1. EC-329
SEMINAR
PPT
SUBMITTED TO : DR. SANDEEP SINGH
PRESENTED BY : SAKET BISHT
ROLL NUMBER : 20BEC023
SEMESTER : 6TH
BRANCH : ELECTRONICS AND COMMUNICATION
2. TABLE OF CONTENTS
• INTRODUCTION
• APPLICATION
• REQUIRED COMPONENTS
• WORKING LM35
• OP-AMP LM358
• WORKING OF RELAY
• WORKING EXPLANATION
• CIRCUIT DIAGRAM
3. TEMPERATURE
CONTROLLED
AUTOMATIC SWITCH
INTRODUCTION :
This is a circuit used in home A.C.
appliances to control the devices to
control them on basis of the surrounding
temperature. The circuit will serve as an
automatic light switch which will trigger
if temperature goes beyond a particular
level. The temperature sensor used in
this circuit is LM35. The threshold
temperature can be changed by changing
the value of the variable resistor.
4. APPLICATION :
In the circuit the threshold temperature is 30
degree Celsius. if the temperature goes above
30 degree the bulb in the circuit glows as the
switch is turned on. In contrast the switch
remains off if the temperature is below 30
degree and the bulb does not glow. The bulb in
circuit can be replaced by a fan or A.C. . One of
the other application of circuit is the fire alarm.
If the threshold temperature is increased to
very high value such as 100 degree Celsius it
can also work as fire alarm.
5. REQUIRED
COMPONENTS
• Battery (9V)
• IC 7805
• Temperature Sensor LM35
• OP-Amp LM358
• 10k ohm Resistor
• 1k ohm Resistor
• Variable Resistor 10k ohm
• LED
• NPN Transistor BCS547
• Diode 1N4007
• Relay (6V)
• Bulb or an A.C. appliance
7. WORKING :
TEMPRATURE SENSOR LM35:
• LM35 is a 3-pin transistor like device. It has a VCC, GND
and OUTPUT. The sensor provide variable voltage output
based on the temperature. The output provided by the
sensor is in degree Celsius up to 150 degrees. LM35 is an
inexpensive temperature sensor used in various digital
thermometers.
• For every 1 degree rise in temperature there is 10mV rise
in the output pin of the device. Hence, output will be 0mV
at 0 degree Celsius and will increase linearly with rise in
temperature at 30 degree Celsius it will have 300mV of as
output.
9. Now to set the reference
voltage, we must create a
Voltage Divider circuit by using
resistor RI and Variable resistor
RVI of 10k. By using the
formulae, we can set the
reference voltage accordingly
and can change the threshold
temperature. Eg. setting the 30-
degree Celsius temperature as
triggering value, we can set the
potentiometer roughly at 8.8k :
1.2k
10. Op-Amp LM358
LM358 is a Dual Low Noise
Operational Amplifier which has two
independent voltage comparators
inside. This is a general-purpose op
amp which can be configured in many
modes like comparator, integrator,
amplifier, differentiator, inverting
mode, non- inverting mode, etc.
Op-amps are also known as
Voltage Comparators. When voltage at
non-inverting input (+) is higher than
the voltage at inverting input then the
output of comparator is High. And if
the voltage of inverting input (-) is
Higher than non-inverting end (+),
then output is LOW.
11. WORKING OF RELAY
:
Relay is an electromagnetic
switch, which allows much
larger current to flow when a
small current is applied to it,
like we use transistor as a
switch. Relay is generally used
to control the AC (alternate
current) devices, using a much
smaller DC current.
12. Relay has a coil inside and when there is
no voltage applied to the coil, COM
(common) is connected to NC (normally
closed contact). And when there is some
voltage applied to the coil, the
electromagnetic field produced. Which
attract the Armature (lever connected to
spring), and COM and NO (normally
open contact) gets connected, which
allow larger current to flow. We are using
6V operating voltage relay, which allow
7A-250V AC current to flow.
13. WORKING
EXPLANATION
Working of this Temperature
Controlled Home Appliances Circuit is
simple, 9V general purpose battery is
used to power up the whole circuit and
IC7805 is used to provide the
regulated 5V supply to the circuit.
When temperature is below 30 degree
then output of LM358 remains LOW
and transistor Q1 & Relay also remain
in OFF state, thus bulb is off. We can
set this threshold temperature
accordingly by rotating the POT.
14. WORKING
EXPLANATION
Now when surrounding's temperature goes
beyond 30 Degree Celsius, output voltage of
LM35 at pin 2 also goes higher than 0.3 volt or
300mV. Output of LM35 is connected to Pin 3 of
Op-amp LM358. And as we have set the reference
voltage (voltage at Pin 2 of LM358) to 0.3 volt, so
now voltage at Pin 3 (non-inverting input)
becomes higher than voltage at Pin 2 (inverting
input) and output of op-amp LM358 (PIN I)
becomes HIGH. Output of LM358 is connected to
the base of NPN transistor Q1, so Q1 also becomes
ON which triggers the Relay and bulb gets turned
ON. Relay has small coil inside which get energies
by small current and trigger the AC device
connected to it. So that's how this circuit detects
the temperature limit and automatically switch on
the appliances.
