The noise or vibration activated alarm circuit displayed in this article makes use of its pre-installed loudspeaker like a microphone while it is within the sland- by-state.
How the Circuits Works
The moment it picks up a noise that surpasses an adjustable tolerance point. it gets activated. This little. smart circuil may be used as an security alarm generator which responds to disturbances.
You may also put it to use to help you identify a physical object according to a noisy sound such as clapping both hands or whizzing noisally. The gate at the end of the schematic diagram works like a linear low-frequency ampliﬁer because of the negative feedback resistor R3.
It obtains its input signal from loudspeaker LSI. that functions as a microphone whenever T1 is cut off. The ampliﬁed output signal through this gate goes by through Cl to a second IC 4011 gate which activates a monostable established by the a couple of gates positioned before & after CS and R5.
The DC threshold amount is put on pin 2 of IC1 via R2. This DC voltage is superimposed within the signal coming from Cl. Retriggering of the monostabie is averted by the collaboration of R4, C4 and thc first gate, additionally on which the sound generator IC1d stops the loudspeaker from behaving as a microphone as soon as it has been triggered.
A High output signal through pin 4 of the monostable makes it possible for a couple of astable multivibrators in IC2.
The first of these is a low-frequency generator which modulates the audio frequency tone generated by the second multivibrator. In this way a ‘siren' type of shrillsound that is heard from the loudspeaker. Ultimately Tl is powered via R8 to exert the loudspeaker pretty hard.
The loudspeaker current is restricted slightly little bit by R9. The length of the alarm signal depends upon the monostable time constant of R5 and C5. A Low logic on pin 4 of ICI obstructs the sound generator. Following the time delay established by R4 and C4 has ended. the loud-speaker yet again works like a microphone. The circuit could be driven with a 5 V to 9 V battery.
Circuit Diagram for the above Explained Vibration Activated Alarm Circuit