanks to the use of counters with a variable division ratio of the KR1564IE7 type, which can significantly reduce the number of microcircuits used [1]. The KR1564IE7 counter is a frequency divider with a variable division ratio. It is controlled by a digital code that enters the inputs of the parallel loading of the counter. This code is a binary number corresponding to the equivalent weight expression of the counter division factor. And if this code is changed with a certain clock frequency, then at the output of the KR1564IE7 microcircuit, a number of frequency divisions of the master oscillator will appear - a tone signal, the frequency of which changes according to a certain law [2].

The law of tone signal frequency change can be set, for example, as a linearly increasing and decreasing sequence of binary codes formed using an eight-bit reversible counter. In such a case, the equivalent numerical expression of the binary code may vary, for example, from zero to the maximum value and vice versa. Changing the rate of rise and fall of the binary code can also be selected by hardware, which will mean changing the rate of rise and fall of the siren tone.

(click to enlarge)

The electrical circuit diagram of a digital synthesizer of siren sound effects is shown in Fig. 1. The synthesizer consists of tunable LF and HF generators, elements DD1.1, DD1.2 and DD1.3, DD1.4, respectively; electronic key DD2.1; pre-divider with variable division ratio DD3; reversible counter-former of binary codes according to the law of increase and decrease DD6, DD7; decoder-limiter of the maximum and minimum values ​​of the code sequence DD8; divider with variable division ratio DD9, DD10; trigger-divider-shaper meander DD11.1; trigger states "start" - "stop" DD11.2 and the counter of the number of repetitions of periods of sound effects of the siren DD12. The signal from the trigger-divider output is fed to a key amplifier made on transistors VT1 ... VT3. The synthesizer is powered through an integral stabilizer of the KR142EN5A type, installed on the device board.

The synthesizer is launched by a short positive pulse with an amplitude of 5V with a duration of at least 100 ns or by briefly pressing the SB1 button. In this case, the trigger DD11.2 is reset to the zero state and the signal from the direct output enables the operation of the trigger DD11.1 and the counter DD12, and the signal from the inverse output unlocks the counters DD6, DD7 and enables the operation of the generators DD1.1, DD1.2 and DD1.3 , DD1.4. At this point in time, the generator on the elements DD1.1, DD1.2 operates at the minimum frequency set by the tuning resistor R2, since the electronic key DD2.1 is closed and the resistor R4 is disabled. The output rectangular pulses of the generator are divided by the counter DD3, the division ratio of which is set by jumpers S1 ... S4. At the initial time, the counter DD12 is in the zero state, so the level of a logical unit is formed at the output of the element DD4.4. Consequently, the division ratio of the counter DD3 is maximum and equal to 15, since all its preset inputs D0 ... D3 (pins 15, 1, 10, 9) receive levels of logical units.

The initial state of the counters DD6, DD7 corresponds to the maximum binary code, since before the reset of the trigger DD11.2, the inputs of the preset "C" (pins 11) of the counter data were affected by a logic zero level. In this case, the logic zero level generated at the output of the most significant bit "15" (pin 17) of the decoder DD8, through the jumper S6 resets the RS-flip-flop DD5.1-DD5.2 to the zero state. The operation mode of counters DD6, DD7 is defined as subtraction. This state of the device corresponds to an increase in the tone of a slow “howling” fire siren.

Rectangular pulses from the output of the RF generator with a frequency of about 100 kHz are fed to the subtraction input of the counter DD9, and from its output to the subtraction input of the counter DD10. At the output of DD10, a tone signal is generated corresponding to the current count of the binary code coming to the inputs of the preset counters DD9, DD10. The pulses at the output of DD10 have a large duty cycle (reverse duty cycle), therefore, they require the use of a trigger-divider DD11.1 to form a meander. The integrating chain C3R9 increases the output pulses in duration for a clear trigger DD11.1.

When the counter DD7 reaches the zero state, the output "0" (pin 1) of the decoder DD8 generates a logic zero level, which sets the trigger DD5.1 ​​to a single state, thereby changing the mode of the counters DD6, DD7 to summation. At the same time, a negative pulse is formed at the output of the DD4.3 element, which, with its positive drop, increases the state of the counter DD12 by one. Now, thanks to the operation of the counters DD6, DD7 in the summation mode, the tone of the calling slow siren decreases. The change in the states of the counter DD7 is indicated by a line of LEDs HL1 ... HL14.

When the counter DD12 passes to the second state and the diode VD1 is installed, a logic unit level is formed at the output of the diode decoder VD1 ... VD7, which opens the key DD2.1 and sets the maximum frequency of the generator DD1.1, DD1.2, which corresponds to the start of playing the sound effects of a fast police siren. Next, three full periods of a fast police siren will be generated, after which a positive pulse will be generated at the output "9" (pin 11) of the counter DD12, transferring the trigger DD11.2 to the initial single state. Now the device is ready for a new start.

The device is assembled on a printed circuit board (Fig. 2) with dimensions of 150 x 90 mm from double-sided foil fiberglass 1,5 mm thick. The device uses ICs of the K561, KR1564 series, fixed resistors - MLT-0,125, tuning resistors - SP3-38b, capacitors - non-polar type K10-17, oxide - type K50-35, LEDs HL1 ... HL14 - type AL307AM, BM, integral stabilizer DA1 - type KR142EN5A, button type KM1-1. ICs of the KR1564 (74HCxxN) series are interchangeable with the corresponding analogues of the KR1554 (74ACxxN) series.

Setting up the device consists in setting the desired siren tone frequency using resistor R6 and jumpers S5, S6, as well as the repetition period using resistors R2, R4 and jumpers S1 ... S4. A device assembled from serviceable parts and without errors works immediately when turned on.

Literature

1. Cherevatenko V. and A. Programmable musical bell-automatic: Sat: "To help the radio amateur.", Vol. 103, p. 52. - M.: DOSAAF, 1989
2. Cherevatenko V. and A. Melodious signaling device. - “Radio”, 1992, No. 8, pp. 12-15.

Author: Leonidovich O.A.

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