Audio circuit diagram with 555 as the core

As shown in the figure, the audio circuit consisting of 555 is the core, and all work in a multi-resonant state. This circuit is generally used in ambulances dispatched by hospitals.

Audio circuit

In the figure, the illustrated parameters can be used to determine the oscillation frequency of the two oscillators.

When RP1, when the resistance of potentiometer RP1 changes from 0 to 75kΩ, the corresponding frequency is 14.4~0.9Hz.

The duty cycle of the oscillating waveform is determined by the formula D=t/T, so the maximum duty factor of the first-order oscillating waveform is 47%. IC2 is controlled by the low frequency square wave of IC1. When the output square wave of IC1 is low, the oscillation frequency of IC2 becomes low; when the output of IC1 is high, the oscillation frequency of IC2 becomes high, and a rhythmic sound is emitted from the speaker. Changing the time constant of R3, R4, and C2 will also change the acoustic frequency of the output.

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