For several reasons, invisible electromagnetic signals in the RF and infrared frequency spectra
are preferred for the remote control of consumer electronics. However, a niche exists for the
use of visible light for the remote control of domestic electrical fittings which require simple
power control operations. Electrical fitting controllers like light switches, light dimmers, power
sockets and ceiling fan regulators can be remotely controlled by an ordinary flashlight focusing
its light beam on the detector for the fitting. The remote control signal detector compares the
luminous intensity on a light beam detector with that on an ambient luminous intensity detector
and, given a sufficient difference, initiates a cyclic controller output sequence. The output
cycles, changing the state of the controlled fitting from OFF to ON (at different ON states if
applicable) and back OFF. The design of a simple and sufficiently sensitive light beam detector
that can function properly and reliably in all indoors ambient lighting conditions was the main
focus of this thesis. The luminous intensity difference detector designed uses two light
dependent resistors (LDRs) in special enclosures which increased their sensitivity to a focused
light beam in high levels of ambient illumination. A UA741C Op-Amp IC based comparator is
used to detect a difference in illuminance between the ambient illumination and the extra
illuminance as a result of a focused light beam on the light beam detector. The light remote
controlled ceiling fan regulator realized using the luminous intensity difference detector has a
control range which competes favorably with infra-red remote controlled systems. The
luminous intensity difference detector can be used in security systems, motion sensing,
robotics, sunlight tracking systems and many emerging applications of optoelectronics.
TABLE OF CONTENTS
TITLE PAGE ————————————————————————————–i
TABLE OF CONTENTS ——————————————————————–vii
LIST OF TABLES —————————————————————————–x
LIST OF FIGURES —————————————————————————–xii
LIST OF APPENDICES ——————————————————————–xiv
1.1 Introduction ———————————————————————1
1.2 Thesis Motivation ————————————————————2
1.3 Literature Review ————————————————————3
1.4 Problem Definition ————————————————————6
1.5 Methodology ———————————————————————7
1.6 Thesis Outline ———————————————————————8
LUMINOUS INTENSITY DIFFERENCE DETECTOR DESIGN —————-9
2.1 Introduction ———————————————————————-9
2.2 The Light Sensor ————————————————————15
2.3 The Operational Amplifier —————————————————16
2.4 The Op-Amp Comparator —————————————————17
2.5 The Design of the Luminous Intensity Difference Detector —————18
2.6 Input Bias Current Requirements ——————————————21
2.7 Input Bias Resistors Value Determination ———————————22
2.8 Light Dependent Resistor Sensitivity Improvement ————————26
2.9 Luminous Intensity Difference Detector Output
2.10 The Oscillator Switch ————————————————————46
2.11 The Power Supply Unit —————————————————48
TIMER AND COUNTER BASED SWITCHING CIRCUIT ————————51
3.1 Introduction ———————————————————————51
3.2 The 555 Timer IC Based Clock Pulse Generator ————————52
3.3 The CD4017BC IC Based Output Switch Control Circuit —————57
3.4 The Relay Based Ceiling Fan Regulator Output Switches —————59
THE COMPLETE LIGHT ACTIVATED REMOTE
CONTROLLED FAN REGULATOR SYSTEM ——————————————64
4.1 Introduction ———————————————————————64
POWER REQUIREMENTS, CONSTRUCTION, TESTING AND
5.1 Introduction ———————————————————————72
5.2 Power Requirements ————————————————————72
5.3 Construction ———————————————————————83
5.4 Testing ———————————————————————85
5.5 Installation ———————————————————————86
CONCLUSIONS, LIMITATIONS AND RECOMMENDATIONS —————87
6.1 Introduction ———————————————————————87
6.2 Conclusions ———————————————————————88
6.3 Limitations ————————————————————91
6.4 Recommendations ————————————————————92
The remote control of household and industrial electronics and electrical devices and
systems by means of wireless handheld controllers is not uncommon today. These
controllers make use of electromagnetic waves of different spectra. Usually the frequency
of the electromagnetic waves used for control is selected from the ranges of frequencies
that are not generated internally by the controlled device or externally in the ambient
surroundings of the target environment where the controlled device is to be used.
The control signals are restricted to narrow bandwidths and are expected to be of very
specific format at the receiver of the controlled device. These measures are taken to
ensure that the controlled device does not respond to random electromagnetic
phenomena, to ensure reliability in operation of the controlled system and for control
The most popular and widely used spectrum for remote control systems today is the infrared
range of frequencies. Most consumer electronics and electrical devices in use today
are of the infrared type. Infrared signals are invisible to the naked eyes and so the signals
are not focused into a narrow beam when used in remote control systems. Therefore
accurate pointing of the remote controller to the detector of the controlled device is not
necessary, making them easier and more convenient to use.
Examples of consumer electronics that commonly have remote control facility are
television sets, video cassette recorders, and compact disc players. Electrical products
with remote control facility are less common and include mostly climate control
equipment like fans and air conditioners. Each of these electrical systems is purchased
with its own very specific remote controller. It is not uncommon to have up to five
different remote controllers in a residential sitting room alone.
Electromagnetic waves of the visible light spectrum is generally not used for remote
control systems for several obvious reasons which include the high likelihood of
interference from natural and man made light sources which exist in almost all
environments where electrical equipment are deployed, the higher power for visible light
generation and preference for unobtrusive, discrete and invisible control signals.
However, a small niche exists for the use of visible light for the remote control of
electrical and electronics systems, this includes simple power “on” and “off” operations,
speed or intensity control of multiple home electrical fittings using a single controller.
Picture a scenario whereby one can put the bedroom lights on and off, turn the ceiling fan
on to any of the preset speeds and also turn the air conditioning unit on and off from ones
bed, using the same remote control device – a flashlight, just by focusing the beam of
light on the detector of the device to be controlled.
1.2 THESIS MOTIVATION
This work aims at developing a means of incorporating a remote control alternative into
electrical fitting controllers, namely light switches, power outlets (sockets), dimmer
switches and ceiling fan speed regulators. Lower levels of illumination in the interior
usually characterize homes, unlike office buildings, even when artificial light sources are
used. This is logical as our homes serve as a shelter from the extremes of the outdoor
physical conditions. The desire is to develop a reliable, yet simple means of controlling
all the lights, ceiling fans and some other selected electrical fittings connected to wall
sockets, for example air-conditioners. Remote control is not desirable for devices like
electric stoves, deep freezers and refrigerators, which are best manually controlled.
A single controller is desired for the control of all the electrical fittings. This will prevent
the unnecessary clutter of specialized controllers for similar devices.
1.3 LITERATURE REVIEW
The use of remote control for electrical fittings lacks a concise history. Often,
manufacturers and consumers deem the inclusion of extra intelligence and the associated
cost of remote control for simple routines like powering On/Off of light switches, airconditioners
and ceiling fan regulators as economically unjustifiable. At present, infra-red
remote control of lights, power switches and ceiling fans are available. They are available
mostly only on special request and require a separate controller (transmitter) for each
Layton  revealed that the world’s first remote controls were radio-frequency (RF)
devices that directed German naval vessels to crash into Allied boats during World War I.
In World War II, remote controls detonated bombs for the first time. The dominant
remote-control technology in home-theater applications is infrared (IR). Infrared light is
also known as plain-old “heat.” The basic premise at work in an IR remote control is the
use of light to carry signals between a remote control and the device it’s directing.
Infrared light is in the invisible portion of the electromagnetic spectrum. An IR remote
control (the transmitter) sends out pulses of infrared light that represent specific binary
codes. These binary codes correspond to commands, such as power on/off and volume
up. The IR receiver in the TV, stereo or other device decodes the pulses of light into the
binary data (ones and zeroes) that the device’s microprocessor can understand. The
microprocessor then carries out the corresponding command.
Brain  gave a detailed description of a typical TV infrared remote controller with
emphasis on its internal physical structure and its operation.
The focus of this work, the use of visible light as a pointing device for the remote control
of power to multiple electrical fittings in the home is not rich in precedence.
Visible light is commonly used to activate or deactivate electrical/electronic processes
through the use of Photodiodes, Photocells/Light Dependent Resistors (LDRs) and
Phototransistors as light sensors. The LDR is the most popular for ambient illumination
In an optoelectronics experiment by Phillips , it was stated that an LDR must be part
of a voltage divider network in order to give an output voltage, which changes with
illumination. It was shown that there are just two ways of constructing the voltage divider
network, with the LDR at the top, or with the LDR at the bottom of the voltage divider. It
concluded that the optimum value of fixed resistor, that gives the biggest changes in the
output voltage, is when the fixed resistor value is equal to the resistance of the LDR.
Collinson  used a single LDR, the popular ORP12, in a potential divider network to
activate an external light or buzzer whenever the LDR is exposed to dark ambient
lighting conditions. The UA741 Operational Amplifier IC, powered by a single polarity
DC supply, was used for the voltage comparison and subsequent activation.
Similarly Van Roon  used a single LDR in a voltage divider network to bias an NPN
transistor, which controls the On/Off state of a relay. The circuit is light activated when
the LDR is placed at the top of the potential divider network and is dark activated when
the LDR is placed at the bottom.
It is important to note that all light and/or dark activated or light controlled systems use a
single LDR in a potential divider network and are either threshold systems, where the
activation/deactivation of a process is based on a particular level of illumination, or
proportional systems, where the magnitude of the output variable is directly or inversely
proportional to the level of illumination.
This thesis undertakes the design of a simple luminous intensity difference detector
circuit than can be used to detect a beam of light for visible light remote control system.
The circuit will use two light dependent resistors in a voltage divider network to detect a
visible light remote control signal. The design objective is to use the LDRs in a
comparative configuration. That is, a circuit which will use the LDRs in a non-threshold
or proportional manner. The activation/deactivation of the output of the detector will
depend on the difference between the levels of illumination on two different surfaces.
This thesis also undertakes the design of a special enclosure for the LDR to improve its
sensitivity to a focused light beam in the presence of high levels of ambient illumination.
The comparative circuit configuration and the special LDR enclosure are intended to
make the remote control signal detector to be very sensitive and reliable in a wide range
of ambient illumination This work, therefore, presents a third way of using LDRs in a
potential divider network.
1.4 PROBLEM DEFINITION
To realize a simple remote control system for electrical fittings which uses visible light as
the control signal, many questions need to be asked like; Why visible light?, How reliable
would the system be?, Will the system work in the presence of bright light as well as in
the dark?, etcetera.
A room in a typical home could have at least two electrical fitting controllers for lights
and a ceiling fan, and for wiring conveniences these controllers are usually placed close
together. Fittings like air-conditioners are usually provided with dedicated power outlets
(sockets). Since this equipment require only simple power control instruction, and given
the desire for a single controller, it would be necessary for the controller to be able to
select the device it is controlling at any point in time. Otherwise an “on” instruction from
the controller will turn on all the remotely controlled equipment simultaneously.
A focused beam of light in a pointing device, like a flashlight, can be pointed to the
detector of the particular fitting to be controlled. Since the beam of light can be seen, it
can be brought to focus on any selected surface, individual devices can be separately
controlled by focusing the beam on its detector only. Battery powered flashlights
(torchlight) are ubiquitous, cheap and can be easily obtained. Most households have a
couple of them.
In order to use a focused beam of light for remote control, the light sensor of the
controller must be sensitive to the beam of light from a reasonable distance even in the
presence of high level of ambient illumination as is obtainable indoors in residential
buildings. The system must be designed to be reliable, free from false triggering by
random light sources and power line voltage fluctuations. These are the challenges that
must be overcome in the realization of a practicable luminous intensity difference remote
The design of the luminous intensity difference remote controlled electronic ceiling fan
regulator will be carried out by:-
a) Designing an electronic circuit that can detect a difference between the ambient
illumination and the illumination as a result of a focused beam of light from the
controller and use this detection to initiate a simple control process. The light
beam detector circuit is expected to be sensitive to the beam of light from a
distance of about 4.0m in daytime illumination and even farther in the dark of
b) Selecting a light sensitive electronic component, studying its electrical
characteristic and finding a means of improving its sensitivity, in the presence of
high levels of ambient illumination, if necessary.
The emphasis of the design of the luminous intensity difference detector is;
i) Simplicity and Economy, it should use as few components as possible to make a
simple and direct comparison between the light intensities reaching two different
light sensitive devices,
ii) Selectivity, in terms of its ability to respond only to the control signal and not
random or transient light sources
iii) Reliability, in terms of its ability to respond to the control signal correctly and
without failure and,
iv) Noise Immunity, in terms of its freedom from the negative effects of power
fluctuations and random physical phenomena in the semi-conductor material that
make up the light sensitive components.
Finally, an equally reliable electronic circuit that will control the electrical appliance, in
this case a ceiling fan regulator will be designed.
1.6 THESIS OUTLINE
This thesis consists of six chapters. Chapter One is an introduction to the topic of wireless
remote control of electronic/electrical systems. Chapter Two is a description of the
observations, investigations and experimentation that were carried out on the Light
Dependent Resistor (LDR). Chapter Three describes the design of the timer and counter
based electronic ceiling fan regulator circuit. In Chapter Four, three parts of the system
are coupled together. The circuit diagram of the assembly of these parts of the system is
presented and the explanation of its operation is provided. Chapter Five provides the
power consumption estimation for the Light Activated Remote Controlled Fan Regulator;
it discusses the systems construction and testing. Chapter Six is a conclusion of the work
done in the thesis, it presents results obtained and proffers general recommendations and
suggestions for further work.
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