Melody generator schematic

This tiny circuit comprising of a single 3 terminal IC UM66 can be built small enough to be placed inside a greeting card and operated off a single 3V flat button cell. There is not much to the circuit. The UM66 is connected to its supply and its output fed to a transistor for amplification. You can either use a 4ohm speaker or a flat piezoelectric tweeter like the one found in alarm wrist watches. If you use the piezo, then it can be connected directly between the output pin 1 and ground pin 3 without the transistor. More: The UM66 looks like a transistor with 3 terminals. It is a complete miniature tone generator with a ROM of 64 notes, oscillator and a preamplifier. When it first came into market, it was programmed for the "Jingle bells" tune. Now they come with a wide variety of different tunes.

The described circuit utilizes the UM66 integrated circuit, which is a compact and efficient tone generator ideal for applications requiring sound output in a limited space, such as greeting cards. The UM66 features three terminals: power supply, ground, and output. When powered by a 3V button cell, the IC draws minimal current, making it suitable for battery-operated devices.

The circuit design is straightforward. The power supply pin connects to the positive terminal of the battery, while the ground pin connects to the negative terminal. The output pin delivers the audio signal, which can be amplified using a transistor for driving larger speakers, such as a 4-ohm speaker. The transistor is connected in a common emitter configuration, where the base is driven by the output of the UM66, allowing for greater sound volume.

Alternatively, a flat piezoelectric tweeter can be directly connected between the output pin and ground. This configuration eliminates the need for amplification, as piezoelectric devices can efficiently convert the electrical signal into sound without additional components.

The UM66 is equipped with an internal ROM containing 64 different musical notes, along with an oscillator and preamplifier, enabling it to produce a variety of melodies. Initially, the chip was released with a default tune, "Jingle Bells," but subsequent versions include a wider selection of pre-programmed tunes, making it versatile for various applications. The compact nature of the UM66 and its simple interfacing requirements make it an excellent choice for sound generation in small electronic projects.This tiny circuit comprising of a single 3 terminal IC UM66 can be built small enough to be placed inside a greeting card and operated off a single 3V flat button cell. There is not much to the circuit. The UM66 is connected to its supply and its output fed to a transistor for amplification. You can either use a 4ohm speaker or a " flat" piezoelectric tweeter like the one found in alarm wrist watches.

If you use the piezo, then it can be connected directly between the output pin 1 and ground pin 3 without the transistor. The UM66 looks like a transistor with 3 terminals. It is a complete miniature tone generator with a ROM of 64 notes, oscillator and a preamplifier. When it first came into market, it was programmed for the "Jingle bells" tune. Now they come with a wide variety of different tunes. 🔗 External reference