In the world of electronics, sound-generating circuits are both fascinating and widely applicable. Whether it’s in greeting cards, toys, doorbells, or alert systems, the ability to produce a melody on demand adds a human touch to electronic devices. One such simple yet effective project is the Melody Tone Generator Circuit. At the heart of this circuit is the UM66 melody IC, a low-power CMOS IC that can play a pre-programmed musical tune.
The melody tone generator circuit is easy to build, requires few components, and works on a small voltage supply ranging from 1.5V to 3V. With the help of a couple of transistors, the weak melody signal from the UM66 is amplified enough to drive a small speaker and produce audible music. This makes it a perfect choice for beginners who are just stepping into electronics, as well as for DIYers who want to add audio features to their creative projects.
Let’s explore the components, circuit design, and applications of this fun and useful project.
Component Details
Component
Specification / Description
UM66 IC
Melody generator IC (CMOS, pre-programmed melody, low power operation)
BC547
NPN Transistor for signal amplification (max 100 mA)
BC337
NPN Transistor for driving the speaker (higher current gain)
Resistor
10kΩ, limits current to transistor base
Speaker
1W to 2W output speaker
Power Supply
1.5V to 3V DC (battery or regulated source)
Wires/PCB
For making circuit connections
UM66 IC Pinout
Pin No
Name
Function
1
VSS
Ground (0V)
2
VDD
Power Supply Input (+1.5V to +3V DC)
3
O/P
Melody Signal Output (low power audio tone)
BC337 Transistor Pinout
Pin No
Pin Name
Description
1
Collector
Connected to one end of the speaker
2
Base
Triggered by BC547 output
3
Emitter
Connected to ground
Circuit Diagram
Circuit Explanation
Powering the Circuit The UM66 IC is powered by a low voltage source (1.5V–3V DC). Pin 2 (VDD) receives the positive voltage, and Pin 1 (VSS) is grounded.
Melody Output Once powered, the UM66 begins playing a preset melody. The output (Pin 3) gives a weak audio signal that isn’t strong enough to drive a speaker directly.
Amplification Stages
BC547 acts as a preamplifier. It takes the weak signal from the UM66 and boosts the current.
BC337 is a power amplifier stage. It takes the signal from BC547 and drives the speaker.
Speaker Output The amplified signal is sent to the speaker. The BC337 handles the required current to operate a 1W–2W speaker effectively, generating clear melody tones.
Applications
Application
Purpose
Greeting Cards
Play music when opened
Toys and Games
Add sound effects and melodies
Doorbells
Simple melody-based door chimes
Alarms and Alerts
Audio indication for alarms and notifications
Learning Projects
Great for students to understand audio electronics and transistors
