Discrete component sound and light control stair delay switch circuit (10)

It is a sound and light controlled stairway delay lighting switch that uses a positive feedback audio amplifier. Its
sound control sensitivity is relatively high. At night, ordinary conversations or footsteps can trigger the light E to light up.
    The basic principle of this circuit is similar to the above example. VTI-VT3 constitutes a positive feedback audio amplifier. As long as
microphone B senses a weak sound wave signal, Vding3 will quickly cut off, its collector potential will rise, and VT5 will be turned on.
The 12V power supply charges ' through wrs and VD2, and its subsequent circuit is exactly the same as Example 159. VT8 is turned on,
and the lamp E is powered on and emits light. In order to make the light control performance of the circuit stable, compared with Examples 1, 5 and 9,
a separate light-controlled electronic switch tube VT4 is added to this side. VT4 is turned on during the day, and the base of VT5 is short-circuited to ground to make it have no output.
Only in the evening, when VT4 was cut off, was the blockade on VT5 lifted. This circuit works stably and has
good performance. The requirements for components are the same as the above example. If necessary, the bias resistor R of the VTI needs to be adjusted. ,
just make the gain of the positive feedback audio amplifier appropriate.