AUTOMATIC ROOM LIGHT CONTROLLER
Usually when we enter in our room in darkness, we find it difficult to
locate the wall mounted switchboard to switch on the light, for a stranger, it
is tougher still as he has no knowledge of the correct switch to be turned on.
Here is a reliable circuit that takes over the task of switching on and
switching off of the lights automatically, when somebody enters or leaves
the room during darkness. This circuit has the following features.
The lights turns off only when the room is vaccent, or in other words, when
all the persons who entered the room have left.
A seven segment display shows the number of persons currently inside the
room.
In this project we use two infra red sensors. Both connected in the door. Two
photodiode’s are also connected to the receiver circuit to detect the infra red
signal. Both the infra red sensor is connected to the ic 555 as a monostable
timer. In attach with the sensor and 555 we use one up down counter circuit.
Up down counter increment and decrement the input pulses and display it
on the seven segment display. One logic circuit to compare the total number
of person in the room is also involved in this project. For this purpose we
use ic 7485 4 bit binary comparator to compare the total number of person
in the room.
One relay driver circuit to interface the main lights or fan with this unit.
Relay provide a high voltage to the fan and lights for proper working.
In this monostable timer we use ic 555 . Pin no 8 of this ic is connected to
the positive supply. Pin no 1 is connected to the negative supply. Pin no 2 Is
connected to the photodiode. In this project we use two
555 ic. Working of this project is just like this when When any body enter in
the room then one infra red sensor is active and one ic is enable and at this
time second 555 is disable. When any person came out from the room then
other 555 is on and disable first ic and enable this second one. Note that only
one sensor is on at a time. With the help of this ic we give a up and down
pulse to the up – down counter.
Photodiode is connected to the pin no2 via 22 k ohm reistor. 22 k ohm is
grounded from the . In normal way when we switch on the circuit both the
infra red sensor is on and light is fall on the photodiode. Now when any
body enter in the room then circuit sense the intruption and at this time 555
gives its output. Output from the this 555 is connected to the up-down
counter through npn transistor. Here we get this output from the collector
of the transistor. This collector point is also connected to the pin no 4 of
second ic. Output available on the collector point is negative and due to this
pin no 4 of the next ic is become negative and hence this 555 is off. With the
help of this logic at a time we switch on one ic and off the second one by
controlling a pin no 4 by giving a negative voltage on pin no4.
Our next circuit is ic 74192. Ic 74192 is a up down counter. Pin no 16 and
11 is connected to the positive supply. Pin no 1,8,9 is connected to the
ground voltage… Pin no 4 and 5 is clock input for up and down pulses. This
up and down pulse is from the two ic 555. Pin no 14 of this circuit is
connected to the master reset pin 14. . Pin no 2,6,7,3 is output pin of this ic.
These output are in bcd output and in flip flop mode. Pin no 15 and 10 of
this ic is connected to the ground pin.
Output of this up/down counter is further connected to the 4 bit binay
comparator circuit. BCD output from the up down counter is connected to
the ic 7485 and ic 7447. IC 77485 compare the magnitutde of this output
and compare this output to the ground pin 9.11.14.1. when there is any
single output on the 7485 then pin no 5 of this comparator is high and and
switch on the relay coil.relay further switch on the output bulb to on. When
BCD is connected to the 7485 and at the same time this bcd is connected to
the ic 7447 to display the seven segment code.
Now when any body enter in the room then ic 555 sense the signal through
photodiode and then this signal is further connected to the ic 74192 for
clock up signal . this ic gives its output in BCD form and then this output is
now connected to the two ic no 1 ic 7485 and ic 7447. Output of the ic
7447 is connected to the common anode segment display. IC 7485 compare
the bcd signal to the ground potential when all the bcd is zero then there is
no output on the pin no 5. If single bcd is high then pin no 5 become high
and output bulb is on.
CIRCUIT DIAGRAM.
SENSOR LOGIC.
In this project we show that how we save the valuable
energy. Not only save the valuable energy but for security
reason we use this project in many audiotoriam . Where we
want to check the total person to be entered or exit.
First part of this project is Infra red sensor. Here we use infra
red sensor as a transmitter and photodiode as a receiver.
When any body cross the infra red beam then circuit provide
a sharp pulse and circuit recognize the pulse for counting.
In this project we use two beams of lights. Every person
cross this two beams. By crossing these beams in steps we
check the interruption of entery in the room or exit from the
room.
Photodiode in this sensor is connected to the ic 555. here ic
555 work as a monostablke timer. Here we use two 555
timer.
Working of infra red transmitter and
receiver circuit.
Photo Transistor
A phototransistor is in essence nothing more than a normal bipolar
transistor that is encased in a transparent case so that light can reach
the Base-Collector diode. The phototransistor works like a photodiode,
but with a much higher sensitivity for light, because the electrons that
tunnel through the Base-Collector diode are amplified by the transistor
function.
Phototransistors are specially designed transistors with the base region
exposed. These transistors are light sensitive, especially when infrared
source of light is used. They have only two leads (collector and
emitter). When there is no light the phototransistor is closed and does
not allow a collector-emitter current to go through. The phototransistor
opens only with the presence of sufficient light
An opto electronic device that conducts current when exposed to light
is the PHOTOTRANSISTOR. A phototransistor, however, is much more
sensitive to light and produces more output current for a given light
intensity that does a photodiode. Figure 3-32 shows one type of
phototransistor, which is made by placing a photodiode in the base
circuit of an NPN transistor. Light falling on the photodiode changes the
base current of the transistor, causing the collector current to be
amplified. Phototransistors may also be of the PNP type, with the
photodiode placed in the base-collector circuit.
Figure 3-33 illustrates the schematic symbols for the various types of
phototransistors. Phototransistors may be of the two-terminal type, in
which the light intensity on the photodiode alone determines the
amount of conduction. They may also be of the three-terminal type,
which have an added base lead that allows an electrical bias to be
applied to the base. The bias allows an optimum transistor conduction
level, and thus compensates for ambient (normal room) light intensity.
Figure 3-33. - 2-terminal and 3-terminal phototransistors.
Applications
Infrared
Infrared (IR) radiation is electromagnetic radiation of a wavelength
longer than visible light, but shorter than microwave radiation. The
name means "below red" (from the Latin infra, "below"), red being the
color of visible light of longest wavelength. Infrared radiation has
wavelengths between 700 nm and 1 mm.
IR is often subdivided into near-IR (NIR, 0.7-5 µm in wavelength), mid-
IR (MIR (also intermediate-IR (IIR)), 5 - 30 µm) and far-IR (FIR, 30 -
1000 µm). However, these terms are not precise, and are used
differently in the various study. Infrared radiation is often linked to
heat, since objects at room temperature or above will emit radiation
mostly concentrated in the mid-infrared band
Uses
Infrared is used in night-vision equipment, when there is insufficient
visible light to see an object. The radiation is detected and turned into
an image on a screen, hotter objects showing up brighter, enabling the
police and military to chase targets.
Smoke is more transparent to infrared than to visible light, so fire
fighters apply infrared imaging equipment when working in smoke-
filled areas.
A more common use of IR is in television remote controls. In this case it is used in
preference to radio waves because it does not interfere with the television signal. IR data
transmission is also employed in short-range communication among computer
peripherals and personal digital assistants. These devices usually conform to standards
published by IrDA, the Infrared Data Association. Remote controls and IrDA devices use
infrared light-emitting diodes (LEDs) to emit infrared radiation which is focused by a
plastic lens into a narrow beam. The beam is modulated, i.e. switched on and off, to
encode the data. The receiver uses a silicon photodiode to convert the infrared radiation
to an electric current. It responds only to the rapidly pulsing signal created by the
transmitter, and filters out slowly changing infrared radiation from sunlight, people and
other warm objects.
The light used in fiber optic communication is typically infrared.
Diode
A diode functions as the electronic version of a one-way valve. By
restricting the direction of movement of charge carriers, it allows an
electric current to flow in one direction, but blocks it in the opposite
direction.
A diode's current-voltage, or I-V, characteristic can be approximated by
two regions of operation. Below a certain difference in potential
between the two leads, the diode can be thought of as an open (non-
conductive) circuit. As the potential difference is increased, at some
stage the diode will become conductive and allow current to flow, at
which point it can be thought of as a connection with zero (or at least
very low) resistance
Light-emitting diode
A light-emitting diode (LED) is a semiconductor device that emits
incoherent monochromatic light when electrically biased in the forward
direction. This effect is a form of electroluminescence. The color
depends on the semiconducting material used, and can be near-
ultraviolet, visible or infrared. Nick Holonyak Jr. (1928 - ) developed the
first practical visible-spectrum LED in 1962.
Light-emitting diodes
(various)
LED Technology
A LED is a special type of semiconductor diode. Like a normal diode, it
consists of a chip of semiconducting material impregnated, or doped,
with impurities to create a structure called a pn junction. Charge-
carriers (electrons and holes) are created by an electric current
passing through the junction, and release energy in the form of
photons as they recombine. The wavelength of the light, and therefore
its colour, depends on the bandgap energy of the materials forming
the pn junction. A normal diode, typically made of silicon or
germanium, emits invisible far-infrared light, but the materials used for
a LED have bandgap energies corresponding to near-infrared, visible or
near-ultraviolet light.
Unlike incandescent bulbs, which can operate with either AC or DC,
LEDs require a DC supply of the correct polarity. When the voltage
across the pn junction is in the correct direction, a significant current
flows and the device is said to be forward biased. The voltage across
the LED in this case is fixed for a given LED and is proportional to the
energy of the emitted photons. If the voltage is of the wrong polarity,
the device is said to be reverse biased, very little current flows, and no
light is emitted.
Conventional LEDs are made of inorganic minerals such as:
aluminium gallium arsenide (AlGaAs) - red and infrared
gallium arsenide/phosphide (GaAsP) - red, orange and yellow
gallium nitride (GaN) - green
gallium phosphide (GaP) - green
zinc selenide (ZnSe) - blue
indium gallium nitride (InGaN) - blue
silicon carbide (SiC) - blue
diamond (C) - ultraviolet
silicon (Si) - under development
LED development began with infrared and red devices, and
technological advances have made possible the production of devices
with ever shorter wavelengths.
The semiconducting chip is encased in a solid plastic lens, which is
much tougher than the glass envelope of a traditional light bulb or
tube. The plastic may be coloured, but this is only for cosmetic reasons
and does not affect the colour of the light emitted.
.
Typical Applications for
Phototransistors and IREDs
Why Use Phototransistors?
Phototransistors are solid-state light detectors that possess internal
gain. This makes them much more sensitive than photodiodes of
comparably sized area. These devices can be used to provide either an
analog or digital output signal. This family of detectors offers the
following general characteristics and features:
Low cost visible and near-IR photodetection
Available with gains from 100 to over 100,000
Moderately fast response times
Available in a wide range of packages including epoxy coated,
transfer molded, cast, hermetic packages and in chip form
Usable with almost any visible or near infrared light source such
as LEDs, neon, fluorescent, incandescent bulbs, laser, flame
sources, sunlight, etc....
Same general electrical characteristics as familiar signal
transistors (except that incident light replaces base drive
current)
Can be specially selected to meet the requirements of your
particular application
Why Use IREDs?
IRED's are solid state light sources which emit light in the near-IR part
of the spectrum. Because they emit at wavelengths which provide a
close match to the peak spectral response of silicon photodetectors
both GaAs and GaAlAs LEDs are often used with phototransistors and
photodarlingtons. Key characteristics and features of these light
sources include:
Long operating lifetimes
Low power consumption, compatible with solid state electronics
Narrow band of emitted wavelengths
Minimal generation of heat
Available in a wide range of packages including epoxy coated,
transfer molded, cast and hermetic packages
Low cost
Can be specially selected to meet the requirements of your
particular application
Applications
Phototransistors can be used as ambient light detectors. When used with a controllable
light source, typically and LED, they are often employed as the detector element for
optoisolators and transmissive or reflective optical switches. Typical configurations
include:
Optoisolator
The optoisolator is similar to a
transformer in that the output is
electrically isolated from the input.
Optical Switch
An object is detected when it
enters the gap of the optical switch
and blocks the light path between
the emitter and detector.
Retro Sensor
The retrosensor detects the
presence of an object by
generating light and then looking
for its reflectance off of the object
to be sensed.
Phototransistors and IREDs have been used in the following
applications.
Computer/Business Equipment
track zero detector - floppy
drive
margin controls - printers
read finger position - touch
Consumer
coin counters
position sensors - joysticks
remote controllers - toys,
screen
detect holes - computer card
monitor paper position -
copiers
Industrial
LED light source - light pens
security systems
safety shields
encoders - measure speed
and direction
photoelectric controls
appliances, audio/visual equipment
games - laser tag
Medical
provide electrical isolation between
patient and equipment
monitor intravenous injection rates
Basic of the ic 555 as a monostable timer.
The 555 timer IC was first introduced around 1971 by the Signetics
Corporation as the SE555/NE555 and was called "The IC Time Machine"
and was also the very first and only commercial timer ic available. It
provided circuit designers and hobby tinkerers with a relatively cheap,
stable, and user-friendly integrated circuit for both monostable and astable
applications. Since this device was first made commercially available, a
myrad of novel and unique circuits have been developed and presented in
several trade, professional, and hobby publications. The past ten years some
manufacturers stopped making these timers because of competition or other
reasons. Yet other companies, like NTE (a subdivision of Philips) picked up
where some left off.