Here we are going to discuss about Touch sensitive siren Circuit. I hope you enjoyed my previous post about RF REMOTE CONTROL AND SWITCHING CIRCUIT.
As the Name of this circuit indicates, it is sensitive to our touch. The circuit will generate a siren, similar to police siren, when someone touch across the end terminals A and B. The circuit keeps ALARM as long as the touch.
You can even assign this circuit as a Burglar Alarm.
OrYou can try our Laser Based Burglar Alarm Circuit
The switching action is done under the principle of DARLINGTON PAIR. The darlington circuit triggers when someone touches across the terminals A and B.
The output Voltage from Darlington circuit is given directly to two 555 timer IC's (NE 555) which is wired as astable multivibrator and the output from first timer is cascaded into second one. The rise and fall Voltage of both the ICs drive the buzzer, hence a tone similar to police siren.
The Transistors Q1 and Q2 forms Darlington Pair, you can use any common type NPN Transistors such as BC548, BC107.....