LED voice-activated lights for school trials

The sound-controlled LED light circuit diagram is mainly composed of a sound pickup (electret condenser microphone), a transistor amplifier and a light-emitting diode. When static, VT1 is in a critical saturation state, causing VT2 to cut off. LED1 and LED2 do not emit light. R1 provides a bias current to the condenser microphone MIC. After the microphone picks up the acoustic signal in the indoor environment, it converts it into a corresponding electrical signal, which is passed through the capacitor. C1 is sent to the base of VT1 for amplification. VT1 and VT2 form a two-stage direct coupling amplifier circuit. As long as the appropriate R2 and R3 are selected, there will be no sound wave signal. VT1 is in a critical saturation state, so that VT is in a cut-off state, no current flows through the two LEDs and they do not emit light. When the MIC picks up the sound wave signal, an audio signal is injected into the base of VT1, and the negative half cycle of the signal causes VT1 exits the saturation state, and the collector voltage of VT1 rises. VT2 is turned on, and LED1 and LED2 light up. When the input audio signal is weak, it is not enough to make VT1 exit the saturation state. LED1 and LED2 remain off. Only when a strong signal is input, the photodiode lights up. Therefore, LED1 and LED2 can flash and light up and down with the intensity of environmental sound (such as music, speech) signals.