Electronic Siren 1
Don't be surprised if this becomes the most popular circuit!
This circuit sounds so much like a real siren used on some police cars and ambulances you may have to modify the circuit or risk being arrested for impersonating a police car! (Don't worry...we're just kidding). Some of the modifications you will want to try are listed below:
1. Change the 10uF to a 100 or 470uF. This gives a very long delay for both turn-ON and turn-OFF.
2. Change the circuit to eliminate the ON-OFF delays by replacing the 10uF with an open circuit. (Sounds dead in comparison doesn't it!)
3. Change the 0.02uF to a 0.01 and then a 0.05.
You should be able to determine how this circuit works by comparing it to the circuit of project Pulse Oscillator Tone Generator in Oscillator Section.
Actually the changes are few so if you use the same method of following the currents around you can do it. Start by considering this circuit without the 10uF Capacitor. Without this component the operating characteristics are virtually identical to the other project.
After obtaining an understanding without the 10uF, try including it in your analysis. Remember, with the 10uF in the circuit the turn-ON and the turn-OFF are delayed.
Here is another version