Tone Generators – Application to Develop Melody & Siren

What is a Tone Generator?

A tone generator is a signal generator circuit which converts applied electrical signals to audio signals. It can be used to produce dial tones in telephones or produce sirens in ambulances or VIP vehicles etc or to generate melody tunes in toys, door bells etc. It can send electrically generated audio pulses to specific components. It can also be used to test the audio equipments.

It basically creates an electric signal and converts it into sound. Different type of tone generators generates different audio signals depending on the application. The source from which the electronic signal is applied also varies with the application.

2 Melody Generator Circuits

• Melody Generator Using IC UM66:

IC UM66 is a small transistor type IC with 3 pins. It is a ROM IC with a prerecorded music inside. When power is applied, IC oscillates and its output gives the music notes. It is necessary to amplify the output in order to hear through the speaker. For this, a single transistor amplifier is sufficient. IC UM66 works well in 3 volts but the power supply can be up to 4.5 volts. So a Zener diode based regulated power supply is used. If the supply voltage is 3 volts (2 pen cells), there is no need for the zener and the power supply can be directly connected to the IC. Here 9 volt battery is used to get loud sound. When power is applied, IC oscillates and the sound can be heard through the speaker. You can use a small 2 inch (4 ohms) speaker or a Mylar speaker (one used in toys). It can be used in toys and door bells.
This is a simple battery operated Music bell circuit that generates a sweet melody for one minute when it is triggered. It uses the ROM IC UM66 to produce the melody. The music stops automatically.

A push switch is used to trigger the circuit. When the push switch is pressed momentarily, NPN transistor T1 conducts and pull the base of T2 and it also conducts. When T2 conducts, C1 charges and provides power to IC UM66. Zener diode ZD is used to regulate the supply voltage to UM66 to 3 volts. When UM66 gets 3 volts supply, it oscillates and the music tone from it will be amplified by T3 which can be heard through the speaker. Use a small 2 inch speaker.

• Musical Door Bell using IC 3481

Generator IC UM 3481. The circuit requires only low voltage from 1.5V to 3V for its operation so that pen cells can be used for the purpose. The circuit requires only a few discrete components in addition to the Melody Generator IC.

About the Melody Generator

IC UM3481 is a Multi-Instrument Melody Generator IC designed for the purpose of Melody generation in various gadgets. It is widely used in Door bells, Alarm systems, Reverse horns, Toys, Clocks, and Timers etc. Its important features are:

1. Low voltage operation from 1.5V to 3Volt.
2. 8 beat selectable.
3. Low standby current.
4. 3 timbers like Piano, Organ and Mandolin.
5. 512 note memories up to 16 songs.
6.  5 tempos available through mask setting .
7. 8 playing modes by user setting.
8. 14 tones selectable.
9. One built in RC oscillator.
10.  On-Chip envelop modulator and Pre amplifier.

The UM3481 series is a mask-ROM-programmed multi-instrument melody generator, implemented by CMOS technology. It is designed to play the melody according to the previously programmed information and is capable of generating 16 songs with 3 instrument effects: piano, organ and mandolin. It also includes a pre-amplifier which provides a simple interface to the driver circuit.

Absolute Maximum Ratings

DC Supply Voltage …………………………………… -0.3V to +5.0V

Input Voltage Range ………………………………… Vss-0.3V to Vdd+0.3V

Operating Ambient Temperature ……………….. 0°C to +70°C

Storage Temperature ………………………………… -10°C to +125°C

Types

There are different versions of 3481 series Music Generator.

IC UM 3481

It can generate 8 song tunes like Jingle bells, Santa claus coming to town, Silent night Holy night, Joy to the world, Rudolph the Red nosed Rein deer, We wish to you a Merry Christmas, O come All Ye Faithful and Hark The Herald Angels Sing.

IC UM 3482

It generates 12 tones like American Patrol, Rabbits, Oh My Darling Clemantine, Butterfly, London Bridge is Falling Down, Row Row Row your Boat,Are You Sleeping, Happy Birthday, Joy Symphony, Home Sweet Home, Weigenlied and Melody On Purple Bamboo.

IC UM 3485

It generates only 5 tunes like The Hawaiian Wedding Song, Try To Remember, Aloha OE, Love Story and Yesterday.

It is very simple to make a Music generator using ROM IC UM 3481. This IC has a programmed oscillator inside. Only a 100K resistor and a 33 P capacitor are sufficient to set the oscillating frequency of the IC’s internal oscillator. Since the output is feeble, a transistor amplifier using a general purpose transistor like AC 187, BC548 etc can be used to amplify the sound.
The IC is a low power one and works between 3-5 volts. If higher power supply is used, a 3 volt Zener regulated power supply should be used. It works well in 2 pen cells. Speaker should be small 1-2 inch 4-8 ohms one. On each press of Push switch, the music tone changes.

A  Siren Generator using IC UM3561

IC 3561 is a tone generator that can produce 4 sirens like Police Siren, Ambulance Siren, Fire brigade siren and Gun sound. The sound depends on the connections in its pin 6.

1. Pin 6 – No connection – Police siren
2. Pin 6 – Connected to pin 5 – Fire engine siren
3. Pin 6 – connected to ground – Ambulance siren

Like UM66, IC 3561 also works in 3 volts and the maximum voltage that can be tolerated is 4.5 volts. So a Zener diode based power supply is used for the IC. Resistor R2 is 220 K which is responsible for the oscillation of the IC. Do not change this value. If it is changed, the tone will be different. Output from the IC is amplified by T1. Speaker can be a small 2 inch 4 ohms speaker or Mylar speaker. You can use a three way switch to select different tones.

I hope you have understand the concept of the tone generator and its applications if any furthermore queries on this concept or on the electrical and electronic projects leave the comments below.