A Siren


This project describes a circuit for a siren. IC 555 is used so that the circuit components are low cost and available off the shelf. Two 555 ics are used. One of them is modulating frequency oscillator the other is modulated frequency oscillator. Note the connection between the two ICs. Instead of the rectifier and the filtered power supply, you can use a 9V battery.



Modulating oscillator

This produces low frequency. With this frequency, the high frequency oscillator is modulated. The components are selected such that,

  • Its frequency is 0.577 Hz.
  • Duty cycle is 0.6.
  • Period is 1.732 sec.

Modulated oscillator

The oscillator oscillates with,

  • 577 Hz
  • Duty cycle is 0.6 and
  • Period is 0.00173 sec.

The loudspeaker

8 ohm speaker with paper cone (nearly 4 cm diameter) is used.

Material list


Sr. No. Component Specifications Quantity
1 diode 1N4007 4
2 filter capacitor 1000mfd/16V 1
3 transformer 230V/9V,300mA 1
4 IC 555 standard 2
5 disc capacitor 0.1mfd 2
6 electrolytic capacitor 100mfd/25V 1
7 resistors 5k,10k (0.25W) 2 each
8 resistors 3k3(0.25W) 1
9 transistor SL100 1
10 speaker 8 Ohm, 4cm dia 1
11 pcb General purpose, 4″ X 4″ 1
12 misc solder metal,wires
13 battery 9V, flat,non rechargeable 1

 Note: You can eliminate the rectifier (diodes) and filter (1000mfd capacitor) components from the above list if you use a 9V flat battery.

This project is available in the kit form. Contact Omkar to buy it. This site has no commercial connection with his activities.

तुमचे मत नोंदवा

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  बदला )

Twitter picture

You are commenting using your Twitter account. Log Out /  बदला )

Facebook photo

You are commenting using your Facebook account. Log Out /  बदला )

Connecting to %s

%d bloggers like this: