Siren Circuits you can Build at Home

In this post we learn about a 2 simple siren circuits, using Arduino and also with ordinary components such as transistors and capacitors yet is able to produce an alarm sound at an excruciating level.

The idea was contributed by "Abu-Hafss"

Deeper in the article we also learn to make an advanced Arduino based design with adjustable and customizable tone features.

The Design

This simple car siren circuit design explained here uses minimum number components and yet is able to produce an ear piercing alarm sound each time it's switched ON.

The device is normally used as a car reverse horn, although it can used for any other relevant application too, depending upon the user's preference.

In the automobile field this siren is also popularly know as the "Mega Siren" due to the massive decibel level it generates.

The schematic details and other related info of the proposed car siren is presented below,which were furnished by Mr. Abu-Hafss, who is one of the dedicated readers and contributor of this blog.

Circuit Diagram

PCB Layout

The following request was also attached with the above files in the email from Mr. Abu-Hafss.

Dear Swagatam Attached,

please find a photo of a car 12V-20W siren which has really ear-piercing sound. I opened it and found a small PCB as attached.

I have interpreted the PCB into schematic as attached. My concern is to use the amplifier section for some other 15-20W application.

Frankly, I do not have practical experience of audio amplifiers. I shall highly appreciate your help in this regard.

Best regards

Abu-Hafss

As per the above request, the amplifier section of the car siren is cheap and powerful (@ 20watts) and possibly could be used as an amplifier module for other applications requiring a cheap but powerful amplifier alternative.

Analyzing the The Design

Studying the given diagram it appears that the stage comprising Q4, Q5 is only responsible for the amplification, the remaining sections are for generating the siren frequency for the Q4, Q5 base.

The stage forms a powerful Darlington transistor amplifier stage with an extremely high gain (in the order of 1000 and more)

Since the amplifier design is too basic, it might not be suitable for generating or handling Hi-fi music or frequencies above 4kHz.

Moreover the transistor in the process could dissipate a significant amount of heat causing the consumption to be higher than the normal Hi-fi amplifiers.

Therefore, although the amplifier incorporated in the above car siren circuit is cheap and simple it cannot be efficiently implemented for producing movie songs and melodies which involve frequencies up to 15kHz. However, it can be effectively used in units such as horns, bells, alarms, security systems etc.

2) Generating Siren Sound with Arduino

The following Arduino based siren sound generator circuit can be used for generating the pitch perfectly imitating a typical siren sound and can be customized to produce many different siren effects simply by making relevant modification in the sketch.

A siren sound, as we all know is a loud noise generated through a device designed for producing this sound either through a mechanical approach or through electronic circuits.

Siren sound generator devices find many useful applications and are used in emergency service vehicles like in police and ambulance vehicles, and also in fire brigades etc.

The discussed configurable siren enables a connected speaker to produce a custom siren sound. Basically there are two types of siren sound generating equipment, viz pneumatic and electronic.

Pneumatic systems employ air pressure forced through an appropriately dimensioned pipe for creating the sound, while electronic equipment are more sophisticated, using loudspeakers or piezo devices for generating the relevant sound at any desired rate and pattern. Electronic sirens are more flexible, customizable and offer more variations and are extremely efficient.

Types of Siren Sound

A Siren sound can be of many different types, a few common types are the police, ambulance, and the fire siren, others could be in the form of mega sirens as used in car horns, some are fast police siren tunes, another type could be ear piercing such as used for neutralizing mobs, a few could be in your cell phone for alerting while a new message is received.

Therefore, the range could be too extensive and the proposed Arduno alarm circuit can be customized as per the users personal wish and preference for achieving the wished siren sound.

Code sketch:

/*
Siren

A configurable siren for Arduino, requires an 8-ohm speaker attached to
pin8 and ground. For high amplification use a transistor driver with pin8

//Copyright (c) 2012 Jeremy Fonte
//This code is released under the MIT license
//https://opensource.org/licenses/MIT
*/
const int pitchLow = 200;
const int pitchHigh = 1000;
int pitchStep = 10;
int currentPitch;
int delayTime;
const int speakerPin = 8;
void setup() {
currentPitch = pitchLow;
delayTime = 10;
}
void loop() {
tone(speakerPin, currentPitch, 10);
currentPitch += pitchStep;
if(currentPitch >= pitchHigh) {
pitchStep = -pitchStep;
}
else if(currentPitch <= pitchLow) {
pitchStep = -pitchStep;
}
delay(delayTime);
}

Arduino Wiring Diagram with Speaker and Supply Input

 Video Demo:

Using a BJT Stage for Greater Amplification

For high amplification, the above set up can be modified as per the folowng connection diagram:

Modifying the Code

Upon Testing I fund the siren sound from the Arduino not very pleasant, and had slight distortions. I experimented with the code, and finally made it extremely smooth and pleasant to hear. Here's the improved for you:

//Improved by Swagatam
*/
const int pitchLow = 200;
const int pitchHigh = 1000;
int pitchStep = 10;
int currentPitch;
int delayTime;
const int speakerPin = 8;
void setup() {
currentPitch = pitchLow;
delayTime = 5;
}
void loop() {
tone(speakerPin, currentPitch, 20);
currentPitch += pitchStep;
if(currentPitch >= pitchHigh) {
pitchStep = -pitchStep;
}
else if(currentPitch <= pitchLow) {
pitchStep = -pitchStep;
}
delay(delayTime);
}

You can also play with the const int pitchHigh = 1000;and increase to to 2000 for increasing the siren length, which is relevant to police sirens.

Police, Ambulance, Fire Brigade Siren - USA Style

The next siren circuit is a 3-in-1 siren, which will produce 3 distinct tones resembling, police siren, ambulance siren, and fire brigade sirens sound.

These can be selected through a 3 pole switch, and simply by toggling the positions of the switch.

The complete circuit diagram for this 3 in 1 siren circuit is furnished below: