Summer Vacation Workshop for

School Childrenon

“Musical Door Bell ”24-25 April 2015

Department of Electronics Shivaji University, Kolhapur

The “UM66” Melody IC

UM66T is a melody integrated circuit. It is designed for use in bells, telephones, toys etc. It has an inbuilt tone and a beat generator. The tone generator is a programmed divider which produces certain frequencies. These frequencies are a factor of the oscillator frequency. The beat generator is also a programmed divider which contains 15 available beats. Four beats of these can be selected.

There is an inbuilt oscillator circuit that serves as a time base for beat and tone generator. 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. When power is turned on, the melody generator is reset and melody begins from the first note. The speaker can be driven by an external npn transistor connected to the output of UM66.

Many versions of UM66T are available which generate tone of different songs. For example, UM66T01 generates tone for songs ‘Jingle bells’, ‘Santa Claus is coming to town’ and ‘We wish you a merry X’mas’.

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Circuit Schematic

Fig 1: Circuit Diagram of Simple Musical DoorbellRef: UM66 Datasheet, Unisonic Technologies Co., Ltd.

Fig 2: IC UM66 Fig 3: Transistor

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Pin No Function Name1 Melody output Output2 Supply voltage (1.5V - 4.5V) Vcc3 Ground (0V) Ground

Table 1: Pin Configuration of IC UM66

Resistance Color Code

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Speaker In order to translate an

electrical signal into an audible sound, speakers contain an electromagnet: a coppor coil which creates a magnetic field when an electric current flows through it. This coil behaves much like a normal (permanent) magnet, with one particularly handy property: reversing the direction of the current in the coil flips the poles of the magnet.

Inside a speaker, an electromagnet is placed in front of a permanent magnet. The permanent magnet is fixed firmly into position whereas the electromagnet is movable. As electricity passes through the coil of the electromagnet, the direction of its magnetic field is rapidly changed. This means that it is in turn attracted to and repelled from the permanent magnet, vibrating back and forth.

The electromagnet is attached to a cone made of a flexible material such as paper or plastic which amplifies these vibrations, pumping sound waves into the surrounding air and towards your ears.

The frequency of the vibrations governs the pitch of the sound produced, and their amplitude affects the volume

--- http://www.physics.org/article-questions.asp?id=54

Inside a speaker:1. Cone2. Electromagnet (coil)3. Permanent magnet

Transistor Amplifier