NE555 makes a pleasant doorbell

Here is a pleasant doorbell circuit. The 555 timer chip (IC1) in the circuit is connected as a multivibrator. Its output lasts for 7ms when it is low and lasts for 235ms when it is high. When the output of IC1 becomes low, transistor T2 is turned on, activating the buzzer, which sounds and charges capacitor C3. When the output becomes high, the sound intensity of the bell gradually fades. This process is repeated until the timing circuit stops working.

The working process of the timing circuit is as follows: Short press switch S1 causes capacitor C1 to charge rapidly through R1. When the voltage across C1 exceeds the gate threshold voltage of field effect transistor T1, T1 begins to conduct, and this conduction state will continue as long as the charge on C1 makes the voltage greater than this threshold voltage. If the component values ​​used in the circuit are used, the buzzer will beep for about 15 seconds, and its beeping sound is very pleasant. This time is enough for the owner to hear.