Home > Group Projects > Musical Toy Project
Project concept by Phil Townshend - copyright 1998.

UPDATED:.22:31 22 October 2013

A 8-10 week project that is ideal for Key Stage 2 or 3 D&T.

This project is possible due to the UM66T melody IC. A (thankfully growing) range of tunes are avaiable which use very few components to drive a loudspeaker. These tunes can be used as part of a MDF or acrylic toy that has a part of it that moves to activate the tune. This can be any feature of the model, eg. arm, hair etc

The project covers Electronics and mechanics, from melody ICs and transistor amplifiers to levers and cams.


The lever has to be attached behind the model to activate the microswitch. A 4x1/2 japaned wood screw was used to secure the lever.

The microswitch is screwed into place from the front of the model using countersunk screws then the heads painted over to hide them, or they can be stuck with impact adhesive.


The battery box made from 6mm MDF, holds the 2xAA battery holder which is wire ended, not the snap type. Parts were glued together with PVA glue and then sanded smooth.

Another method of activating the microswitch when the lever is attached to the front of the model using a screw.

The speaker can be glued with impact adhesive, but it is preferable to have screws with washers positioned at 3 points around the rim holding the lip of the speaker intoplace. The screw are very small, 6.5mm so they don't go through to the other side.


  • 6mm MDF or 3mm Acrylic
  • 3mm MDF offcuts
  • PCB & Components
  • Small length of insulated wire
  • PVA Glue
  • 6.5mm self tapping screws
  • 12mm self tapping screws
  • Wirecutters and Screwdriver
  • Soldering iron, stand and wire
  • Drill, 3mm bit, 2mm bit
  • Saws and sander
  • Paints

A good tip is to glue the battery box in to place about 3mm from the bottom of the model. This makes it lean back very slightly and a lot more stable

There are confusingly 2 types of melody IC available - or there were:
  • M66T, UM66T series
    This type can drive a speaker directly.
  • HT38xx series
    This type requires a transistor to drive a speaker.

The M66T is available from Maplin but I haven't seen the HT series for a while. Refer to datasheet/part no. when you order to determine which type you have.

When using the HTxx type, take care as the melody IC and the transistor are in the same package.The transistor can be any TO92c, such as BC337.
Look up the NPN transistor table for various common types.

Circuit Diagram - M66T series

Circuit Diagram - HTxxxx

The circuit board only measures 30mm x 20mm, so it's small enough to be supported on wires attached to the speaker - shown left. The wire is tinned copper wire, or single core wire with the insulation taken off. This is strong enough to support the PCB and allows it to be folded neatly around the back of the speaker - shown right.

Go to Maplin website to see the range of tunes available, although the page with the IC data on doesn't exist atm, you can see it on their e-catalogue.

Left shows how to connect the battery, switch and PCB together. The connections are the same for either circuit.

You will need to either cut the positive lead, or add another wire to link the microswitch to the PCB. It depends how much wire you need.

Ensure that the positive connection (red wire) is on the right and the negative on the left.

Put a piece of masking tape on the back of the speaker to prevent the metal case shorting out the underside of the PCB.

To prevent the battery wires breaking away from the PCB, drill 3mm holes in the PCB to feed the wires through to take the strain.

Previous work

Some projects were made from 3mm acrylic with relief parts in different colours - (shown right). This looked very effective and professional when completed but it is difficult to do.
Instructions on assembling the PCB, connecting the speaker, and the battery supply.
Instructions on assembling the PCB, connecting the speaker, and the battery supply.
24 PCB layouts of both types of PCB. These can be photo-copied onto acetate.
A chart for working out the 3 band resistor colour coding system.
Useful compact cards that have a reduced version of the chart above.
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