Police Siren Using 555 Timer

Police Siren Using 555 Timer

Police Siren using 555 timer is a very interesting project for DAE or Engineering students. In this project we will produce the out signal which produce the sound like police siren. 

In this Project we are using very basic and simple components like as 

1. Two 555 timer ICs 
2. Some resistors values are mentioned on diagram
3. Capacitors
4. Simple diode 1N4001
5. One Pot-meter 5K
6. Buzzer
7. 9v battery 

• 555 Timer

555 timer belongs to the category of mixed ICs means digital and analog. 555 timer internal circuit is cconsist on two Op-Amp Comparators and one RS latch and three 5k resister network. Physical shape, internal circuit and Pin out of the IC is as under.

• Internal circuit:

• Pin Out:

• Pins Description:

1.       Ground
2.    Trigger: In case of 555 as MMV we apply trigger pulse at this pin to unstable the output of                  MMV.
3.     Output
4.     Reset: Pin#4 is mostly on +v when we want to reset the MV then we apply 0 level on this pin.
5.     Control Voltage: In case of 555 timer VCO(voltage control oscillator) variable voltage applied          on this pin to vary the output frequency.
6.     Thresh Hold: At this pin an external capacitor connected to change the output by charging and          discharging.
7.     Discharging: This pin provides the short path to external capacitor for discharging.
8.     +Vcc

• Circuit Diagram:

In above Diagram (which is the simulation view of Livewire you can simulate it in proteus as wel) IC1 timer IC is behaving as AMV (Astable Multi-Vibrator) and 2nd one is behaving as VCO (Voltage Control Oscillator). AMV is just making voltage out put high and low and VCO out put frequency changing according to AMV voltages up down. So when Out1 will high then Out2 frequency go down and when Out1 voltages goes to zero then Out2 frequency go high. Accroding to this frequency variations Buzzer produce sound like Police Siren. look at wave form.