As seen in the diagram the main stages of the circuit is built-in inside the musical chip in the form of oscillator, frequency divider, drive ROM, a ROM having 512 musical tunes, a tone generator, rhythm generator, timbre generator, modulator, run off control, and a pre-amplifier stage.
Besides the IC, the circuit also consists of an AC to DC power supply with a voltage regulator stage, a push-pull amplifier for generating a loud musical output from the speaker.
The frequency of this multi tune musical door bell is determined by the resistors R1, R2, potentiometer P2, and capacitor C2 for the oscillator stage built inside the IC.The preset decides the run-off speed, meaning how fast the tune can be played.
The resistor R7 and capacitor C4 guarantee ideal working conditions for the internal IC modulator stage.Resistor R3, preset P1 and capacitor C3 are configured like a volume control stage for the chip's internal pre-amplifier.To operate the circuit there are a few press buttons included as S1---S3, along with the resistor R3----R6.
Push button S2 is wired like a usual bell push button.In order to play a pre programmed melody, there's a provision for this in the form the push button S2.
Pressing S1, all the tunes which saved inside the IC will be played one after the other in a sequence.
When S1 is in the switch OFF position, only a single melody is played as selected by S3.
To select a desired specific melody, you must close the button S1, and then press S2 continuously, with S3 being pressed repeatedly ON/OFF until you find the right one as per your preference.
The chip UM3481 has 8 numbers of Christmas carol melodies, UM3484 includes the Big Ben striking one to twelve with ascending sequence.
The chip UM3482 for this musical doorbell comes with a pre-programmed 12 tone melody, which include:
"Frere Jacques, trHre Jacques",
"Happy Birthday to you", and "Cradle Song",
while the UM 3483 contains melodies like "The Last Rose of Summer", "The Lorelei", and"Wedding March"
Parts List
PCB Design and Component Layout for the Musical Doorbell
