UM66 is a melody generating IC commonly used in calling bell, phone, toys, musical bell in doors, home security alarm systems, burglar alarms etc. It is a three pin IC looks like a transistor. Its first pin is ground, second is VCC and the third is the melody output. Supply voltage that can be given to the IC is in the range of 1.5V- 4.5V. These are CMOS ICs and have very small power consumption. Melody generator will reset when the power is turned on and then the melody begins from the first note.
The melody generator has an inbuilt beat and tone generator. The time base for beat and tone generator is an inbuilt oscillator. Tone generator and beat generator are programmed divider. Tone generator produces certain frequency. These frequencies are a factor of the oscillator frequency. Beat generator contains 15 available beats. Of these four beats can be selected. It has a 62 notes ROM to play music. A set of 4 bits controls the scale code while 2 bits control the rhythm code.