LDR-experimentation.pdf pg. 1 COVENTRY UNIVERSITY Faculty Of Engineering & Computing AAEE Light Depended Resistors (LDRs) Introduction The light dependent resistor, LDR, is known by many other names such as photoresistor, photoconductor, photoconductive cell, or simply the photocell. These devices were discovered by an English electrical engineer Willoughby Smith back in 1873. Smith’s main line of work in 1848 was the laying of underwater telegraph cables. He developed a method of testing an underwater cable as it was being laid. One of the insulation materials used for the cable was selenium. Upon investigation of the properties of the selenium insulator he discovered that the conductivity properties of the material were affected by light. He published his findings in 1873. Since then many variants of photoconductive devices have been made. Other LDRs have been made using materials including cadmium sulphide, lead sulphide, and the more commonly used semiconductor materials including germanium, silicon and gallium arsenide. The most popular material used in making LDRs is cadmium sulphide (CdS). The LDR finds many uses as a low cost photo sensitive element and was used for many years in photographic light meters as well as in other applications such as lighting controls for street lamps etc. Basic structure of an LDR There are many ways in which light dependent resistors can be manufactured. Essentially the LDR consists of a resistive material sensitive to light. The photo resistive element comprises section of the material with contacts at either end. Although many of the materials used for light dependent resistors are semiconductors, when used as a photo resistor, they are used only as a resistive and they are purely passive. A typical structure for a light dependent or photo resistor uses an active semiconductor layer that is deposited on an insulating substrate. The semiconductor is normally lightly doped to enable it to have the required level of conductivity. Contacts are then placed either side of the exposed area. Fig 1 (a,b,c) Close-Up of an LDR (a) Cadmium sulphate (b) and LDR symbol (c) (a) (b) (c) pg. 2 In many instances the area between the contacts is in the form of a zig zag, or interdigital pattern. This maximises the exposed area and by keeping the distance between the contacts small it enhances the gain (see Fig.1 (a). Although other devices such as photodiodes or photo-transistors can also be used for light sensing applications, LDRs are a particularly convenient electronic component to use. They provide large change in resistance for changes in light level. They are of comparatively speaking of a lower cost as compared to other light responding devices. How an LDR works It is relatively easy to understand the basics of how an LDR works without delving into complicated explanations. It is first necessary to understand that an electrical ...

1. LDR-experimentation.pdf
pg. 1
COVENTRY UNIVERSITY
Faculty Of Engineering & Computing
AAEE
Light Depended Resistors (LDRs)
Introduction
The light dependent resistor, LDR, is known by many other
names such as photoresistor,
photoconductor, photoconductive cell, or simply the photocell.
These devices were discovered by an
English electrical engineer Willoughby Smith back in 1873.
Smith’s main line of work in 1848 was the
laying of underwater telegraph cables. He developed a method
of testing an underwater cable as it
was being laid. One of the insulation materials used for the
cable was selenium. Upon investigation
of the properties of the selenium insulator he discovered that
the conductivity properties of the
material were affected by light. He published his findings in
1873.
Since then many variants of photoconductive devices have been
made. Other LDRs have been made
using materials including cadmium sulphide, lead sulphide, and
the more commonly used

2. semiconductor materials including germanium, silicon and
gallium arsenide.
The most popular material used in making LDRs is cadmium
sulphide (CdS).
The LDR finds many uses as a low cost photo sensitive element
and was used for many years in
photographic light meters as well as in other applications such
as lighting controls for street lamps
etc.
Basic structure of an LDR
There are many ways in which light dependent resistors can be
manufactured. Essentially the LDR
consists of a resistive material sensitive to light. The photo
resistive element comprises section of the
material with contacts at either end. Although many of the
materials used for light dependent
resistors are semiconductors, when used as a photo resistor,
they are used only as a resistive and
they are purely passive.
A typical structure for a light dependent or photo resistor uses
an active semiconductor layer that is
deposited on an insulating substrate. The semiconductor is
normally lightly doped to enable it to have
the required level of conductivity. Contacts are then placed
either side of the exposed area.
Fig 1 (a,b,c) Close-Up of an LDR (a) Cadmium
sulphate (b) and LDR symbol (c)
(a)
(b)

3. (c)
pg. 2
In many instances the area between the contacts is in the form
of a zig zag, or interdigital pattern.
This maximises the exposed area and by keeping the distance
between the contacts small it enhances
the gain (see Fig.1 (a).
Although other devices such as photodiodes or photo-
transistors can also be used for light sensing
applications, LDRs are a particularly convenient electronic
component to use. They provide large
change in resistance for changes in light level. They are of
comparatively speaking of a lower cost as
compared to other light responding devices.
How an LDR works
It is relatively easy to understand the basics of how an LDR
works without delving into complicated
explanations. It is first necessary to understand that an
electrical current consists of the movement of
electrons within a material. Good conductors have a large
number of free electrons that can drift in a
given direction under the action of a potential difference.
Insulators with a high resistance have very
few free electrons, and therefore it is hard to make the them
move and hence a current to flow.
An LDR or is made from a semiconductor material with a high
resistance. It has a high resistance

4. because there are very few electrons that are free and able to
move - the vast majority of the
electrons are locked into the crystal lattice and unable to move.
Therefore in this state there is a high
LDR resistance.
As light falls on the semiconductor, the light photons are
absorbed by the semiconductor lattice and
some of their energy is transferred to the electrons. This gives
some of them sufficient energy to
break free from the crystal lattice so that they can then conduct
electricity. This results in a lowering
of the resistance of the semiconductor and hence the overall
LDR resistance.
The process is progressive, and as more light shines on the LDR
semiconductor, so more electrons
are released to conduct electricity and the resistance falls
further.
LDR summary
LDRs are very useful components that can be used for a variety
of light sensing applications. As the
LDR resistance varies over such a wide range, they are
particularly useful. In order to utilise these
components, it is necessary to know how an LDR works, can
how it could be used as a light sensing
element that could be used for the control of our robotic
vehicle.
Experimentation
In the experimentation that follows we will examine two
different types of LDRs and we will carry out
some measurements that will help to evaluate the operational
parameters and uses of LDRs. Some of

5. the experimentation will involve the interfacing of the device to
our PIC18 microcontroller and
associated peripherals using both Digital and Analogue I/O
interfacing methods.
pg. 3
Apparatus
LDR modules (2 different types supplied)
Torch
5 volt fixed PSU and connecting leads
Digital multimeter (for voltage and resistance measurement)
Breadboard
10k ¼ resistor
Other resistors to be selected by user calculations
Light meter (if available)
For the PIC interface part of the laboratory you will ALSO need
the following:
PC with MPLAB V5.6 or higher and USB port
ICD 3 and USB lead

6. PIC18F4520 Target board
ADC Potentiometers board and IDC10 way connecting cable
PIC18 Prototyping board and 10way ICD connector, 2-way
connecting lead for Port B
10-LED Bargraph display
3 x 270R resistors
Extra LED
Connecting wire links
Task 1 Identifying the resistance variation Versus incident
light
Connect an Ohmmeter across the terminals of one of your
supplied LDR devices. (See diagram Fig.3)
Take a range of measurements of device resistance versus
incident light. Ideally you will need a light
meter for this task. If this is not available use ambient light
readings, as well as a variety of other
readings i.e. fully covering up your device with your finger or
other means and by using your torch to
shine a light on your LDR at from various distances.
Repeat the exercise for the second type of LDR supplied.
Discuss your findings and compare the results/readings from the
two devices.
Compare your results with the data sheet of one of your devices
as supplied in the Appendix.
Fig.3 System setup for Task 1
Fig.2

7. Light meter
pg. 4
Task 2 LDR in a voltage divider arrangement
In Task 1 we investigated the resistive response of the LDRs in
a stand-alone arrangement
examining the resistive changes of the device in response to the
incident light on the device.
In Task 2 will examine the use of an LDR in a Potential Divider
circuit arrangement and investigate its
use in a real light sensing situation when a voltage change
across it, or across the associated part of
the circuit can be used to measure/control an application in
mind.
For this exercise we will connect one of the LDRs to the circuit
configuration shown below in Fig 4 (a
and b). From the previous results from Task1 choose the LDR
that you think is best suited for this.
Resistor Rx has an initial value of 10K. The value of Rx will be
changed later on after you
have identified the operation parameters of the circuits.
Fig. 4 (a and b) Circuit diagram connection for task 2
Procedure
You are going to investigate the behaviour of these two circuits.
Later on you will also need to find
out how to choose a sensible value for resistor Rx in the voltage

8. divider circuit.
Connect the circuit shown in Fig.4 (a). Note that your Vcc
supply voltage is set to +5volt.
Start with a fixed Rx value of 10k . Connect this to the bottom
part of your voltage divider circuit.
Connect a voltmeter across your Rx (10K) resistor. Take a
number of readings of your Vout under a
varying light illumination condition. Create a table and enter
measured voltage values.
The formula for calculating Vout is as follows:
Change Rx to a 5k value take similar measurements as before
and place them in another table.
Compare the two tables, comment on your findings and verify
the above equation.
Repeat the above exercise by swapping the Rx and LDR
positions as shown in Fig.4 (b).
(a) (b)
pg. 5
Considering that our Robotic Vehicle will be using LDRs for
light direction control choose the
appropriate Rx value by calculations and experimentation so
that the LDR provides the appropriate
voltage output level for a recognised logic 1 (between 2.5 and 5
volt) when illuminated at an
accepted distance from the sensor without any interference from

9. ambient light changes/fluctuations
and a logic level 0 (between 0 and 0.7 volts) when LDR is not
illuminated.
Remember that in this instance we will be using two discrete
light levels of Illumination / NO
Illumination that will relate to corresponding logic levels of 1
and 0 that could be recognised by a
digital input Port pin of the micro (use PortC).
Further experimentation
1. In the further experimentation that will follow you will need
to focus upon the interfacing
methods in connecting the potential divider’s output (LDR/Rx
arrangement) to the PIC18
micro’s configured Input Port C0 pin that will sense and
respond to incident light by an
illuminating/flashing an LED on the same Port that has been
configured as output. You will
need to decide upon the potential divider configuration and the
appropriate Rx value
calculated/chosen.
2. For the second part to this LDR/PIC18 interfacing study you
will need to refer back to your
previous ADC experimentation.
Connect the voltage divider’s Vout to the AN0 pin (channel 0)
of Port A as shown in Fig. 5.
Convert the Light dependant varying analogue input to your
ADC and display its digital
representation on output Ports D and B as we have seen in the

10. previous ADC experimentation.
Decide upon the acceptable light threshold levels and flash an
output LED on an output pin of
PortC0.
P. Abatis Doc/LDR V2.0
http://web1.eng.coventry.ac.uk/Panos/Info/Experiments/Micros/
202CDE/LDR%20experimentation.pdf
Fig. 5
Connecting the LDR to
the PIC18 ADC
http://web1.eng.coventry.ac.uk/Panos/Info/Experiments/Micros/
202CDE/LDR%20experimentation.pdf
pg. 6
APPENDIX
pg. 7

11. Light Depended Resistors (LDRs)Basic structure of an LDRHow
an LDR worksLDR summary
lab-details.docx
102SE Activity Led Learning Project
Introduction
In this project we will apply our previous experimental work of
the PIC in connection with the earlier work we undertook on the
light dependent resistor plus we will use the programming
experience and experimental activity to:
1. Develop and refine a project specification
2. Work together as members of a team to undertake a specific
task
3. Design and implement a prototype (sub system component,
system component)
4. Implement test and quality procedures
5. Design suitable container for the cell.
6. Describe a method of communication between the cell and a
central processing unit i.e. a PC.
7. Describea production process, main tasks and processes
together with a schedule of events.
8. Report project outcomes.
Scenario:
You are asked to create part of a prototype light cell that
converts optical pulses into digital electronic pulses in order to
count them. The optical switching rate is very low i.e. pulses
per minute.
Figure 1 Outline of the System
To convert optical pulses into digital pulses there is a need to

12. set up the LDR in conjunction with an electronic module (built
withOPAMPS),the functionality of the LDR setup and electronic
module is shown as per the arrangement shown in figure 2.
Figure 2 Input / Output Characteristic of LDR / Electronic
Module
Report
Each student is required to submit an individual report
(maximum 1500 words). Your report should concentrate on:
1. Design of the LDR and electronic signal conditioner part of
the light cell plus testing 35 %
2. Software Development plus testing 35 %
3. Design of container 10 %
4. Production processes an outline of main processes and
equipment 10%
5. Conclusion 10 %
Submission Date
04/04/14 Moodle 23.55
Important:Very short extracts from published sources may be
included in answers but you should avoid copying significant
amounts of text from other authors. You should note that whilst
the Internet can provide lots of information much of it is not
refereed and should be treated with caution. If you take material
from elsewhere and incorporate it in your answer word-for-
word, you must indicate where you have taken it from. A guide
to academic citation and writing is available at:
http://wwwm.coventry.ac.uk/caw/Pages/CUHarvardreferencestyl
e.asp
RFJ 2013-2014
UNDERGRADUATE RESEARCH PROJECT
Project goal:
Align student career interests with course learning outcomes
(CLOs) as defined in the Course Outline.

13. Students will choose a business manager working in an industry
that interests them and conduct the research below. This will
include two interviews as well as an experiential journal and a 5
page (1500 word) min. reflection paper.
*STUDENT MUST HAVE COMPANY NAME, MANAGER
NAME, WEBSITE, ADDRESS, PHONE NUMBER AND
EMAIL APPROVED BY PROFESSOR HAEGER BEFORE
PROCEEDING IN ORDER TO GET CREDIT FOR THE
ENTIRE PROJECT.
· Please provide the above information and date of first
interview to me in class by the due date above.
· See syllabus above for due dates of each interview transcript
(1) and 5 journal entries (all in one word doc) TO BE
SUBMITTED TO A DROPBOX IN ANGEL. These items
equate to your homework grade for the course. 5+5+5 = 15
points (15% OF YOUR GRADE).
· Final Project PAPER is due as per above syllabus (Also 15%
of your grade).
Problem Definition:
What are managers looking for in a new hire and leader? What
characteristics and competencies are they finding? Do they
match up? How does the manager lead employees?
Studies show that new entrants into the working community
lack expected leadership skills and competencies. This research
is directed toward local businesses to determine what
deficiencies and strengths exist in potential leaders being hired
today. The managers being interviewed can also provide
insights based on the way they choose to lead their employees.
Significance to society/business: New entrants will gain an
understanding of what companies are looking for in a leader.
Businesses will benefit from a richer pool of future applicants.

14. Benefits of the research:
· MCC: insight for student body relative to the work
environment and application of CLO’s to real world.
· Community: Assist students as current workers to become
more effective applicants and leaders.
· Area business: Richer pool of applicants in the future as
students apply what they have learned to their own learning
agenda.
· Researcher: Personal insight into leadership competencies and
skills relative to employer needs.
PROJECT SUMMARY:
A. Student will make contact with a hiring manager.
Student will choose an industry and make contact with a Senior
Manager or Hiring Manager.
The student will meet at least twice with the manager to gather
information. The meetings should be face to face. Student must
offer a copy of their final report to the manager. If you can get
permission it is helpful to record the interview since you will
need to type up a transcript for each.
B. Students will journal personal experiences and thoughts
throughout the project. Five entries are require in ONE word
document submitted to a dropbox in ANGEL. ONE WORD FILE
is accepted. Not five files. You will receive a zero if you
submit five documents.
Experiential Journal:Your journal is about your personal
experience during the project. What are you thinking?
The experiential journal will be five separately DATED entries.
Each entry will be from a different day and express thoughts
regarding a different phase of the project. Entries will be in

15. paragraph form, dated and at least 120 words each. Students
may journal in a free flow manner about the project. The
guidelines below are for students who have not written a journal
before and need a starting point.
· The first entry could be prior to your meetings. Please write
about the company you chose, the manager you will meet with
and a bit about the company itself. Why is this company your
choice?
· The second entry could be prior to your meetings. Please
journal about what you are expecting to find and what you think
you might learn from the experience as well as any other
thoughts you are having.
· The third entry could be after the first meeting. Please journal
about what you personally experienced during your meeting.
Perhaps add what you think will occur at the next meeting.
· The fourth entry could be after the second meeting. Please
journal about what you personally experienced during your
meeting. Add how you feel these meetings will help you with
your paper.
· The fifth entry could be a summary of the entire meeting
experience. Add how you feel this experience will help you in
your life and career.
C. Students will conduct field survey interviews/meetings.
Questions and answers will be typed up and handed in as part of
the project. (transcripts)
Field Interview Protocol:
Students will spend time in class collaborating and developing
rich surveys with which to administer and converse with the
chosen manager.

16. Survey Questions: EXAMPLES
· What knowledge, skills, and abilities is the manager looking
in a leader?
· Does age make a difference when hiring a new leader? Why?
· What are the benefits of having an education when entering
this field?
· Describe the type of person you would most likely place in a
leadership role.
· Is the person above hard to find? Why or why not? What is
missing?
· What can be taught through training?
· In a perfect world describe a new employee whom you would
assign to a leadership role.
· Additional manager comments or insights.
Students are encouraged to add questions as they surface during
the interview to enhance the study. Questions and answers are
typed up in transcript form. Transcripts submitted will be at
least 800 words. Students are encouraged to record the
meetings with permission or take notes.
D. Students will write a synthesis paper at least five pages in
length and a minimum of 1500 words.
Synthesis Paper
Students finalize this project by writing a synthesis paper
relating their field experience and journals to course concepts
and demonstrate the ability to think critically about the
experience by making connections and providing insights about

17. the field. It is suggested that students choose at least four
concepts covered in the course and synthesize them with the
responses from the interviewee. Each connection must conclude
with insights relative to similarities and differences that surface
between the field experience and the course itself. Students are
encouraged to think critically and make suggestions that are
relevant to either improving themselves, the business, or the
leadership. (Students usually see real world examples of what
we are learning in class during this project, however sometimes
they end up in a “what not to do” interview. This is excellent
fodder for a paper on improvements using applicable course
concepts.)
Please relate the significance of this project to your course
work. Select at least four course concepts that surfaced during
your interview. It is a good idea to review the first interview to
identify concepts. If you are low on ideas, the second interview
is a great time to ask more questions!
For Example: If during the interview, the manager talks about
training of employees at length, then this is a good topic for you
to discuss in your paper by connecting it to topics covered in
class and in your text. Share the main idea expressed by the
manager, then refer back to what the course (text, notes) says
about training (i.e., types of training) and then identify what
type the manager may have talked about and give an example of
how the manager carries out this training in the workplace. If
you do this, you have created the synergy intended for this
project!
Format: one inch margins, 11 pts. Double spaced. There should
not be heading except on the cover sheet. Cover sheet will have
your name, my name, the name of the course and the date.
Optional - Rough Drafts are accepted through email if you
would like my feedback up to two weeks before the due date.

18. All parts of this project with be submitted in ANGEL via a
dropbox. A document in WORD format must be attached to the
dropbox. One submission only will be allowed and one file per
dropbox assignment will be accepted.
Earthlink Company
Earthlink Company is a communications network firm based in
Atlanta Georgia. The company serves over one hundred and
fifty businesses worldwide with most of its consumers coming
from the United States. Earthlink operates under two distinct
divisions;EarthLink Consumer Services and Earthlink Business
Services. EarthLink Business Services offers connectivity
services such as the Ethernet, DS3,DSL,T-1, wireless and
MPLS. It also offers wholesale services in the field of network
services and fiber capacity. This company offers services to a
considerably huge population of the United States of America.
EarthLink has a subsidiary in Rochester, NY where they provide
technical support for online and phone services. I had the
opportunity to speak with Tom, the technical special manager
tasked with the responsibility of supervising technicians. He
also handles complains related to technical support.
What knowledge, skills, and abilities is the manager looking for
in a leader?
Tom told me that a leader should help in meeting the
organizational goals. New leaders in EarthLink Company are
expected to delegate duties to the employees in a manner that
will help meet the company’s objectives. Through their strong
career commitment, they should lead by example. With the
constant advancement of technology, leaders should keep up
with innovations by carrying out constant research. Currently,
EarthLink’s biggest challenge is increased competition from
other market players. Therefore, to ensure that their company
remains competitive, leaders must see to it that their company

19. offers the best services. The new leaders must be people who
continuously do research to ensure that the company offers the
best services. Following this, the new leader must encourage
other employees to find any useful information that might lead
to the development of unique services. The leaders must gain
the credibility of the employees and the public in general. A
leader should be in a position to instill confidence among his
employees; this ensures that the employees carry out their
duties without any hesitation. To get a job as a leader in the
EarthLink Company, a person must be very confident in making
decisions. The leader must ensure that they make well informed
decisions that will make the organization more focused on its
goals. As a manager of EarthLink Company, there are set
standards that the leaders must possess in order to qualify.
Through a series of tests, our interview panel will choose the
right person for the leadership position. Additionally, a leader
must possess the ability to make right decisions leading to an
improvement of company performance.
Describe the type of person you would most likely place in a
leadership role.
Apart from being more innovative, they must have motivational
skills. This means that a leader provides the necessary
encouragement to keep employees going. I would choose a
leader who maintains good employee welfare. This is achieved
by providing a good working environment, sufficient
remuneration, strict adherence to work ethics as well as creating
a healthy working environment. Since EarthLink Company
largely engages with young innovative people, the leader must
be very approachable. Another skill that the EarthLink company
leaders should portray is the ability to delegate responsibilities
in their departments. Delegating the duties and responsibilities
in the organization plays a key role in team building. The
employees work as a team and assist each other in income
generating activities. TheEarthLink company has several

20. departments whose success is based on the successful
completion of responsibilities from other departments. For
instance, if the production sector manufactures beverages on
time marketers will be able to carry out their duty as well as the
supplies and logistics. The new leader in Earthlink Company
must have the ability to communicate their responsibilities to
the employees using the right terms. If a leader comes up with
an idea but fails to communicate well to the employees then it
will not be well implemented. The manager needs to pass the
ideas to the employees exactly as it should be implemented so
as to gain the expected results. Earthlink employees should
understand what the leader expects them to do. The leaders
should also learn to accept criticism by listening to the opinions
that their employees have. Leaders also make mistakes and
should be able to accept what their employees do so.
What are the benefits of having an education when entering this
field?
The candidate should have a Bachelor of Science degree. The
education background of a leader is very important since it horn
his/her decision making skills. For example, Earthlink prefers
candidates who have the right educational background which
imparts them with problem solving skills. Anyone intending to
be a leader in this field should be aware of the market
population, company branches, and the firm’s level of
participation in the industry. In addition, they must have a good
grasp of the company’s growth trends and be in a position to
predict its future prospects.
Teacher Comment
This is very interesting! Remember to ask for examples so you
can use them in your paper. I look forward to reading more
about Earthlink!