design and construction of wailing alarm system (41 pages) CHAPTER 1-5

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design and construction of wailing alarm system (41 pages)


The wailing alarm system is an electronic device that can be used as a security purpose. It is an electronic wailing alarm, when install any body touches the wire cable, it sounds an alarm. The unit is built from discrete semi conductor device. It is relatively simple in both its operation and analysis. One particular feature of this project circuit (wailing alarm System) is its versatility. The circuit can be adapted for other applications. All the Information necessary for its realization is contained
in this project write-up. Chapter one contains the introduction to the wailing alarm system, Chapter two contains the circuit analysis and component review, Chapter three contains the research and methodology adopted, Chapter four contains the design and construction, while the work was concluded with Chapter five.


This circuit mainly consists of 555 timer IC. It has 8 pins. Sixth and second pins are shorted. Second pin is connected to ground through a capacitor of 10μ. 5th pin is connected to the ground through a 10μ capacitor for providing oscillations.

Switch is connected to 22K ohms resistor.
A 100μ capacitor is connected in series to the 100 Kohm resistors which is
connected to the base of the transistor. antenna is connected to the supply voltage
and emitter is connected to the supply voltage of 555 timer IC.
BC 547 is an NPN transistor. Initially, it is open circuited. When the based is
applied with some cut off voltage, NPN transistor starts conducting. In this circuit
BC547 transistor is used for driving the Speaker. Another NPN transistor BC557 is
used for providing supply to the 555 timer IC.

Here 555 timer is connected in as table mode. The 2nd and 6th pins are shorted to
provide continuous triggering of the circuit. Output pin of the 555 timer is
connected to the speaker through a transistor. Positive terminal of the speaker is
connected to the Supply voltage through a resistor.
Speaker used here is a 8ohms speaker. Internally, speaker will have voice coil,
diaphragm and attraction. When the electrical signals are applied to the voice coil
electromagnetic waves are generated around the coil and it interacts with the
magnetic field of the permanent magnet. Thus the permanent magnet and the
induced magnetic field repel and attract each other and thus producing the electric
signal changing its polarity. Thus the coil moves back and forth as a result of this
electric signal. This creates vibrations as the diaphragm moves continuously.
These vibrations are responsible for producing sound.

How Wailing Alarm System Works?

Initially power the circuit with a supply of 6v.
Now, press the switch S1.
One can observe the speaker producing wailing alarm sound.
The capacitor C1 starts charging and discharging to the supply pin of the 555 timer
IC as the transistor conducts when base voltage is reached.
When the 555 timer IC is applied with its supply voltage, the capacitor C1 starts

When it reaches 2/3rd of VCC capacitor starts discharging.
When this is at 1/3rd of VCC capacitor starts charging to produce the pulses.
As transistor is connected to the output, it is connected to the ground only when
transistor starts conducting.
And finally, speaker starts producing wailing sound.