Siren Circuit using 2N2907 Transistor — The Engineering Knowledge

Hello, readers welcome to the new post. Today we will discuss Siren Circuit using 2N2907 Transistor. You daily have seen that fire truck produces sound through siren as passes through traffic. It is that siren circuit that we will discuss like that ambulance siren circuit. The working operation of that siren is very simple and easy to understand. Here we will cover the details of the inner circuit and the details of working of this project.

In this circuit we are using 2N2907 transistor, transistor is an electronic component that is used as a switch and amplifier. It has three pinout base emitter and collector. Base work as control this control and regulate the power supply value to this module. Using this component we make a circuit of a siren and practically will see how this work. Let get started

Introduction to 2N2907 Transistor

  • It has a high current of about six hundred milliamperes and operates at low volts and forty volts.
  • It has forward biased condition when the base is attached to the ground and for the reverse-biased state, there is no current pass.
  • Its dc gain value is one hundred to three hundred which indicates the amplification features of this component. So it is part of the amplifier and switching circuits
  • In the case of a completely biased state, there are five milliamperes highest current passes through the collector pin and VCE is 1.6volts this is the saturation state of this module
  • If there is no base current existing at the transistor it is in cut off region

2N2907 Transistor Features

  • The main features of this component are discussed here
  • Its operating temperature is minus sixty-five to one fifty
  • Dc gain is about one hundred to three hundred
  • Power dissipation is four hundred milliwatt
  • VEB is five volts
  • VCBis sixty volts
  • VCB is sixty volts
  • collector base volts is forty volts
  • It comes with Lead-free packaging
  • It has TO-92 and TO-18 packaging
  • Its value for low volts re forty volts It has a maximum current of about six hundred milliampere

2N2907 PNP Transistor Pinout

  • There are three main pinouts it has’
  • EMitter: Current comes out from this point
  • Base: Work as a control for components like tap
  • Collector Larger than the other two parts and get the supply

Siren Circuit Overview

  • In this project, we will make a circuit through the use of very simple transistors and loudspeakers that help to use in different offices homes, and building as security operation
  • There are two main components of this project which are 2N2222 and 2N2907 transistors that are operating as astable multivibrator mode of 555 timers.

Project Components

  • The components used in this project are listed here
  • Resistors
  • Transistors
  • Speaker
  • Battery
  • PCB from PCBWAY: PCBWay is a PCB manufacturer and PCB assembler. You can get PCBs for your project creation from this high-quality service provider. Shenzhen has been a world center for electronics research, development, and manufacturing for decades. By cutting out all the middlemen, they are successfully transitioning to savings and bringing total satisfaction to their valued customers in purchasing PCB/PCBA. That’s why 100% of their old customers come to them for their future orders.
  • There are different testing performed with additional basic visual inspection for PCBs at PCBWAY. Common tests performed at PCBWAY are Flying Probe Tester, X-Ray Inspection Machine, and Automated Optical Inspection (AOI) Machine. In a single day, they have 50+ new engineers around the world using their PCBs for their work who trust them due to their high quality
  • A one-stop PCB assembly and prototyping solution that provides some of the most innovative PCB technology and the highest quality standards in the industry. DFM, Gerber files, bill of materials, invoices, and inspection reports are in your orders.
  • The main purpose of PCBWAY is to provide high-quality, less expensive, and fast delivery to its customers.
    In terms of cheaper electronic projects, it is the first PCB supplier to provide PCB prototyping service at the price of $5/10pcs.
  • If you use the coupons after a new registration, the price will be reduced to zero dollars. Thye provides a template for ten dollars and also has a similar price for different colors of solder mask. The delivery time of the product is usually two to three days.
  • Thye also comes with live customer support service for their users if you have any problems can contact them at any time.
  • Their team will carefully observe your order from start to end and also have an observation to the final reach of the order to you
  • You can track your order by using their customer support service

Circuit Explanation

  • The construction of this circuit is very easy and simple through the use of transistors. This circuit produces a sound like a siren. It occurs due to the collective configuration of PNP and NPN transistors.
  • Here we are using 2N222 and 2N2907 transistors with an eight-ohm loudspeaker that has enough strength to generate the required sound.
  • There is also an option to use old fashion loudspeakers that play music.
  • Her two-transistor combination work as the multivibrator. If we on the circuit rough apply the supply from a battery of nine volts the first capacitor starts charging and gets the highest level. With the charging of the capacitor decreases the time constant at R2/C2 junction increases the frequency of the multivibrator that is the combined effect of two transistors
  • When the power supply is off charging of the capacitor becomes slow that resulting in reducing of frequency. The sound generated from the speaker will increase or decreases as the power supply is connected or removed means switching on and off


  • Applications of this circuit are discussed here
  • It used in security system
  • Ambulance alarm
  • Industries to control any critical situation
  • Used in defense system to handle the warning
  • A police van has this alarm

That is all about the Siren Circuit using 2N2907 Transistor all details has explained if you have any questions ask here. Further do not miss to use the PCBs from the best PCB suppliers PCBWAY

Author: Henry

I am a professional engineer and graduate from a reputed engineering university also have experience of working as an engineer in different famous industries. I am also a technical content writer my hobby is to explore new things and share with the world. Through this platform, I am also sharing my professional and technical knowledge to engineering students.

Originally published at on October 27, 2022.



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