16-01-2013, 03:20 PM
INTELLIGENT AUTOMATIC STREET LIGHT CONTROL SYSTEM USING HIGH SENSITIVITY LDR
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ABSTRACT
Automatic Street Light Control System is a simple yet powerful concept,
which uses transistor as a switch. By using this system, manual work is eliminated
upto the maximum extent. It automatically switches ON the street lights when the
sunlight goes below the visible region of our eyes. This is done by a sensor called
Light Dependent Resistor (LDR) which senses the light actually like our eyes. It
automatically switches OFF lights whenever the intensity of sunlight is highly
sufficient for the person to see.
By using this system, energy consumption is also reduced because nowadays
the manually operated street lights are switched off late in the morning and are
switched on early before sunset. This project clearly demonstrates the working of
transistor in saturation region and cutoff region and also the working of all the
components is clearly explained in this project.
POWER SUPPLY:
The input to the circuit is applied from the regulated power supply. The a.c. input i.e.,
230V from the mains supply is step down by the transformer to 12V and is fed to a
rectifier. The output obtained from the rectifier is a pulsating d.c voltage. So in order
to get a pure d.c voltage, the output voltage from the rectifier is fed to a filter to
remove any a.c components present even after rectification. Now, this voltage is given
to a voltage regulator to obtain a pure constant dc voltage.
Transformer:
Usually, DC voltages are required to operate various electronic equipment and
these voltages are 5V, 9V or 12V. But these voltages cannot be obtained directly.
Thus the a.c input available at the mains supply i.e., 230V is to be brought down to the required voltage level. This is done by a transformer. Thus, a step down
transformer is employed to decrease the voltage to a required level.
Rectifier:
The output from the transformer is fed to the rectifier. It converts A.C. into
pulsating D.C. The rectifier may be a half wave or a full wave rectifier. In this project,
a bridge rectifier is used because of its merits like good stability and full wave
rectification.
Filter:
Capacitive filter is used in this project. It removes the ripples from the output
of rectifier and smoothens the D.C. Output received from this filter is constant until
the mains voltage and load is maintained constant. However, if either of the two is
varied, D.C. voltage received at this point changes. Therefore a regulator is applied at
the output stage.
Voltage regulator:
As the name itself implies, it regulates the input applied to it. A voltage
regulator is an electrical regulator designed to automatically maintain a constant
voltage level. In this project, power supply of 5V and 12V are required. In order to
obtain these voltage levels, 7805 and 7812 voltage regulators are to be used. The first
number 78 represents positive supply and the numbers 05, 12 represent the required
output voltage levels.
KIND OF RESISTORS
CARBON FILM
The carbon film type is the most popular resistor type. This resistor is made by
depositing a carbon film onto a small ceramic cylinder. A small spiral groove cut into
the film controls the amount of carbon between the leads, hence setting the resistance.
Such resistors show excellent reliability, excellent solderability, noise stability, moisture stability, and heat stability. Typical power ratings range from 1/4 to 2 W.
Resistances range from about 10 Ohm to 1 Mega ohm, with tolerances around 5
percent.
FOIL RESISTORS
Foil resistors are similar in characteristics to metal film resistors. Their main
advantages are better stability and lower temperature coefficient of resistance (TCR).
They have excellent frequency response, low TCR, good stability, and are very
accurate. They are manufactured by rolling the same wire materials as used in
precision wire wound resistors to make thin strips of foil. This foil is then bonded to a
ceramic substrate and etched to produce the value required. They can be trimmed
further by abrasive processes, chemical machining, or heat treating to achieve the
desired tolerance. Their main disadvantage is that the maximum value is less than
metal film resistors. The accuracy is about the same as metal film resistors, the TCR
and stability approaches precision wire wounds but are somewhat less because the
rolling and packaging processes produce stresses in the foil. The resistive materials
used in precision wire wound resistors are very sensitive to stresses, which result in
instability and higher TCS. Any stresses on these materials will result in a change in
the resistance value and TCR, the greater the stresses, the larger the change. This type
can be used as strain gauges, strain being measured as a change in the resistance.
When used as a strain gauge, the foil is bonded to a flexible substrate that can be
mounted on a part where the stress is to be measured.
POWER FILM
Power film resistors are similar in manufacture to metal film or carbon film resistors.
They are manufactured and rated as power resistors, with the power rating being the
most important characteristic. Power film resistors are available in higher maximum
values than the power wire wound resistors and have a very good frequency response.
They are generally used in applications requiring good frequency response and/or
higher maximum values. Generally, for power applications the tolerance is wider. The
temperature rating is changed so that under full load, the resistor will not exceed the
maximum design temperature. The physical sizes are larger and, in some cases, the
core may be made from a more head conductive material and other means employed
to help radiate heat.
PHOTORESISTORS AND THERMISTORS
These are special types of resistors that change resistance when heat or light is
applied. Photoresistors are made from semiconductive materials, such as cadmium
sulfide. Increasing the light level will decrease the resistance. This type also called
LDR (Light Dependent Resistor). Thermistors are temperature sensitive resistors.
Increasing the temperature will decrease the resistance (in most cases). This type also
called Thermistor NTC (Negative Temperature Coefficient). The reciprocal type is
Thermistor PTC (Positive Temperature Coefficient). Increasing the temperature will
increase its resistance.