The document summarizes a student project on a light sensor circuit. It includes a list of group members, introduction to the concept of a light sensor using a light dependent resistor (LDR), circuit diagram, list of components including LDR, integrated circuit, variable resistor, resistance, transistor, diode, and relay. It describes how each component works and concludes with potential applications of the light sensor circuit including street lamps, alarm clocks, and burglar alarms.

1. Basic Electronics

2. Group Members
Names Roll Numbers
Mohsin Ijaz (Group Head) 110
Haziq Naeem 107
Hassan Riaz Khan 86
Muhammad Zohaib 136
Muhammad Adeel 83
Muhammad Naveed 120
Muhammad Ihsan 90
Class: BSCS-1C
Subject Teacher: Prof. Najaf

3. Project
Light Sensor

4. Introduction
Light sensor is a simple powerful concept. It
automatically switches ON lights when the sunlight
goes below the visible region of our eyes and
automatically switches OFF lights when Sunlight fall on
it (in morning), by using a sensor called LDR (Light
Dependent Resistor) which senses the light just like our
eyes.

5. Circuit Diagram

6. Components
• Light Dependent Resistor (LDR)
• Integrated Circuit (IC)
• Variable Resistor
• Resistance
• Transistor
• Diode
• Relay

7. Light Dependent Resistor
(LDR)
A photoresistor or light-dependent resistor (LDR)
or photocell is a light-controlled variable resistor. The
resistance of a photoresistor decreases with increasing
incident light intensity. In other words, it exhibits
photoconductivity. A photoresistor can be applied in
light-sensitive detector circuits, and light- and dark-
activated switching circuits.

8. Integrated Circuit (IC)
• An integrated circuit or monolithic integrated circuit
(also referred to as an IC, a chip, or a microchip) is
a set of electronic circuits on one small plate
("chip") of semiconductor material, normally silicon.
• Extremely small size, small weight, reduce cost,
extremely reliable, low power consumption, easy
replacement.
• IC Terminologies: Bonding, Chip, Diffusion mask,
Encapsulation, Etching

9. Variable Resistor
• The resistor whose electrical resistance value can
be adjusted as per requirement by adjustable
component attached to it is called variable resistor.
• Also known as port and potentiometer.
• A variable resistor is a strip of a material such as
graphite which resists the flow of electricity. There is
a fixed terminal attached to one end of the resistor.
There is also a moving device touching the graphite
called a wiper.

10. Resistance
• Resistance is the opposition that a substance offers
to the flow of electric current.
• The standard unit of resistance is the ohm.
• It is defined as the ratio of the voltage applied to
the electric current which flows through it:

11. Transistor
• A transistor is a semiconductor device used
to amplify and switch electronic signals
and electrical power. It is composed of
semiconductor material with at least three terminals
(Collector, Base and Emitter ) for connection to an
external circuit.
• Used in Digital and analogue switch, Signal
amplifier, Power regulator and equipment
controllers.

12. Diode
• A diode is a specialized electronic component with
two electrodes called the anode and the cathode.
• Most diodes are made
with semiconductor materials such as silicon,
germanium.
• It also work as switch.
• Diodes can be used as rectifiers, signal limiters,
voltage regulators, switches, signal modulators,
signal mixers, signal demodulators, and oscillators.

13. Relay
• A relay is an electrically operated switch.
• The advantage of using a relay is that a
small current can be used to
switch on and off a circuit with a large current .
• The output from IC is send to relays which results in
its excitation and gets activated.

14. • When the switch is closed, current flows
and the iron rocker arm attracted to
the electromagnet that
rotate and pushes the contacts
together.
• It may have a large current flowing
through it, to operate
a powerful motor or very bright lights.
• Used to control motors, heaters, lamps
or AC circuits which themselves can
draw a lot more electrical power.
Relay

15. Applications
o Street lamps
o Alarm clocks
o Home lawn and Parks
o Burglar alarms
o Camera light meters
o Light intensity meters