The electronic doorbell in this article is
the most simplest among the advance projects in this website. There are
many other benefits of the project doorbell. The circuit for the
electronic doorbell here will help realise whether the visitor is in
front door or in back door. More about there is two LED indicatorwith
different colours which provide visual indication to check if anyone had
come nor not in your absence.
PART LIST
| T1,T2,T5 | BC148B |
| T3,T4 | BC158B |
| T6 | AC128 |
| D1,D2,D3,D4 | 1N4001 |
| D5 | GREEN LED |
| D6 | RED LED |
| C1,C2,C3 | 0.01 μF |
| R1,R7,R8.R9,R10 | 2.2 KΩ |
| R2 | 47Ω |
| R3,R4 | 100KΩ |
| R5,R6 | 10KΩ |
| R11,R12 | 330Ω |
| S1 | ON/OFF toggle switch for memory |
| S2,S3 | Switch for doorbell |
| BATT | 9-Volt Battery |
| LS | Loud Speaker 8Ω |
| OTHERS |
PCB , Connecting Wires, Hardware,enclosure etc |
Circuit Description
Working Principal
The presented circuit of doorbell in this
site is employs a direct couple complementary amplifier and two
regenerative latches. The working principal of the circuit doorbell is
simple. There are two switches S2 and S3 for FRONT and REAR door
respectively. The S1 is open the circuit act as a two-way doorbell. In
this case circuit act as a two-way doorbell with memory, that is the
audio alarm indicates whether the visitor is calling from the front door
or from back door.
When the S2 is pressed , diode D1 conducts
and the complementary amplifier built around transistors T5 and T6 .
Now T5 and T6 starts oscillating due to the positive feedback via
capacitor C1. In this case low frequency tone is produced which
indicates that visitor is a calling form front door. Similarly when
switch S3 is pressed then D2 conducts and a high frequency tone is
produced to indicate the visitor is calling at the rear door.
In your absence in someone come to your
home and call you then it will recorded in its memory. The circuit can
provide you an indication on return whether someone had come to your
house and called from front door or rear door.To use the memory unit of
this circuit you have to switch on the S1 which is the switch for
memory. After that whenever someone call you from front door or rear
door it will be indicated by the corresponding colour LED to the door.
The corresponding LED will be light up and remains in that state until
you return to your home. The Circuit can be reset by switching off the
memory switch S1.
When switch S1 in keep ON. This case if
someone come to your home and press the switch of front door that is S2
then diode D3 conducts through diode D5 and positive pulse is applied to
the base of the transistor T2. After that the regenerative pair built
around transistor T2 and T4 quickly full conduction and RED LED that is
D6 lights up and remains in that state until switch S1 is switch OFF.
In the same way when someone press the switch of rear door that is S3
diode D4 conducts through resistor R6 and a positive pulse is applied to
the base of the transistor T1 then the regenerative pair comprising
transistor T1 and T3 suddenly goes into full saturation and the D5 that
is GREEN LED lights up and remains in that stat until the memory switch
S1 in switched OFF.
If both the LEDs are found glowing on
returning from a visit then you may be surmise that the visitor(s)
called yo at the both the doors. In this circuit, diode D1 and D2 are
necessary to isolate the front switch S2 and the rear switch S3. In same
way D3 and D4 are used to isolate the audio section of this circuit
from regenerative latches. C2 and C3 are used to avoid false triggering
of the regenerative latches by the surge produced when S1 is switched
ON, as this is generally caused due to high gain of the transistors.
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