Electronic rhythm control circuit

In this circuit, the double-pole double-throw switch S2 is connected
to the speaker. The capacitor CI passes through the speaker and is connected to the base-
emitter of VT1 . Capacitor C2 is connected in parallel to the base-emitter of VT2 through R2.
Turn on the power switch Sl. The power supply passes through RP and R. To C. Charge. Since the resistance of RP and
Ri in series is very large, charging is very slow. When C． When the voltage on the capacitor reaches about
0.7V, VT1 is turned on, and the power supply
quickly charges capacitor C2 through the collector-emitter of VT1. Make VT2 conduct quickly and the speaker will sound.
    At this time, capacitor C. It discharges through the base-emitter of VT1, the negative terminal and
the positive terminal of the power supply, and the emitter-collector of VT2. When the voltage across Cl drops to a very small level, VT1 is cut off. However, VT2 cannot be cut off immediately
. Only when the capacitor island is discharged through the emitter base and resistor of VT2, and the voltage at both ends drops to close to zero, can VTZ be turned off.
    Changing the resistance of RP can change the charging time of Cl by the power supply and change the beat frequency. If you move S2 to the light bulb position, the beat
sound will turn into a flash.