In the circuit shown in the figure when we press S1, capacitor C1 charges slowly, and with that it activates the relaxation oscillator so that its frequency increases smoothly until it reaches a maximum point determined by the setting of P1 and the value of C2. When we release S1, capacitor C1 is discharged by the relaxation oscillator, and with that the frequency of the produced signal decreases until it stops completely. The produced signal is applied to the power FET that excites a speaker with good power.
