A tutorial on how to make a wailing siren circuit using 555 timer IC on a breadboard. This circuit can be triggered by pressing a push button switch and it produces a tone with increasing intensity for as long as push button is pressed. After the push button is released, the intensity of siren sound gradually reduces to zero.
- 555 timer IC
- 8 Ohm Speaker
- Transistors: 1 BC547, 1 BC557
- Momentary Push Button Switch
- Capacitors: 10nF, 100uF
- Resistors: 39R, 22K, 33K, 100K, 2 * 220K
- Few Breadboard Connectors
- (5-9)V of Power Supply
How This Circuit Works
In the previous project: DIY Electric Piano Circuit using 555 timer IC, we have created tones with different frequencies using astable mode of 555 timer IC. You may refer to that tutorial for better understanding of how this circuit works.
At the core of this circuit is a similar astable arrangement that produces sound with fixed frequency. In addition, a PNP transistor is used to power the 555 timer IC. So the intensity of output sound depends on the amount of current supplied by this transistor to 555 timer IC.
Negative voltage at the base pin of PNP transistor will cause the transistor to allow maximum current to flow through 555 timer IC which results in louder sound and vice versa.
We utilized this behaviour along with capacitor-resistor arrangement to gradually increase and decrease the current flowing through 555 timer IC, while taking into account the duration for which push button is pressed. As a result, the intensity of siren sound gradually increases and then decreases to silence.
Please go through explanation section of the video tutorial for better visual understanding.
If you have any queries/suggestions, feel free to post them in the comments section of this video: Wailing Siren Circuit Using 555 IC