Discrete component sound and light control stair delay switch circuit (9)

A sound and light controlled stairway delay lighting switch with a unique circuit design , which has high
sound control sensitivity. At night, when someone walks on the stairs r, the sound of footsteps will turn off the electronic meter and turn on the light
. After the person leaves, there will be no sound for 30 seconds and then the light will go out on its own.
    Vn3-VD6 form a bridge rectifier circuit, through R. Step-down and current-limiting, vs. voltage stabilization, the filter outputs about
9V DC voltage to power the transistors VT1-VT4. During the day, the photoresistor RL has low resistance, VT3 is on, and
VT4 is off. At this time C. When the voltage rises, VT:i is cut off, VT6 is turned on, and the gate and cathode of the thyristor VT7
are short-circuited by VT6. VT7 is disconnected and light E does not light up. At night, RL has no light and has a high resistance, but
the bias effect of R "makes VT1 conductive. VT1 emits a current to flow to the base of VT3, so that VT3 is still in a conductive
state, so in a quiet state, the light It will still not be lit up.
    When someone is walking on the stairs J, and the sound of their footsteps or conversation is picked up by the microphone B, the corresponding electrical signal will be output and
sent to VI for amplification. After the audio signal is released, it is injected into the base of VT3 from the emitter of VD1.
  On the other hand, is captured and output by the VT1 collector through C. Coupled to the base of VT2, the signal is amplified by VT2 and
sent to the base of VT1 again. It can be seen that VT1 and VT2 form a TF feedback audio amplifier,
which has extremely high circuit gain, so that the circuit has high voice control sensitivity. This is the ingenuity of this circuit design
. Since the VT3 base plate has a strong audio signal input, the negative half cycle of its signal causes VT3 to exit the conduction state and
enter the amplification state or even the cut-off state. VT3 collector current ft rises. vr4 is turned on, and 9V DC voltage passes through VT4 and
VD2 to (, is quickly charged, and passes through R. T5 is turned on, VTfi is cut off, and
the blockade . The gate of V T7 is stopped by R-. To trigger the current, VT7 is turned on, and the lamp E lights up.
After the lamp is lit, its own light makes R1J become a low resistance, causing VT3 to conduct and block, but because C. is full of charge, C
passes through R. The emitter junction of VT5 is discharged, so that VT5 can still maintain the conductive state, so the lamp continues to light up. When
the discharge is completed, VT5 is cut off, VT6 is turned on, VT7 is turned off, and the lamp goes out. If there is a sound again, the lamp will turn off.
Lights up. The delay time IHj of the circuit is determined by the discharge time constant of R. and G. The data shown in the figure is about 3.s. During the
day, due to the VT3 blockade, no matter how loud the sound is, the lamp will not light up.
    wri , VT:/ requires the amplification p value to be greater than 200. The p value of other transistors is preferably around 100. The pVceo requirements of VT5 and VT6 are as high as possible. It is best to use the electret condenser microphone B with a white point
with better stability.
The one with the package label. Other component parameters are shown in the figure, no special requirements.