The post explains how to make a simple 220V mains operated ding dong bell circuit which will generate a powerful ding dong sound each time someone presses the bell push button.
This bell produces the classic “Ding-Dong” bell sound but does not use mechanical parts. With an integrated one designed for such use and some more components the same effect is achieved and in solid state (no moving parts).
Each time the bell is pressed the Ding-Dong generator creates a weak audio signal with the sound of the bells. The signal is raised in volume by the amplifier and is reproduced by the speaker. The power supply provides the circuit with the voltage needed to operate. The interface allows the circuit to be connected to centrally-fed tones such as buildings or door intercom.
Power Supply for the ding dong bell circuit
The circuit obtains power from the position marked V + and ground. The main section of it is the integrated HT2811, manufactured by the Korean firm Holtek. Pin 1 generates the clock signals, enabling the chip to create the “Ding-Dong” audio. Pins 2 and 3 are associated with RC sets the two tones of the sounds (2 = “Ding” / 3 = “Dong”). Modifying these elements is achievable to change the sound quality of the bell. Pin 4 refers to the volume. Pin 5 outputs the sound signal which is amplified with a couple of general purpose transistors in darlington setup. Terminals 6 and 7 tend to be linked with a 680K resistor which modifies the gain of the chip’s interior preamplifier. Ultimately terminal 8 powers the chip that is restricted in current through the resistance of 100 ohms as well as stabilized to 3.3v through the zener diode. The 100μF capacitor filters the probable residual ripple content in the supply line.
Replacing with reed relay interface instead of the push button switch
In a situation where it is far from possible to change the network of the bell button, this particular control panel can be used. It gets an alternating or continuous voltage at the input and rectifies it with the rectifier bridge PR whose steady output is filtered through the capacitor of 470μF and then strikes the coil of a little reed relay. The main element of this relay activates the main circuit similar to a standard pushbutton. The rectifying bridge (PR) could be assembled using by diodes of 1A 250V or more rating. Please ensure that the voltage of the relay coil is identical to the voltage of the primary buzzer of the earlier buzzer (usually 12v). Even though relay could be powered without having rectifying or filtering the line, it is far from practical since the alternating current might result in the relay to behave like a buzzer, activating and deactivating its pole 50 times per second which could cause some problems for the system in the course of time.
This part of the circuit derives the voltage of the house electrical network for powering recommended the equipment. Aditionally it enables to feed the set together with batteries for situations when the power supply outage. The transformer decreases the voltage to 4.5v AC. The rectifier bridge (PR) changes alternating electric current into DC, which happens to be filtered by the 2200μF capacitor. The 1N4007 diodes work as a source selector by working the system together with mains or batteries as required. The fuse safeguards the 220v portion of the transformer. The rectifying bridge (PR) could be any device whose voltage can be more than 250V and whose current is simply not under 1A. The + V point signifies the output of the supply, while the batteries (4 in series) connect across the + Bat and -Bat points.