Adding Sound to your Models
By Tim Surtell

The 'playability' factor of many Meccano models can be considerably enhanced if they are capable of producing suitable sound effects. For example, a military model could could emit the sound of gunfire, a model of an emergency vehicle could have a wailing siren, and a model steam locomotive could produce a 'chuff-chuff' sound.

Producing the sound of gunfire, or any other type of sound, would be tricky to do but for several special sound effects ICs which are available to easily do the job. Because these ICs have been designed for use in toys, they are easy to use and require minimal external components. Unfortunately, they do not all have the same facilities, and so they all have different application circuits.

Siren and Machine Gun Sounds

The UM3561 sound effect generator IC would be a good choice for models of emergency vehicles since it produces police car, fire engine, and ambulance siren sound effects. Which effect is played is determined by the connection of pin 6 to Vs, 0V, or nothing, as shown in the table below:

Sound Effect

Pin 6

Police Car Siren

No Connection

Fire Engine Siren


Ambulance Siren


In addition, a pulsating machine gun sound effect, which could be useful in a military model, can be played at any time by connecting pin 1 to Vs.

Datasheets UM3561 Sound Effect Generator IC - PDF format (213kb)

The pin-out of the UM3561 is shown in figure 1. Pin 1 is the pin on the bottom left when the IC is held horizontal with the writing the correct way up.  The little notch in one side also helps to identify pin 1, as does the small white dot next to this pin.

Figure 1: Pin-out diagrams of the UM3561 IC and BC107B transistor

The IC's power supply (3V DC) should be connected between pins 5 and 2. The sound effect output from pin 3 can be connected either to a piezoelectric sounder or to a small 8Ω, 0.2W loud-speaker via a BC107B transistor.

In the circuit diagram of figure 2, pin 6 has been connected to the common terminal of an SPDT centre-off switch so that any of the three siren sounds may be be produced when the power is on. The machine gun sound effect can be played by pressing the Gun button when the power is on. Of course, should you only need to use one of the effects, you could hard-wire pins 1 and 6 as appropriate.

Figure 2: The UM3561 sound effect circuit

Playing a Tune

Several versions of the M66T melody generator IC are available, each of which plays a common tune such as "Happy Birthday" or "Jingle Bells". These ICs are powered from 1.2V to 3.6V DC, and are extremely easy to use: just connect up the power and a small 8Ω, 0.2W loud-speaker as shown in figure 4. No other components are required.

Datasheets M66T Melody Generator IC - PDF format (50kb)

Figure 3: Pin-out diagram of the M66T   Figure 4: The M66T melody generator circuit

Building the Circuit

A stripboard layout for the UM3561 sound effect circuit shown in figure 2 is given in figure 5, and it will allow all four sound effects to be produced.

  1. Cut a piece of stripboard to 15 tracks x 21 columns.
  2. Fit the 5 wire links.
  3. Fit the 10kΩ and 420kΩ resistors.
    Fit the 8-pin IC socket, taking care to align the notch as shown in the layout. Do not insert the UM3561 at this time.
  4. Fit the BC107B transistor. Place a crocodile clip around each leg of the transistor before soldering. This 'heat shunt' will prevent the heat from your soldering iron damaging the transistor. Try to keep the soldering time to a minimum for this component.
  5. Insert the UM3561 into its socket, taking care to align the notch with the notch in the socket.
  6. Cut the copper tracks where an X is shown.
  7. Connect up the button, SPDT switch, and the loudspeaker as shown.
  8. Connect up a 3V DC power supply and test the circuit.

Figure 5: A stripboard layout for the UM3561 sound effect circuit

Article Information
Source: Electronics in Meccano - www.eleinmec.com | First published in EiM: Issue 9 (September 2000)
Topic: Analogue Electronics | Created: 2/18/2007 | Last modified: 2/18/2007

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