Electronic music flashing light circuit

The electronic music flashing circuit can use sound or flashing to display the rhythm. The beat frequency can be
continuously adjusted from a dozen times per minute to a hundred or dozens of times per minute. It can be used to practice singing and playing, and can also be used to tell time in a dark room.
    The circuit description is as follows: In this circuit , the double-edged double-throw switch S2 is in the position of the speaker. Capacitor c1 is connected to
the base and emitter of VT1 through the speaker. Capacitor c2 is connected to the base and emitter of VT2 through R2. Turn on the power switch Sl, and the power
is charged through RP, Ri, and Cl. Since the resistance of RP and R in series is very large, charging will be slow.
When the voltage on c] reaches about 0.7V, VT1 is turned off, and the power supply
quickly charges c2 through VT1, so that VT2 is quickly turned on, the speaker sounds, and the light bulb flashes at the same time.
    At this time, the capacitor C discharges through the base, emitter, negative terminal, and positive terminal of the power supply of VT1,
and then through 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. It must wait until the capacitor C2
is discharged through the emitter base of VT2 and the resistor Rz, and the voltage at both ends drops to close to zero
, before VT2 can be cut off.
    Changing the resistance of RP changes the charging time of the power supply to C, and also changes
the music flashing frequency.