This is a Doorbell Musical Circuit using IC 4093. After the button S1 is pressed, a short melody is played. When the button is pressed many times in rapid succession or pressed longer, a different melody is generated and the melody plays longer.
When S1 is released (opened), 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 continously.
The difference between two ways of activating the switch S1 is that different combinations of logic “1″ are inputted into the shift register. These different combinations produce the different melodies plyed 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.
S:electronicsuite.com
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