Introduction to simple and practical voice-activated electronic doorbell circuit

When using this circuit as a doorbell, it is not necessary to install a push button switch in front of the door. The visitor only needs to click on the door and the doorbell will sound. The circuit is as shown.

The biggest feature of the circuit is the use of the speaker for vibration input, and the doorbell output.

The transistor V2, the potentiometer KP and the capacitor C2 constitute a control circuit, and V1, V3, R2, and C1 constitute a complementary oscillator. When the switch S is turned on and the power is turned on, the power supply charges the C2 through the BE junction of C2 and V2 and the speaker BL. The larger instantaneous charging current makes the V2 saturation turn on, clamping the collector potential of V3; after the charging of C2 is finished, The power supply provides a base current to V2 via KP to maintain the critical saturation state of V2, rendering the oscillator inoperative. When the external acoustic wave vibrates the speaker cone, an induced voltage is generated across the speaker. This voltage is applied to the emitter of V2, causing V2 to exit the critical saturation region and enter the amplification region. The voltage drop between the collector and the emitter of V2 increases. Thereby the oscillator oscillates and the BL emits an audio call. Release the call to disconnect S and then close. VI selects 3DG6, 3DG6, B>=80; V3 selects 3AX31, B>=60; V2 selects 3DG6, B>=100. BL selects 8 um speaker and installs it in the upper middle part of the inner side of the door panel. The transistor transistor is a device composed of three layers of impurity semiconductors, and has three electrodes, so it is also called a semiconductor transistor, a transistor, etc., and can be used for detection, rectification, amplification, switching, voltage stabilization, signal modulation, and many other functions.