Voice controlled music lantern circuit

The circuit of the lantern controller is as shown below. R1, R2, D and C form a resistor step-down half-wave rectifier circuit, which outputs about 3V DC power for the SCR control loop. The piezoelectric ceramic piece HTD serves as an acoustic-electric transducer. Normally, W is adjusted so that the BG collector outputs a low level, the SCR is turned off, and the colored lights do not light up. When the HTD receives the sound wave signal, the BG collector level increases and the SCR is turned on, so the colored lights can flash and glow with the rhythm of the music played by the indoor radio. W can be used to adjust the voice control sensitivity. When W is adjusted from large to small, the voice control sensitivity will be higher. However, if W is too small, the light will always be on, and the voice control function will be lost. When debugging, gradually reduce W from large to a certain resistance value. , the light will light up, and then move W back a little (i.e. turn it up slightly), the light will go out. At this time, the voice control sensitivity is the highest, and the ordinary conversation sound two or three meters away from the HTD can make the colored lights flash. If the sensitivity is too high, just increase W. If the light stays on, it means that the BG amplification β value is too small, and the transistor with a larger β should be replaced. The resistors are all 1/8W carbon film resistors.