This project presents a doorbell that alerts users when someone knocks on the door by playing a ringtone and illuminating an LED, without requiring wiring or drilling holes. The device uses a piezoelectric vibration sensor mounted on the door to detect knocks and convert the vibrations into an electrical signal. The signal is amplified and fed into a comparator circuit using an LM358 integrated circuit, with the sensitivity controlled by a potentiometer. When a knock exceeds the threshold, the comparator output triggers a buzzer to sound and notify the user of the knock. The device is powered by batteries and easier to install than a traditional doorbell.
2. Objective
The objective of this project is to build a
device with a vibration to electrical transducer
that alerts the user when somebody is at the
door. Unlike a traditional doorbell, this
doorbell plays a ring-tone when somebody
knocks at the door. It also illuminates an LED
to alert the user. It is easier to install than a
traditional doorbell because no holes need to
be drilled and no wiring needs to be done. The
user simply installs batteries and mounts the
device on their door.
3. Description of project
In this modern world everyone wants something new,
something different, so instead of using switch to ring the door
bell just an alarm is produced by knocking the door which
people feel more luxurious. The circuit of automatic alarm on
knocking uses a thin piezoelectric plate, senses the vibration
generated on knocking a surface (such as a door) to activate
the alarm and can also be used to safeguard motor vehicles.
The piezoelectric plate is used as the sensor. It consist IC
LM358 to which speaker is connected at the output.
Piezoelectric material is used at the input in order to convert
any mechanical vibration into electrical variation, it avoids false
triggering. The plate can be fixed on a door, cash box,
cupboard, etc using adhesive. A 1-1.5m long, shielded wire is
connected between the sensor plate and the input of the
circuit. The circuit operates off a 9V or a12V battery.
5. Working of project
The piezo drives a load resistor of 1M in parallel with a 5.1v Zener
diode just to protect the IC's against any large voltage spikes in the
event of a large physical bump. I found the raw output of the piezo
unsuitable for direct input to the Arduino as it is typically a very
small voltage signal and needs amplification, so I amplify the signal
from the piezo with a 221 gain non-inverting op-amp using one side
of an LM358. I use the other side of the LM358 for a comparator.
The sensitivity of the vibration sensor is controlled using a
potentiometer for the threshold (negative) input into the
comparator. The other (positive) input to the comparator comes
from the amplifier of the piezo signal. The output of the
comparator provides a direct input to Arduino Uno digital pin 8. To
hear when it senses vibration I use a simple piezo buzzer driven
directly from Arduino Uno pin 13.
7. Conclusion
Whenever a mechanical input is given as the input for
piezoelectric material those variations converted into
electrical variations and when it is interfaced with a
circuit which amplifies, rectifies, filters those signals
and buzzer is produced.
8. Future scope
1. Can be used as protective shield to the locker to avoid the
robbery.
2. Can be used as door bells
