Electronic siren circuits using transistors


The siren circuits are what importance in various alarm system. For example, the emergency alert, burglar alarm circuits, Fire alarm circuits, Timer , sensor controls, etc. Today I would like to introduce the simple and economical simple siren circuits. It is suitable for beginners. My son will gradually build this circuit onto the PCB layout. Look at below! 4 Circuits.

Electronic siren circuits using 2 transistors

Operation of the circuit is Q1 and Q2 will work with R3, R4 and C2 is a frequency generator circuit with output connected to LED1 and speakers SP1. When I press the switch S1 to the C1 will begin to charge allows the voltage to pin B of Q1 increase other. The Q1 is working and Q2 is working with at the C1 charge full cycle will stop oscillator speaker is not.

The LED1 light and hold the release the pressure switch S1, resulting in C1 will start discharger through R3, Q1 to ground. The oscillator circuit sound Sirens in the lower out. If we press the switch S1 and then quickly leave many. The sound will be as continuous as C1 to charge and discharge alternately continuously.

Electronic siren circuit with two transistor

Parts will you need
Q1______2N3904,C1815,BC548,BC547,BC549,____45V 100mA NPN Transis_____________= 1 pcs.
Q2______2N3906,BC558,BC557,BC559,___45V 100mA PNP Transistor_________________= 1 pcs.
C1____________100uF 25V_____Electrolytic Capacitors__________________________= 1pcs.
C2_________0.1uF 50V___ceramic Capacitors___________________________________= 2 pcs.
R1__________47ohms_1/4W Resistors tolerance: 5%_______________________________= 1 pcs.
R2___________47K__1/4W Resistors tolerance: 5%_______________________________= 1 pcs.
R3___________33K___1/4W Resistors tolerance: 5%______________________________= 1 pcs.
R5,R6________68 ohms__1/4W Resistors tolerance: 5%___________________________= 2 pcs.
D1________1N4148____75V 150mA Diodes__________________________________________= 1 pcs.
SP1___________8 ohms 0.5W Speaker_____________________________________________= 1 pcs.
S1,S2_____Normally open pushbutton____________________________________________= 2 pcs.
And others,

This is simple circuit than upper.let’s build now!:)

Simple Siren by 2N2907 Transistor

This is simple siren circuit diagram that build easily. Because of use the transistor 2 pcs only just. Can use 8 ohm size loudspeakers. Which , I uses old loudspeaker , at the sound doesn’t Amen! come to usable with this comfortable circuit. The usability just you presses switch (close) S1 a loudspeaker will utter. Enhance the frequency goes up (C1 , loaded ). When liberate Switch(Open)S1. The sound will decrease the frequency down (C1 , disgorge load ) change the value R1. For change the time goes up – down. Please see circuit picture assembles.

Simple siren circuit diagram using 2N2907 Transistor

Parts will you need
Q1______2N2222____45V 100mA NPN Transis_____________________= 1 pcs.
Q2______2N29097___45V 100mA NPN Transistor___________________= 1 pcs.
C1____________22uF 25V_____Electrolytic Capacitors___________= 1pcs.
C2_________0.47uF 50V___Electrolytic Capacitors or ceramic Capacitors__________________________= 1 pcs.
R1__________39K_1/4W Resistors tolerance: 5%_______________________________= 1 pcs.
R2___________47K__1/4W Resistors tolerance: 5%_______________________________= 1 pcs.
R3___________22K___1/4W Resistors tolerance: 5%______________________________= 1 pcs.
SP1___________8 ohms 0.5W Speaker_____________________________________________= 1 pcs.
SW1________Normally open pushbutton__________________________________________= 1 pcs.

And others.

Ambulance sirens circuit

This is a sirens circuit that have sounds like of an ambulance sirens.It is different to the generally ambulance siren circuit.We use transistors instead of IC-555. Which
it save and easy to find all parts.

Operation of the circuit
This cycle can be divided into three main parts is the low frequency production. Production of high frequency. The amplifier.

The ambulance sirens  circuit
The schematic of Ambulance sirens

The manufacture low-frequency includes Q1, Q2, R2, R3, C2, C3. Which will produce low-frequency out and to extend the Q3. Before you sent with high frequency of origin from Q4, Q5, R8, R9. , C5, C6 signal is included, then the output will come out to the leg E of the Q5. and then be expanded with Q6(2N2222) to drive the speakers. The C1, C4 is intended to stir filter collects them. The R11 will help prevent speaker damage.

Transistor Q1-Q5, you can use very many number that is NPN 100mA current collector. For example :
2SC1815 or 2N2222 or 2N3904 etc.

Parts will you need
Q1-Q5______2N3904____45V 100mA NPN Transis_____________________= 5 pcs.
Q6______2N2222___45V 100mA NPN Transistor______________________= 1 pcs.
C1____________10uF 25V_____Electrolytic Capacitors___________= 1pcs.
C2,C3,C4_______1uF 25V______Electrolytic Capacitors___________= 2pcs.
C5,C6________0.04uF 50V___Ceramic Capacitors___________________= 2 pcs.
R1__________18K_1/4W Resistors tolerance: 5%_______________________________= 1 pcs.
R2,R3,R5________1.2M__1/4W Resistors tolerance: 5%___________________________= 3 pcs.
R6,R10___________10K___1/4W Resistors tolerance: 5%___________________________= 2 pcs.
R7_______________18K___1/4W Resistors tolerance: 5%___________________________= 1 pcs.
R8_______________12K___1/4W Resistors tolerance: 5%___________________________= 1 pcs.
R9_______________100K___1/4W Resistors tolerance: 5%__________________________= 1 pcs.
R11__________100 ohms___1/4W Resistors tolerance: 5%__________________________= 1 pcs.
SP1___________8 ohms 0.5W Speaker_____________________________________________= 1 pcs.
9V battery

And others.

American & Hong Kong police siren circuit using transistors

Today I suggest police siren circuit. Another circuit is very interesting. It can mimic the sound of a American police car and Hong Kong police. By which we use transistors mainly. For is so easy to buy equipment and budget.

How does it work.
In a Figure 1 will see that include of two sound generator set. First sound generator consist of Q1, Q2, C2, C3 and R1-R4. Then a second sound generator will include of Q3, Q4, C5, C6 and R7-R10. The sound signal will Different as level of parts in circuit.

Figure 1 The circuit diagram of a perfect American & Hong Kong police siren.

When a S2-switch is on “Hong Kong” position, the sound signal from a first series will out off from collector(C) of Q2 through R5 to controll working of the second sires. Which cause can get the output signal at collector of Q4 through R11 in to Q5 will be transformer-T1 by it is used to match the output of such circuits to a speaker.

If slide sw1 to “191” position will has also some sound signal through C4. A capacitance-C4 will cause feature of sound signal is changed.

How to build its.
You can assemble parts on the perforated board or universal board. But if you want to make PCB in permanent version. You can see in Figure 2 is actual-size of Single-sided Copper PCB layout. And Figure 3 is a components layout and wiring.
actual-size of Single-sided Copper PCB layout
Figure2 The Actual-size of Single-sided Copper PCB layout

components layout and wiring
Figure 3 The components layout and wiring

Application of this projects.
When assemble this project completely then to check for error, next apply the power supply 9-12volts, then test them by apply a 9-volts battery to the circuit. Next turn on power switch then press S2 we will hear a sound of siren from speaker anf LED1 flashes.

The applications can do many things. Such as be installed in the police car toy. Be installed on a motorcycle or a beep alarm for you.

The components list

Resistors ¼W +-5%
R1, R4, R7, R10—-1K ___________________ = 4 pcs.
R2, R3, R8, R9—–56K __________________ = 4 pcs.
R5——22K______________________________ = 1 pcs.
R6——560 ohms_________________________ = 1 pcs.
R11—–4.7K______________________________ = 1 pcs.
R12—–50 ohms___________________________= 1 pcs.
Q1-Q5——————C458 or similar (C1815 or C828)___= 5 pcs.

Polyester Capacitors 50V
C5, C6——————0.0047uF ______= 2 pcs.

Electrolytic capacitors

C1———————–220uF 16V ______________________= 1 pcs.
C2, C3——————3.3uF 16V _______________________= 1 pcs.
C4———————–33uF 16V ________________________= 1 pcs.
T1————-OT-601 ____Output transformer___________= 1 pcs.
S1, S3——– SPDT- Single-pole, Double-throw switch__= 1 pcs.
S2————-normally pushbuttom____________________= 1 pcs.
LED, speaker 8 ohms, PCB, Universal box.


  1. ekramul February 1, 2014
  2. ekramul February 1, 2014
  3. Roy Gonzales March 25, 2014
  4. Anthony Leija December 1, 2014
  5. momename December 2, 2014
  6. Dinesh August 26, 2016

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