Traditional Chinese European and American alarms: Circuit Design, Parts List & Workshop Prototype Guide

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European and American alarmsPeople pay special attention to whether the sound of the alarm is eye-catching and unique. People can see in European and American movies and TV dramas that the European two-tone alarm sound and the American screamer type alarm sound are not only fast-paced, giving people a tense and comfortable feeling, but also can make people distinguish the obvious difference from fire fighting, ambulance and other alarm sounds.Two alarm sound circuits in Europe and the United States are introduced below for enthusiasts to follow.1. Circuit working principleThe circuit principle block diagram of European and American alarms is shown in Figure 20-1.Figure 20-1In the figure, AMV is an astable multivibrator. When switch S1 is placed in the A position, the square wave output from the astable multivibrator by the American-type alarm is directly sent to the control input end of the voltage-controlled oscillator VCO. Its output signal causes the VCO to switch back and forth between two frequencies (ie, the European alarm frequency f1 and the American alarm frequency f2).When switch S1 is placed in the E position, it is a European alarm. The output signal of the astable multivibrator AMV first passes through the integral low-pass filter, and the signal output from the low-pass filter is approximately between a sine wave and a triangle wave. When the voltage controlled oscillator VCO is driven by this signal, the sound it makes is similar to the noisy noise of American police chasing criminals. When this output signal causes the VCO to switch back and forth between the two frequencies, it emits a screaming alarm sound.The circuit diagram of European and American alarms is shown in Figure 20-2.Figure 20-2In the figure, transistors BG1 and BG2 form a non-multivibrator AMV. When switch S1 is placed in the "E" (European type) position, the timing control circuit is composed of adjustable resistor P1, fixed resistors R2 and R3, and capacitor C2. Among them, the function of P1 is to adjust the "conversion frequency".When switch S1 is placed in the "A" (American type) position, adjustable resistor P2, fixed resistor R3 and capacitor C2 form a timing control circuit. Among them, the function of P2 is to adjust the "screaming speed". If you need to get a better alarm sound effect, you can add any number of pre-adjusted potentiometers and change the timing time to get different alarm effects.Adjustable resistor P3, fixed resistor R10, capacitor C5 and transistor BG3 form an integral low-pass filter. Among them, the function of P3 is to adjust the amplitude of this level's output signal, and then use this output signal to adjust the difference between the highest frequency and the lowest frequency of the American-type alarm.Transistors BG4~BG7 form the voltage controlled oscillator VCO. The input terminal of the voltage controlled oscillator is the base of triode BG6, and the voltage of the base determines the output frequency. For American type alarms, this control voltage is the output voltage of the integrating low-pass filter. This voltage rises and falls with the rhythm of the non-multivibrator AMV, so the output voltage of the voltage-controlled oscillator VCO also rises and falls with the rhythm of the non-multivibrator AMV. Among them, the function of P6 is to adjustAmerican type alarm screamer center frequency.For the European-type alarm, the square wave output of the non-multivibrator AMV is directly added to the voltage-controlled oscillator VCO, so the voltage-controlled oscillator VCO alternately generates two frequencies. The adjustable resistor P4 adjusts the difference between the two frequencies, and the adjustable resistor P5 adjusts the lower frequency of the two frequencies. Therefore, the difference in frequency can be used to adjust the higher frequency.2. Component selection and debuggingIn the figure, each component selects its relevant value according to the following:R1, R16, R17 2.2kΩR2, R3, R5, R20 100kΩR4, R8, R9, R11～R14 1kΩR153.3kΩ R1822kΩR1912KΩ P1 and P2 are 470KΩ potentiometersP3 is 100KΩ potentiometerP4 is a 22kΩ potentiometerP5 and P6 …

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