Police Siren Circuit on Power Breadboard PBB-272B

A tutorial on how to make a police siren circuit using 555 timer IC on our famous Power Breadboard PBB-272B. This circuit smoothly transitions the output sound between two different tones/frequencies, similar to the sound emitted from police cars.

Table of Content.

1. Part List
2. Circuit Diagram
3. How does this circuit work?
4. Conclusion

Part List

• 2 x 555 Timer IC
• 8Ω Speaker
• Resistors: 100K, 33K, 2 x 1.1K, 2 x 10K
• Capacitors: 1000uF, 100uF, 10uF, 100nF
• Power Breadboard PBB-272B
• Jumper Wires

Circuit Diagram

How This Circuit Works

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. By connecting its output to the 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.

Please watch the working system here. https://youtube.com/shorts/0uvXcoO5g-s

Conclusion

Changing the value of the resistor in series with the capacitor changes the flashing rate (frequency). This type of system is well suited for an analog circuit with a 555 timer, it would not be simple if one tries to use a microcontroller since the microcontroller then needs to output a specific frequency depending on the position of a potentiometer, which could be a nightmare for programmers.