In this tutorial you will build a wailing siren that plays a tone that increases and decreases in pitch. The circuit is built from two 555 timer ICs and some additional electronic components. The wailing tone is played on a loudspeaker.
A Wailing Siren Circuit that uses Two 555 Timer ICs
can u please tell me the use of the diode and transistor in the wailing siren circuit?In what mode is the transistor working?is the transistor working as a switch or as an amplifier?It will be very good if you provide me the working and utility of each component used in the entire circuit
Hi Pooja
The diode in the circuit is to make the first 555 IC output a waveform that has a 50% duty cycle. The transistor is operating as a buffer amplifier with unity gain.
The 555 timer on the left in the circuit diagram is oscillating slowly. It then increases and decreases the frequency of the second 555 timer to produce the wailing sound.
The two 555 timer circuits are standard 555 oscillator circuits, except the second IC allows the first IC to change its oscillator frequency between an upper and lower value.
Okay i did everything dead on to the diagram but its only letting out a really low sound Would you know where i messed up at?
Never mind about the last question Turns out my power supply wasnt hooked up right x.x Great tutorial btw
Ok, glad you enjoyed the tutorial 🙂
Hi, I designed the circuit using Ltspice but I don’t seem to find the speaker symbol in the Ltspice library. Pls how do I rectify this problem…
I’ve got it wiired up correctly, verified with diagram AND the image. I’m unable to get anything to work. All caps and resistors test out fine. Swapped out transistor. Using a 9v battery and known good/tested speaker and swapped out the 555s. I just can’t get this one going.
Scratch that last comment. Learned that I needed to connect the whole length of the + and – rails of the bread board. Didn’t realize that it was split in the middle. Still a little green in my electronics quest.
Thanks for your feedback, your comments may help others who are having a problem. You can see a comparison of two different types of breadboards here: http://startingelectronics.org/reviews/tools/arduino-breadboard-review-a000032/
There is a photo towards the end of the article that shows the different power rails – one connects straight through and the other is split.