Alarm controlled by noise
Cercle de trois / BA306

This project can be called a stretcher noise or alarm controlled by noise. The noise detector (earphone operating as a microphone) has to be hit or has to receive a brief pulse noise and the speaker heard a noise. If you place the speakers too close to the earphone, resulting in sustained oscillations.

This circuit could be used as anti-theft alarm with the earphone where it could be bumped if someone tried to move or take something. The resulting roar attract attention and probably scare the thief.

The circuit operates by the signal amplification by the Circle of three, the rectification of the signal by the diode to germanium (Ge) and by applying the CC as resulting base bias to the PNP oscillator.

The oscillations of the PNP are always stronger and longer than the noise or speech necessary to put the oscillations running. This is because of the charge storage capacitor action of 3.3 uF.

Try to place the system near a device that can make a noise like a stereo, high-fidelity loudspeaker, without telling anyone. Then, watch the faces when noise is added to what they expect to hear.

Do you have a barking dog? This perhaps make a little more careful before yelping because of this machine that makes fun of him.

Have fun!

This assembly is the last sound oscillator with for some time. It would be good to spend your notes reviewed. What have you learned on the oscillators far? Have you managed to create yourself interesting hardware?

Try to build your zoo and your electronics factory sounds as we have done here. Here is a major objective therefore try to mount your own sound oscillator with your notes and knowledge you have acquired so far. We think you can do it. (Even if you do not succeed, you begin to create electronic circuits as we had promised you!)