555 Siren sound Generator

A Sound Generator siren project, suitable for beginners. Build a simple, but widely applied.
The siren sound is a sound listening to indeed impactful. Commonly used as a sounds alarms in many forms. such as a burglar alarm in the house or install in car as alert sound ask to give way on ambulance, police car, or various recovery vehicles.
This projects is siren sound that sound effects like the siren of an ambulance or police car. Which features low-pitched tones alternately.
The working principle.
This project will be comprised of the oscillator circuits of 2 set. Using IC-555 timer IC are main both unit. The first oscillator serve determine time period in changing a high-low sound tone,provide the proper frequencies about 0.5-1 Hertz. Then, secoud oscillator set the siren sound, before out to a speaker.

In Figure 1 , The working of the circuit, Start from IC1 is installed as astable multivibrator to generate frequencies about 1 Hertz by R1 and C1 work together. Which generate the output frequency from IC1 is send through a R2-resistor to pin 5 of IC2. Which is a control voltage pin of IC1, will causes a tone that generate a oscillator at IC2 has pitched – bass sound as control voltage from output of IC1 there.
555 siren sound generator circuit

Figure 1 the 555 Siren sound Generator circuit

This second oscillator section have R3 and C2 together to set a frequency of siren tone pitched – bass as we want by increase or decrease C3. If increase it makes has low er tone and when decrease C3 cause has pitched up out to speaker.
The output from pin 3 of IC2, Usually can drive speakers directly. But it sounds sparse. Must be amplified by Q1 transistor. Which is a PNP transistor type, Rate of moderate power. May use another number instead. But I have to check and see if the leg is the same or not.
Transistors drive siren sound to speaker that will connect to circuit on the Common Collector. The connection on this form will causes maximum gain. The output on the emitter has low impedance. Making it possible to drive low impedance loads well. The output will be driven to the speaker, which is connected in series with R4-resistor, it is low resistance In the circuit is 4.7 ohms resistance rate was 1 watts. It can protect small speakers from damage in the event of a consecutive long.
If use speaker is a horn speaker with low power watts up to 5-10 watts or more. Do not need to put R4-resistor will cause the loudest up sound.
How to builds this projects
The Copper actual size as shown in Figure 2. Then put all components to PCB, do not forget to put the socket IC for both ICs to the convenience of plugged – remove them.The transistor gets warm during use but normal and when work continuously should install small heat sink.
The pcb layout of 555 siren sound generator

Figure 2 The PCB layout of the 555 Siren sound Generator
The components layout of the 555 siren sound generator

Figure 3 The components layout of the 555 Siren sound Generator
This projects can use the wide power supply, between 6V to 12V. High voltage makes more loudly. However, if the voltage changes. Will hear changed tones as well. If lower voltage to low frequency siren. If high voltage is higher tone siren. In the prototype 9-volt battery, a small rectangular blocks as a power supply circuit.
In case you want very siren. The speaker should use a small speaker horn. The sound will be even better.

Testing circuit.

After assembly is complete, try checking the device again. In particular, pin capacitor. If the wrong polarity, the circuit will not work at all (C1). Including the direction pin ICs. When finished, the power input to the circuit to hear the siren. Alternating high and low tone out of the the speaker.
If not satisfied, it can be changed,By changing the C1, which controls the speed. Fast or slow to change tone. And C2 is capacitor, control the siren tone to a high and low tone. as the need to try to change myself.
If it is used as a burglar alarm. They should find a box for it. The sensor is a switch, turn on-off power to the circuit. Placed sensors are as sensitive as a door or window. Your alarm system will be easy to use it.
The components List
Resistors ½ W + 5% (Unless specified.)
R4—————————–4.7ohm 1W
C1—————————–47uF 16V Electrolytic
C2—————————–0.0068uF 50V polyester
C3—————————–100uF 16V Electrolytic
Semiconductor devices.
IC1, IC2———————-IC-555 timer IC
Q1—————————-BD140 50V 1A PNP Transistor
Other devices.
SP1——-Speaker 8 ohms 0.25W size 2 inch
S1——–Rocker switch. NO/OFF (3pin)
B1——– Battery 9 volts with terminal
Socket IC 8 pin
PCB, Wire, etc.


You will also use many siren circuit that have IC-555 inside. see below:
1.Police sirens sound with ic 555
2.European police siren circuit
3.555 timer audio alarm circuits

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