Police Siren Circuit Using 555 IC

A tutorial on how to make a police siren circuit using 555 timer IC and a few other electronics components. This circuit smoothly transitions the output sound between two different tones/frequencies, similar to the sound emitted from police cars.

You can also club this circuit with police lights circuit, which is the previous project in this 555 timer projects series: Police Lights Themed Flashing LED Circuit Using 555 IC.

Components Required

  • 2 x 555 Timer IC
  • 8Ω Speaker
  • Resistors: 100K, 33K, 2 x 1K, 2 x 10K
  • Capacitors: 1000uF, 100uF, 10uF, 100nF
  • Breadboard
  • Few Breadboard Connectors
  • (5-9)V Power Supply

Circuit Diagram


How This Circuit Works

[Watch the explanation provided in the video tutorial for better visual understanding]

In the electronic piano circuit we built in one of the previous projects, we are able to generate different output tones by using different resistor combinations. You may refer to that tutorial for better understanding of how this circuit works: DIY Electric Piano Circuit using 555 timer IC.

Here we have used a similar arrangement using astable mode of 555 timer IC to produce a single tone. But in order to mimic police siren sound, we need to transition to and fro between 2 tones or frequencies.

And this transition between two tones is made possible by using a second 555 timer IC in astable mode and by connecting it’s output to control pin of the first 555 timer IC. Now depending on the output state of the first 555 timer IC, we get 2 different frequencies from the second 555 timer IC.

Because of the 1000uF capacitor, the voltage at the control pin increases and decreases gradually instead of a sharp rise and drop. And as a result we get a smooth output that oscillates between 2 tones similar to a police siren.

If you have any queries/suggestions, feel free to post them in the comments section of this video: Police Siren Circuit Using 555 IC