In this article, we shall learn to make a musical bell. For this, we shall only use three basic electronic components.

These components are (i) IC UM 66; (ii) Transistor BC 548; and (iii) Speaker. The energy source for the bell is two pencil cells fixed in a cell holder.

First things first. Let us learn about the role of each of the component.

IC UM 66 is a melody generating IC.  It has very low power consumption. It is a three pin IC and looks like a transistor.  It works in voltage range from 1.5 V to 4.5 V. The specifications of its pins are:

Pin 1:  Melody Output

Pin 2:  Supply Voltage or Positive Supply

Pin 3: Ground or Negative

When power is given to the IC, it generates musical signal or current, but the signal is very weak and we will not be able to listen to it if given directly to loud speaker.

Transistor BC 548. The level of the signal generated by UM 66 is raised by using a transistor. Transistor has three pins Base, Emitter and Collector. The transistor acts as an amplifier and amplifies the output received from UM 66.

Speaker. The amplified signal is given to speaker. The function of speaker is to convert this electrical signal into melodious sound.


These three components are to be connected in a particular sequence to generate the musical tone. This sequence of connections is called a circuit. The circuit diagram of the bell is drawn below. The lines drawn connecting various components are the connections to be made by soldering using connecting wires.


Connections are to be made according to the circuit diagram. We can call it Wiring Sequence.

Wiring Sequence

Pin 1: Base

Pin 2: Speaker

Pin 2: Positive of the cell holder

Pin 3: Emitter

Pin 3: Negative of the cell holder

Collector: Speaker

By connecting the wires in the above sequence and attaching two pencil cells to the circuit, we can hear a mesmerizing melodious sound of the bell.

This is the basic concept behind the working of a musical bell. We shall discuss a step-by-step construction of the bell in the next article. Watch out!!!