4 Simple transistor | police | ambulance Siren circuits

The siren circuits are what importance in the 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.

Simple transistor Police Ambulance Siren circuit

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 others.

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.

Simple Transistor Electronic siren circuit

Parts will you need

  • Q1: 2N3904,C1815,BC548,BC547,BC549, 45V 100mA NPN Transistor
  • Q2: 2N3906,BC558,BC557,BC559, 45V 100mA PNP Transistor
  • C1: 100uF 25V, Electrolytic Capacitors
  • C2: 0.1uF 50V, Ceramic Capacitors
  • R1: 47 ohms, 1/4W Resistors tolerance: 5%
  • R2: 47K, 1/4W Resistors tolerance: 5%
  • R3: 33K, 1/4W Resistors tolerance: 5%
  • R5, R6: 68 ohms, 1/4W Resistors tolerance: 5%
  • D1: 1N4148, 75V 150mA Diodes
  • SP1: 8 ohms 0.5W Speaker
  • S1, S2: Normally open pushbutton
  • And others,

This is a simple circuit than upper.let’s build now! 🙂

Simple Siren using 2N2907 Transistor

This is a simple siren circuit diagram that builds easily. Because of using the transistor 2 pcs only just.

We can use the 8-ohm size loudspeakers. Which, I use an old loudspeaker that not good for listening to music. But is so loudest for this.

The usability just you press the switch (close) S1 a loudspeaker will utter. Increase the frequency goes up (C1, loaded ). When liberating Switch(Open)S1.

The sound will decrease the frequency down (C1, disgorge load ) change the value R1. For a change, the time goes up-down.

Please see ะ้ำ circuit picture assembles.

Simple siren circuit diagram using 2N2907 Transistor

Parts will you need
Q1: 2N2222, 45V 100mA NPN Transistor
Q2: 2N29097, 45V 100mA NPN Transistor
C1: 22uF 25V, Electrolytic Capacitors
C2: 0.47uF 50V, Electrolytic Capacitors or ceramic Capacitors

0.25W Resistors tolerance: 5%
R1: 39K
R2: 47K
R3: 22K
SP1: 8 ohms 0.5W Speaker
SW1: Normally open pushbutton

And others.

Ambulance sirens circuit

This is a sirens circuit that has sounds like an ambulance siren. It is different from the general ambulance siren circuit. We use transistors instead of IC-555.

Which it saves and easy to find all parts.

Operation of the circuit

This cycle can be divided into three main parts is 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 the 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 numbers that is NPN 100mA current collector. For example :
2SC1815 or 2N2222 or 2N3904 etc.

Parts will you need
Q1-Q5: 2N3904_45V 100mA NPN Transistors
Q6: 2N2222, 45V 100mA NPN Transistors
C1: 10uF 25V, Electrolytic Capacitors
C2,C3,C4: 1uF 25V, Electrolytic Capacitors
C5,C6: 0.04uF 50V, Ceramic Capacitors
0.25W Resistors tolerance: 5%
R1: 18K
R2,R3,R5: 1.2M
R6, R10: 10K
R7: 18K
R8: 12K
R9: 100K
R11: 100 ohms
SP1: 8 ohms 0.5W Speaker
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 an American police car and the Hong Kong police. By which we use transistors mainly. For is so easy to buy equipment and budget.

How does it work?

In Figure 1 will see that include two sound generator set. The first sound generator consists 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 the level of parts in the circuit.

American police siren

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

When an 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 control the working of the second sires.

Which causes can get the output signal at the collector of Q4 through R11 into 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 have also some sound signal through C4. A capacitance-C4 will cause the feature of a sound signal is changed.

How to build it

actual-size of Single-sided Copper PCB layout

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 component’s layout and wiring.

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 assembling this project completely then to check for error, next apply the power supply 9-12volts, then test them by applying a 9-volt 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
R2, R3, R8, R9: 56K
R5: 22K
R6: 560 ohms
R11: 4.7K
R12: 50 ohms

Q1-Q5: 2SC458 or similar (2SC1815 or 2SC828)

Polyester Capacitors 50V
C5, C6: 0.0047uF 50V
Electrolytic capacitors
C1: 220uF 16V
C2, C3: 3.3uF 16V
C4: 33uF 16V
T1: TO-601, Output audio transformer
S1, S3: SPDT- Single-pole, Double-throw switch
S2: Normally pushbuttom
LED, speaker 8 ohms, PCB, Universal box.

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c547 ar poriborte ki use kora jai?


which transistor is replace to c547

Roy Gonzales

Please describe the Transformer specs shown in Figure 3. thanks…

Anthony Leija

Where are the real schematics for electronics I can’t find any can you help me Please i don’t trust too many schematics now days they don’t seem that they work 210-309-2078


How c2 is working ??


hi dear its very nice and helpful blog thanks for shairing

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