UM3561 Siren Circuit – Make 4 Realistic Sounds with 3V Only!

Here are a few sound-effect generator circuits using the UN3561 IC and a handful of other components. It is capable of generating four different sounds, which are an ambulance siren, a police siren, a fire engine siren, or even a space machine gun sound, all from a relatively small, simple, and inexpensive circuit.

Typically, if we wanted a siren sound generator circuit, we would use the NE555. However, it is quite complicated to use, and its performance is modest; thus, we will use the UM3561 instead.

What is UM3561?

UM3561 CMOS LSI is a sound generator IC that can produce 4 types of siren sounds (ambulance, police, fire engine, and space sound) using very few external components. It works on a 3V supply and is ideal for small DIY sound circuits.

Features

• Three alarm sounds and one sound effect
• Typical operational voltage of 3V—min. 2.4V and max. 3.6V, normally sufficient with two 1.5V AA batteries. 
• Typical operational current of 150μA
• Capable of driving a magnetic speaker with the help of an NPN transistor
• Maximum output current of around 3mA 

Pinout

It uses the same DIP-8 package as a NE555, meaning that it is fairly easy to use. The descriptions of each individual pin are as follows:

1.  SEL2 is the sound effect selector pin.
2. VSS is a negative power supply (GND).
3. OUTPUT is monotone output.
4. NC is used for testing—leave open in normal operation.
5. VDD is a positive power supply.
6. SEL1 is the sound effect selector pin.
7. OSC1 is an RC oscillator pin.
8. OSC2 is an RC oscillator pin or inverted clock output.

Sound Generator Circuits Using UM3561

Let’s take a look at some of the example circuits.

Practical 4 Sound Effects Generator Circuit

Finally, let’s look at a circuit suitable for general use; it is louder and more practical than the previous circuits. Part of that change is the sound selector; using a combination of switches is tedious, so we are replacing it with a 4-position selector rotary switch instead.

How it does works

Similar to the previous circuit, R1 is connected to pin 7 and pin 8 of IC1, which are OSC1 and OSC2, respectively; it controls the frequency of the oscillator inside IC1. The lower the value of R1, the higher the frequency; conversely, the higher the value, the lower the frequency.

The positions of S1 for each sound are as follows:

1. Police car siren—pin 6 (SEL1) and pin 1 (SEL2) are left disconnected.
2. Fire engine siren—pin 6 (SEL1) connected to VDD, pin 1 (SEL2) disconnected.
3. Ambulance siren—pin 6 (SEL1) connected to VSS, pin 1 (SEL2) disconnected.
4. Space machine gun sound—pin 1 (SEL2) connected to VDD, pin 6 (SEL1) disconnected.

How to build

Because this circuit only has a few components, it can be assembled on a universal perforated PCB. But we are going to build ours on a dedicated PCB as shown in the picture below. 

We use this 12-pin, 3-pole, 4-position, selectable signal deck band selector rotary switch for the sound selector. You can check it out here.

Testing

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