Electronic doorbell circuit

Electronic doorbell circuit

The figure shows the electronic doorbell circuit, which consists of multivibrators VT1, VT2 and power amplifiers VT3, VT4.

When the push button switch SB is turned on, the multivibrator starts to oscillate. R1 and R4 are the collector load resistors of transistors VT1 and VT2. The resistors R2 and R3 respectively add forward bias to transistors VT1 and VT2. Capacitors c1 and c2 are charged alternately to make the transistors work normally and generate audio oscillation. The parameters of the two transistors should be as consistent as possible. If the parameters are inconsistent, the oscillator will eventually stop working. If this happens, the resistance value of R2z or R3 can be appropriately adjusted to make the multivibrator oscillate. The oscillation signal is amplified by the power amplifier composed of transistors VT3 and VT4 and sent to speaker B, making the speaker sound. Changing the capacity of capacitors c1 and c2 can change the tone.