220V alternating current is converted into DC pulsating voltage after bulb H and rectification, which is applied to VS and R branches of SCR as forward bias. During the day, when the brightness is greater than a certain level, the photodiode D presents a low resistance state of ≤ 1kω, which turns off the transistor V, and its emitter has no current output, and the unidirectional thyristor VS turns off due to no trigger current. At this time, the current flowing through the bulb H is ≤2.2mA, and the bulb H cannot emit light. The resistor R 1 and the zener diode DW make the bias voltage of the transistor v less than 6.8V, thus protecting the transistor.
When the brightness at night is less than a certain level, the photodiode D presents high impedance state ≥100K Ω, which makes the transistor V turn on in the forward direction, and the emitter voltage is about 0.8V, which makes the thyristor VS trigger on and the bulb H emit light. RP is a brightness selection element, which is used to switch in the early morning or evening. It consists of an audio amplifier, a frequency selection circuit, a delay start circuit and a thyristor circuit.
Just connect a voice switch in series in the circuit. When there is sound, the voice control switch is closed and the electric light is on; The sound disappears, the voice switch is turned on, and the light bulb goes out.
Acousto-optic control circuits are commonly used. When it is dark, the light control switch is turned off and there is no light. When there is sound, the voice control switch is closed, the circuit is connected and the light bulb is on. At dawn, when there is light, the light control switch is turned on. When there is sound, although the voice control switch is closed, the circuit is not connected, so the light bulb does not light up.
Extended answer:
Voice-activated switch: It is an energy-saving electronic switch that uses sound effect to excite the pickup to carry out acoustic-electrical conversion to control the opening of electrical appliances, and can automatically disconnect the power supply after a period of delay. The voice control switch consists of microphone BM, sound signal amplification, half-wave rectification, light control, electronic switch, delay and AC switch circuit. Turn off the voice switch during the day or when the lights are bright; At night or when the light is dim, the voice control switch is ready to work. When someone passes the switch, the sound of footsteps, voices and clapping can start the voice-activated switch (the light turns on), and after a certain delay, the voice-activated switch will automatically turn off (the light turns off).
Reference: Baidu Encyclopedia? voice operated switch