Door Ringer Circuit with Melodic Tone

Figure 1 

The circuit was designed to create a melody ringer that will be used for main door entrances.

• 7413 – a dual Schmitt trigger with input gating that has different thresholds for positive- and negative-going inputs used for pulse shaper and threshold detector due to its features such as typical power dissipation 42mW per function, typical propagation delay of 17ns, temperature compensated design, operation from very slow ramp voltages, and 800mV hysteresis typically for higher noise immunity
• BC550 – an NPN general purpose transistor with low current and low voltage used for low noise stages in audio frequency equipment
• BC560 – a PNP epitaxial planar Silicon enclosed in a 24-pin dual in-line package or 3-pin TO-92 package typically used for switching and AF amplification due to its low noise and high voltage features

In most houses, the main entrance doors have bells installed that converts electric current into chimes, rings, and buzzes. The design of this circuit is for the purpose of possibly changing the intensity and the tone of audio from the door ringer. This will be done through the values of the components used in this circuit such as the capacitor and resistor values. From the components specified in the list of parts, the frequency of the circuit will fall at approximately 2 KHz and 5 KHz.

The circuit will start to function upon applying pressure to the switch and will last for only a short period of time. During this incident, a visual indication will simultaneously show from the LED D2 aside from the sound being heard. Other types of sounds can be created by changing the capacitors C2 & C3. The circuit drives an 8R speaker with 0.5 W of power.

Figure 2 

This type of melodic door ringers or doorbells are now coming with a wide range of styles and innovation wherein some wireless doorbells have different shapes and colors. Some wall mounted door ringers include bell push and plug-in chime where 32 chime sounds can be chosen. In order to avoid interference with neighbor chimes, a digital code system is used. The circuit is highly available in the market since it has low power consumption and powered by a 9 V battery for those designs with remote control.

Source:users.otenet.gr/~athsam/melody_door_ringer.htm