This is a full Project Report with Demonstration available for measurement of Electric Current for Measurement and Instrument students, for a brief Idea and source for "How to Approach" for an LDR Experiment.

1. EEE – 2004
Measurement and Instrumentation
Measuring the amount of current drawn by a load in LDR circuit when in light vs in darkness
Name : Sumit Dutta | Registration Number : 20BEE0354 | Slot : G1

2. 1. Abstract
2. Introduction
3. Materials Required
4. Principle
5. Circuit Diagram
6. Working of the Circuit
7. Functioning, Cost and
Application of the Model
8. Observation Table
9. Reference

3. Majority of street lights,
outdoor lights, and a
number of indoor home
appliances are typically
operated and maintained
manually in many
occasions. This is not only
risky, however additionally
it leads to wastage of
power with the negligence
of personnel or
uncommon circumstances
in controlling these electrical appliances ON and
OFF. Hence, we can utilize the light sensor circuit for
automatic switch OFF the loads based on daylight’s
intensity by employing a light sensor.

4. What is a Light Dependent Resistor ?
An LDR or light dependent resistor is also
known as photo resistor, photocell,
photoconductor. It is a one type of resistor
whose resistance varies depending on the
amount of light falling on its surface. When
the light falls on the resistor, then the
resistance changes. These resistors are
often used in many circuits where it is
required to sense the presence of light.
These resistors have a variety of functions
and resistance. For instance, when the LDR
is in darkness, then it can be used to turn ON
a light or to turn OFF a light when it is in the
light. A typical light dependent resistor has a
resistance in the darkness of 1 MΩ, and in the
brightness a resistance of a couple of KΩ.

5. Materials Required
a 12 mm
LDR
element
The following materials and
components were used in building this
project, with accuracy and success :
1. Breadboard
2. Alpins
3. 2-Pin wire
4. 12V, 2A LED driver
5. Ammeter
6. One 50 kΩ and one 1 kΩ resistor each
7. Red PVC tape
8. One BC547 transistor
9. One 12 mm LDR element
10. Four jumper wires
11. 12V LED cable light without switch
12. One diffused 5 mm orange LED bulb
13. A well levelled ground to demonstrate
14. Gloves for safety
15. Video camera for demonstration

6. The working principle of an LDR is photoconductivity,
which is nothing but an optical phenomenon. When
the light is absorbed by the material then the
conductivity of the material enhances. When the light
falls on the LDR, then the electrons in the valence
band of the material are eager to the conduction
band. But, the photons in the incident light must have
energy superior to the bandgap of the material to
make the electrons jump from one band to another
band (valance to conduction).
Hence, when light having ample energy, more
electrons are excited to the conduction band
which grades in a large number of charge
carriers. When the effect of this process and
the flow of the current starts flowing more,
the resistance of the device decreases.
Principle of a LDR Circuit

7. Circuit Diagram
Design
©
Sumit

8. Circuit Working
Abiding by the principle on which the said model of
indicator works, the working mechanism of this LDR
circuit is very simple, lucid and easy to understand. This
works, only whenever there is a dim in the intensity of the
light falling on the Calcium Sulphide track of LDR, the LED
component attached show an increase in it’s brightness
and an ammeter also shoes the current amount with
maximum of these at complete darkness and negligible
when under full bright light. In the beginning, we connect
the two resistors in parallel combination with the 2A LED
driver, which is used for recognizable current reading in
the ammeter. The LDR is connected with the 50 kΩ
resistor in series, whereas the load component along
with ammeter and collector of the BJT is in series with 1
kΩ. The Circuit gets completed when, the base of the BJT
is Connected to the LDR and further the LDR and emitter
of BJT is connected with the neutral of LED driver. With
the above explained connections being done, when a final

9. connection of the 2-Pin plug with the LED driver is switched on
with mains, under bright conditions, no change is observed either
in the connected bulb or the ammeter but, on trying to hover a
piece of cardboard or a hand over the LDR, makes us observe that
light starts to glow for the duration of hovering. On trying to
completely switch off all the lights, the bulb glows at it’s maximum,
which would again diminish if we turn on the lights again.
The working behind this set-up is because the LDR is a kind of variable
resistor as per the situation. At the time of external lights being
switched on, the resistance of the LDR is at it’s minimum, due to which
all the current enters 50 kΩ resistor, such that the overall resistance
experienced is less enough than the other laid parallel branch headed
by 1 kΩ. As soon as the lights starts to turn off, the resistance
increases and it is drastic at complete darkness, due to which the
incoming current now finds, the other branch with lesser resistance
offered to flow. Moreover, collector current gets multiplied β times the
current entering the base region, which makes more evident as to why
the bulb glows brighter than the same amount of current received
would glow much times less bright if this was another ordinary circuit
with an ammeter showing 11.5 mA. The BJT helping the set-up to make
the bulb glow brighter in darker conditions, the current exits from the
emitter terminal back to where it emerged from the LED driver,
making the circuit complete with it’s purpose fulfilled. Until the mains
are kept on, this working purpose is expected to continue on.

10. Functioning of the Model
Total Cost of Involved
Application in Practical Life
LDR circuits are useful as street lights, mining lamps,
alarm clocks, light intensity meters, burglar alarm
circuits, infrared astronomy, smoke detectors,
photosensitive relay, optical coding, camera light
meters, security alarm, light activated control circuits
and are used as a proximity switch and into automatic
contrast and brightness control in television receivers.
The total cost for each and every component
as shown into the video demonstration, cost
me ₹2070, from various web stores around.
https://youtu.be/yWCd18c6LIU
Video Image and Link

11. Observation Table
Type of Load
Connected
Ammeter
Reading
All the
components 2 mA
Blue cabin light
LED 3.5 mA
Orange 5 mm
LED 9.5 mA
Only Ammeter
11.5 mA

12. Reference
https://www.youtube.com/w
atch?v=jqHOPSL2MMU&t=64s