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1. DIGITAL ELECTRONICS LAB
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Student Name: MILAN
UID: 21BCS4362
Date of Performance: 18-02-2022
Branch: BE-CSE
Section/Group: 211-A
Subject Name: Digital Electronics
 AIM -
1. Design a Burglar alarm using AND gate such that the alarm should turn on
whenever light falling on the LDR is disrupted.
2. Design a voting system such that a valid vote will be considered when a
personsitting at a desk presses boththe buttons. IN case only one button is
pressed during the casting of the vote the votewill be considered as invalid.
Also a valid casted vote will be represented by green light and invalid
casted vote will be represented by a red light.
3. Design an automatic heater controller using NOT gate such that at
temperature below 10oC the heater should turn ON (the heater can be
represented by using an LED).
 Requirements - 7404 (NOT) IC, 7408 (AND) IC, 7432 (OR) IC, 5V
Power Supply, Breadboard, Connecting wires, Simulation software,
Windows 10 PC
 Theory –
(a)Burglar Alarm using AND gate
An AND gate gives an output of logic 1 when input A AND input B are at logic
1, i.e., when the alarm switch is ON and the LDR sensordetects a light (flashlight
that burglar uses), only then the Alarm will ring, otherwise, it will not ring in any
of the other cases.AND gates are available in IC packages. The 7408 IC is a well-
known QUAD 2-Input AND gates IC and contains four independent gates each
of which performs the logic AND function.
In order to design the burglar alarm, the alarm switch which is a SPST (toggle)
switch and the person detection is achieved by the light falling on the sensor (
because of the light source used by the burglar) made from LDR, is used. The
schematic of the circuit is shown as below.

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 Circuit Diagram :
 Tinkercad Simulation :

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(b) Single doorbell ringer for both front and back doors, using OR
gate.
The Logic OR Gate is a type of digital logic circuit whose output goes HIGH to
a logic level 1 only when one or more of its inputs are HIGH. It is required that
the doorbellshould ring when someone presses either the front doorswitch or the
back doorswitch. OR gates are available in IC packages. The 7432 IC is a well-
known QUAD 2-Input OR gates IC and contains four independent gates each of
which performs the logic OR function.
In order to implement the doorbell ringer, the SPST (toggle) switches are used as
inputs to the OR gate, the output of the OR gate is attached to a Buzzer which
will ring when any one of the switches is pressed.
 Circuit Diagram :
 Tinkercad Simulation :

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(c) Designan automatic fan controller(NOT).
The Logic NOT Gate is the most basic of all the logic gates and is often referred
to as an Inverting Buffer orsimply an Inverter. It is required to controlthe central
heating to turn on/off according to the temperature threshold. The temperature is
sensed by the LM-35 temperature sensor having a linear relation of the output
voltage to the temperature by 10mV/oC. The decision ofthis temperature is above
or below a threshold temperature is taken by OP Amp working as a comparator.
Since the relation is linear we know this that at 30 oC the output of LM-35 must
be 300mV so we will make Vref of Op-Amp as 300mV.
If the temperature at –ve terminal or Op-AMP is above 30oC then voltage output
of LM-35 will be greater than 300mV and output will be 0V which will act as
logic LOW at the input of NOT gate and in return, it will give logic HIGH at
output turning the fan ON.

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Whereas, if the temperature at –ve terminal or Op-AMP is below 30 oC then
voltage output of LM-35 will be less than 300mV and output will be 5V which
will act as a logic HIGH at the input of NOT gate and in return, it will give logic
LOW at output turning the fan OFF.
Each 7404 NOT gate IC has 6 NOT gates arranged as shown in Fig 12. 14th pin
is the VCC (+5V) and the 7th pin is the GND (Ground). In order to implement
the experiment, the temp sensor input needs to be given to the input terminal of
any one of the NOT gate inside this IC, and the output actuator can be driven
from the output terminal of the same gate.
 Circuit Diagram:
 TinkercadSimulation:

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 Result :
The integrated circuits and their connections on the breadboard were studied
and implemented. The practical applications of logic gates (AND, OR & NOT)
were studied and implemented.