Flashing lights that make bird calls

The colorful light string is composed of 18 small electric beads. When the colorful light string is connected to the power supply, each small electric bead receives an AC
voltage of about 12V . One of the 18 small electric beads is a "jumping bubble". Its structural principle is similar to the neon bulb of the fluorescent lamp starter.
There is also a bimetallic piece inside . When the power is energized, the filament heats up and causes the bimetallic piece to bend, causing the contacts to jump open. extinguished. After the bimetal piece cools down,
the contacts are connected again, and the lanterns glow. Then the bimetal piece is heated and jumps open, and the lanterns go out... Over and over again, due to the effect of "bubble jumping"
, the string of lanterns can light up and go out at intervals.
    The 12V alternating current taken from both ends of a small electric bead is half-wave rectified by VD, and filtered by C4 to become a smooth direct current for the transistor
VT. VT, L, CI, C2, etc. form a typical inductor three-point audio oscillator. The oscillation voltage is output from both
ends of the inductor coil and added to the piezoelectric ceramic piece B to make it sound. There is a resistor-capacitor network of R2 and C3 connected to the base circuit of VT. Due to
the charge and discharge of the capacitor, the oscillation is blocked, so an oscillation gap is generated, and B emits a "chirp, chirp" sound that resembles a bird's cry
.
    The inductor L and the capacitor Cl determine the fundamental frequency of the bird's call. The values ​​of R2 and C3 determine the frequency of the gap repeating call. By
adjusting the values ​​of C1 and R2, a satisfactory bird's call effect can be obtained. When the colored lights go out and the 12V alternating current is terminated, due to
the discharge of capacitor C4, the bird's chirping will not stop immediately, but will gradually weaken and finally stop, which further enhances the bird's chirping effect
.