Hey Geeks! Welcome to The Engineering Projects. We hope you are having a reproductive day. We know that sirens are the special sounds that are the symbol that something unusual is occurring or about to occur. You may have experienced the Siren of the Walkthrough Gates at the airport when a person having the knife or other forbidden material pass through it. Or you have heard the Siren of the ambulance and seen that all the traffic gives the way to the ambulance when they hear the special Siren of the Ambulance. The same is the case with the police Siren. The Police sirens are the special sound and it is set with the help of 555 Timer Integrated Circuit. You will learn how can one design a Police siren using the 555 Timer circuit in this tutorial. Let's have a quick list of the topics that will be clear in our tutorial.
1. What is the 555 Timer Police Siren?
2. What are the 555 Timer and its modes?
3. How does the circuit of 555 Timer police Timer Circuit works?
4. How can you design the circuit of 555 Timer Police Siren in Proteus?

## 555 Timer Police Siren

The Police Siren we have seen many times in real life as well as in Television shows and Movies are made of the special arrangement of the 555 Timer. The Siren has a loud voice that can be heard at a distance of many feet. This Project has a very simple yet amazing arrangement of some basic electronic devices. The heart of Police Siren is the 555 Timer integrated circuit. In the police siren, two 555 timers are used. This is a Multi-functional chip that is widely used in different types of the industrial as well as household applications. If we look at the configuration of 555 Timer Integrated Circuit then we can generate a table just as shown next:
 Pin Number Attachments 1 Ground 2 Trigger 3 Output 4 Reset 5 Control 6 Threshold 7 Discharge 8 Vcc
Technically, The 555 Timer works in 3 modes:
• Monostable Mode
• Astable Mode
• Multistable Mode

### Monostable Multivibrator Mode in 555 Timer

This mode of the 555 Timer contains a single stable state that can be used to get only one single output pulse of a specific width that may be high or low by applying an external trigger pulse. In this circuit, the 555 Timer uses only one resistor but two capacitors.

### Astable Mode in 555 Timer

As the name shows, the Astable mode does not have any stable state. The Astable mode of 555 Timer has 2 quasi-steady states that change from one state to another one after the other. In this way, the 555 Timer in this state, alters the output from high to low and vise versa after the time settled by the user. It uses two capacitors and two resistors connected with the specific pins in a specific manner.

### Bistable Mode of 555 Timer

In this mode of 555 Timer, the pins are connected with two resistors, one capacitor and two switches. The switches turn the state of 555 Timer to high and low and thus we obtained the high and low output waves at a time.

## Working of the 555 Timer Police Siren

The working of the 555 Timer Police Siren starts from the Direct Current power supply that is supplied to pins 8 of the 555 Timer.
1. Both of these 555 Timers are in the Astable mode that means their pulse output changes continuously.
2. The 555 Timer at the left produces a pulse that is fed into the right 555 Timer as an input.
3. The values of Resistors control the width of the pulses.
4. The capacitors connected with the 555 Timers charge and discharge without any interval.
5.  At the end, this DC power supply enters the speaker with a continuously varying pulses of the current and produces a special sound.
6. If you want to change the output voice, you can change the values of Resistors and capacitors.

## Circuit design of 555 Timer Police Siren in Proteus

To design this circuit, simply follow these step given next as it is.
• Start the Proteus Software.
• Choose the required devices from the pick library by clicking the "P" button and writing the names of the devices.

### Required Components fpr 555 Timer Police Siren:

1. NE555 Timer (We'll use 2 ICs)
2. Diode
3. Resistor
4. Direct current power supply
5. Speaker
6. Capacitor
• Get the 555 Timer from the library and arrange it at the working area.
• Repeat the step above.
• Choose Resistor, capacitor, Diode and speaker and arrange them on the screen.
• Change the alignment of 4 resistors and diode by left click on screen> Rotate Clockwise and set the whole circuit as shown in the figure:
• Go to Generation Mode>DC and fix it at above the working area.

### DID YOU KNOW ???

"If you have the Proteus 8 software, then you can have a real time Siren sound by choosing the Speaker and a piano symbol with it."
• Label the Components by double-clicking it because Proteus throws an error for the duplicate devices.
• Double click the components mentioned below and change their values according to the table given next:
 Device Value R2 68k Ohm R3 68K Ohm R4 8.2K Ohm R5 8.2K Ohm C1 100uF C2 100nF C3 0.01uF C4 10uF Vcc 4V

• Go to Terminal Mode>Ground and Set the Ground terminal just below the circuit.
•  Join the 555 Timer's pins with the components as described above in the 555 Timer section.
• Pop the Play button and simulate the circuit.