The circuit I describe here a simple and cheap sirens of fire engines. The circuit is based on only 2 blocks: one oscillator (slow) and another oscillator (which is faster). Lock the pictures.
This circuit use only 14 components, all of easy acquisition and low price (here in Brazil at least) and can be mounted on a plate trial (which is what I did).
I will tell the story of this circuit. I made a whistle and acute with the 555 ci (which became the second block) and the following thought: if I on the other controlling the second IC 555, have a break in the whistle, thus swinging a whistle. But when you mount the circuit, realized that he played a voltage on pin 5 of IC 2 and change the swing of it! Thus the siren this project!
Step 1: building and modifying
The mounting plate in an experimental and easy to do through the scheme. Check all connections for which no errors. If you want a high-power siren, I suggest the following change in Figure 2. It was just that! Build your siren, modify it and improve it and publish your changes! until the next! Bye!