Car Siren Circuit

In this post we learn about a high power car siren circuit which utilizes 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"

The Circuit 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 Schematic

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 Circuit 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.