On the pages of popular publications have been published describing the different variants of the acoustic switches.
Propose another scheme that I developed and produced more than nine years ago, and since then it works flawlessly in the hallway of my apartment. The scheme has a time relay. After the filing of a short beep, the light in the hallway comes on and remains lit for about four minutes, then automatically turns off. The scheme itself is imbedded in the wall, the walls are papered.
No switches in the hallway no, the Wallpaper is clean, which rarely happens when there is a switch, and children constantly use them.
The scheme works as follows. The sound signal perceived electret microphone WM, is supplied to chip DA1 (microphone amplifier with special frequency response), used in radio stations type of "LEN". With the circuit output signal is sent to the shaper rectangular pulses, assembled on two inverter circuits DD1, and further to the base of transistor VT1, which when opened, discharges the timing capacitor (C3) of the Schmitt trigger. Thus on the output element of the trigger DD1.4 appears a logical "O", and turns on the multivibrator is made on the chip DD2.
At the output of the multivibrator is a pulse amplifier (VT2, VT3), the output of which through a blocking capacitor C7, the signal applied to the control electrode of the triac VS1. The triac is opened and includes the load. When the capacitor C3 is charged to the logic level "1", the Schmitt trigger switches to another stable state, the output DD1.4 appears logical "1", the multivibrator is switched off, closes the triac and the light bulb goes off. The exposure time is selected depending on the particular application of the circuit. When nominal capacitance C3 specified in the scheme, the burning time of lamps is 4 minutes. Led VD5 you can apply any.
Author: V. Lazovic, Makeyevka; Publication: N. Bolshakov, rf.atnn.ru