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 NXP Semiconductors


  • Musical Doorbell Sound

  • Created: Aug 28, 2014

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Description

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Summary

The design is a modified type of doorbell. Instead of having a common buzz sound for doorbell, a musical sound will be produce which is more pleasing to hear. A short melody is played after button S1 is pressed and when it is pressed many times in rapid succession or pressed longer, a different melody is generated and it plays loger.


The design is comprised 74HC4015D device is a dual 4-bit serial-in/parallel-out shift register that acts as the main component of the circuit. The circuit work in such a way when the button S1 is activated the inputs of U3 and one input of U1 switches to logic “0″. The data input (pin 7 of 74HC4015D) becomes logic “1″. Each clock impulse coming from U4 shifts this logic “1″ further in the register. The clock frequency is around 5 Hz. The number of shifted logic “1″ is directly dependent on the length of time the switch S1 is closed. Once at least one shift register is logic “1″, a current flows to the base of T1 through a corresponding resistor. The transistor T1 functions as a current controlled oscillator. The tone pitch is dependent on the logic state of the different flip-flop outputs of the shift register. Each clock pulse shifts the logic “1″ in the register. One output of the register (pin 2) is coupled back to U2 and U3 so that all the logic “1″ in the register always run in a loop. After S1 is released, the register runs until the capacitor C1 gets discharged through R2. When S1 is again pressed (closed), the capacitor C1 stays charged causing the musical bell to play continuously. The difference between the two ways of activating the switch S1 is that different combinations of logic “1″ inputted into the shift register. These different combinations produce the different melodies played by the circuit. The musical doorbell must be connected to an audio amplifier. The supply voltage is not critical. It can be between 5 and 15 volts. The circuit consumes around 15mA.


The design is quite innovative. It seems that the exacerbation problem regarding the buzz sound of some doorbells will now be solved. It can give ease to most of the commercial and residential users and even in the part of industrial application. It is excellent and can be mass produce.

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