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P a g e | 1
1.INTRODUCTION
1.1 OUR OBJECTIVE AND APPROACH
Objective - To design an Automatic room light controller system that automatically
switches on lights in a room when a person enters the room and switch them off when
the room is empty.
Approach - Using infrared sensors to sense the entry or departure of a person from the
room and microcontroller circuit that counts the number of persons inside the room,
which is displayed on a 7-segment LED. The microcontroller operates the relay to switch
on-off the lights.
1.2 What is Automatic Room Light Controller
This Project “Automatic Room Light Controller with Visitor Counter using
Microcontroller” is a reliable circuit that takes over the task of controlling the room
lights as well us counting number of persons/ visitors in the room very accurately. When
somebody enters into the room then the counter is incremented by one and the light in
the room will be switched ON and when any one leaves the room then the counter is
decremented by one. The light will be only switched OFF until all the persons in the
room go out. The total number of persons inside the room is also displayed on the seven
segment displays. The microcontroller does the above job. It receives the signals from
the sensors, and this signal is operated under the control of software which is stored in
ROM. Microcontroller AT89S52 continuously monitor the Infrared Receivers, When any
object pass through the IR Receiver's then the IR Rays falling on the receivers are
obstructed this obstruction is sensed by the Microcontroller.
P a g e | 2
1.3 How Visitors are counted by Counter?
When the 1st person enter in to the room the LED sense that and the counter increased
by one, the phenomena repeats according to that how many persons enter to the room.
And when one person leave the room the counter decrease by one. But here is a
problem that how the LEDs sense that the person enter or leave the room? To
overcome this problem we have to detect the direction of motion of the person. For
that we two pairs of LEDs, the 1st pair is attached at the front portion of the door and
the 2nd pair is attached at the rear portion of the door. So if the 1st pair if LEDs sense a
person and then the 2nd pair of LEDs sense that person then it increase the counter by
one and the criteria denoted by entering of an person. And vice versa is denoted by
leaving of a person and that time the counter is decreased by one.
1.4 How seven segment display works?
A seven-segment display is a group of light emitting diodes (LEDs) arrange in a figure 8
pattern. The understand how the display works lets investigate how an LED works.
When charge carriers flow through a diode, the electrons flow one direction, The higher
energy electrons travel in the higher energy conduction band of the diode.
The holes travel in the lower energy valance band. The negative charge of the electrons
is attracted to the positive charge of the hole. When the electron “falls” into the hole,
recombination has occurs, energy released is in the form of a photon. The higher the
energy given up, the high the frequency of the wave. We observe this energy in our eyes
as the color of light. Our eyes are only sensitive to a limited range of frequency. Lower
energy waves are perceived as red.
By using this LEDs arranged in a figure ‘8’ pattern the seven segment display made.
P a g e | 3
Its operating principle is to input a four-bit BCD (Binary-Coded Decimal) value, and
energize the proper output lines to form the corresponding decimal digit on the 7-
segment LED display. The BCD inputs are designated A, B, C, and D in order from least-
significant to most-significant. Outputs are labeled a, b, c, d, e, f, and g, each letter
corresponding to a standardized segment designation for 7-segment displays. Of course,
since each LED segment requires its own dropping resistor, we must use seven 470 Ω
resistors placed in series between the 4511's output terminals and the corresponding
terminals of the display unit. Most 7-segment displays also provide for a decimal point
(sometimes two!), a separate LED and terminal designated for its operation. All LEDs
inside the display unit are made common to each other on one side, either cathode or
anode.
1.5 How Microcontroller Works?
Our project is basically a microcontroller based project. The main fundamental concept
is implemented in this project by microcontroller. Microcontroller AT89S52 is used here
for continuous monitoring the current status of the system. According to the status it
produce the output in the seven segment display and also the mechanism of the lights,
fans are also controlled by this controller.
P a g e | 4
2. OUR IMPLEMENATION
2.1 DESIGN DESCRIPTION
This Project “Automatic Room Light Controller with Visitor Counter using
Microcontroller” is a reliable circuit that takes over the task of controlling the room
lights as well us counting number of persons/ visitors in the room very accurately. When
somebody enters into the room then the counter is incremented by one and the light in
the room will be switched ON and when any one leaves the room then the counter is
decremented by one. The light will be only switched OFF until all the persons in the
room go out. The total number of persons inside the room is also displayed on the seven
segment displays.
P a g e | 5
The microcontroller does the above job. It receives the signals from the sensors, and this
signal is operated under the control of software which is stored in ROM. Microcontroller
AT89c2051 continuously monitor the LDR’s 1 & 2 (Light Dependent Resistor), When any
object pass through the LDR’s then the light falling on the LDR’s are obstructed , this
obstruction is sensed by microcontroller.
2.1COMPONENT LIST:
SL.NO EQUIPMENTS QTY SPECIFICATIONS MAKER’S
NAME
MAKER’S NO.
1 IC 1 AT89S52 (40 PIN) ATMEL 1D9662Aa0414B
2 7 SEGMENT LED 1 8 PIN ELECTROLITE _
3 CRYSTAL
OSCILLATOR
1 12MHz KDS 8J
4
TRANSISTOR 5 BC547 BR B E12
2 CL100 - -
5
CAPACITOR
1 10uF
KELTRON
_ 4 33pF
6 RESISTER 24 33K,8.2K,220K,1K _ _
7 VOLTAGE
REGULATOR
5 L7805 _ _
8 BREAD BOARD 5 PDC-20 PACIFIC _
9 SUPER
PROGRAMMER
1 SUPER PRO
MODEL 280U
XELTEX _
10 TIMER IC 5 NE555 _ _
P a g e | 6
2.3 BLOCK DIAGRAM :
P a g e | 7
3. TRANSMITTER AND RECEIVER SECTION
This section deals with the transmission of the light emitted by the two LEDs that we
have used and its reception by the sensors. The sensors that we have used are Photo
Diodes. The LEDs and the Photo Diodes are placed at the two opposite sides of the door.
The light emitted by the LEDs is continuously received by the photo diodes and once a
person enters the door the reception is hindered. Once the person crosses both sets of
LED and photo diodes present in front and back of the door, the counter is incremented
by 1. The counter gets incremented as long as people enter the door. Same thing
happens when people leave. Counter is decremented when light emitted by the LED at
the back of door is hindered first and then the one in front of the door.
LEDs Door
P a g e | 8
3.1 LED
Light emitting diodes, commonly called LEDs, are real unsung heroes in the electronics
world. They do dozens of different jobs and are found in all kinds of devices. Among
other things, they form numbers on digital clocks, transmit information from remote
controls, light up watches and tell you when your appliances are turned on. Collected
together, they can form images on a jumbo television screen or illuminate a traffic light.
Basically, LEDs are just tiny light bulbs that fit easily into an electrical circuit. But unlike
ordinary incandescent bulbs, they don't have a filament that will burn out, and they
don't get especially hot. They are illuminated solely by the movement of electrons in a
semiconductor material, and they last just as long as a standard transistor. The lifespan
of an LED surpasses the short life of an incandescent bulb by thousands of hours. Tiny
LEDs are already replacing the tubes that light up LCD HDTVs to make dramatically
thinner televisions
.
Now the thing is that, how a diode produces light?
Light is a form of energy that can be released by an atom. It is made up of many small
particle-like packets that have energy and momentum but no mass. These particles,
called photons, are the most basic units of light.
Photons are released as a result of moving electrons. In an atom, electrons move in
orbitals around the nucleus. Electrons in different orbitals have different amounts of
energy. Generally speaking, electrons with greater energy move in orbitals farther away
from the nucleus.For an electron to jump from a lower orbital to a higher orbital,
P a g e | 9
something has to boost its energy level. Conversely, an electron releases energy when it
drops from a higher orbital to a lower one. This energy is released in the form of a
photon. A greater energy drop releases a higher-energy photon, which is characterized
by a higher frequency.Free electrons moving across a diode can fall into empty holes
from the P-type layer. This involves a drop from the conduction band to a lower orbital,
so the electrons release energy in the form of photons. This happens in any diode, but
you can only see the photons when the diode is composed of certain material. The
atoms in a standard silicon diode, for example, are arranged in such a way that the
electron drops a relatively short distance. As a result, the photon's frequency is so low
that it is invisible to the human eye -- it is in the infrared portion of the light spectrum.
This isn't necessarily a bad thing, of course: Infrared LEDs are ideal for remote controls,
among other things
Visible light-emitting diodes (VLEDs), such as the ones that light up numbers in a digital
clock, are made of materials characterized by a wider gap between the conduction band
and the lower orbitals. The size of the gap determines the frequency of the photon -- in
other words, it determines the color of the light. While LEDs are used in everything from
remote controls to the digital displays on electronics, visible LEDs are growing in
popularity and use thanks to their long lifetimes and miniature size. Depending on the
materials used in LEDs, they can be built
to shine in infrared, ultraviolet, and all the
colors of the visible spectrum in between.
P a g e | 10
Infrared LEDs
An infrared light-emitting diode (LED) is a type of electronic device that emits infrared
light not visible to the naked eye. An infrared LED operates like a regular LED, but may
use different materials to produce infrared light. This infrared light may be used for a
remote control, to transfer data between devices, to provide illumination for night
vision equipment, or for a variety of other purposes.
An infrared LED is, like all LEDs, a type of diode, or simple semiconductor. Diodes are
designed so that electric current can only flow in one direction. As the current flows,
electrons fall from one part of the diode into holes on another part. In order to fall into
these holes, the electrons must shed energy in the form of photons, which produce
light.
The wavelength and color of the light produced depend on the material used in the
diode. Infrared LEDs use material that produces light in the infrared part of the
spectrum, that is, just below what the human eye can see. Different infrared LEDs may
produce infrared light of differing wavelengths, just like different LEDs produce light of
different colors.
A very common place to find an infrared LED is in a remote control for a television or
other device. One or more LEDs inside the remote transmit rapid pulses of infrared light
P a g e | 11
to a receiver on the television. The receiver then decodes and interprets these pulses as
a command and carries out the desired operation.
Infrared light can also be used to transfer data between electronic devices. Mobile
phones, personal digital assistants (PDAs), and some laptops may have an infrared LED
and receiver designed for short-range data transfer. Some wireless keyboards and
computer mice also use an infrared LED and receiver to replace a cable.
Although invisible to human eyes, many types of cameras and other sensors can see
infrared light. This makes infrared LED technology well-suited to applications like
security systems and night vision goggles. Many security cameras and camcorders use
infrared LEDs to provide a night-vision mode. Hunters may use similar equipment to
spot game at night, and some companies sell flashlights with an infrared LED to provide
extra illumination for night-vision cameras or devices.
Infrared LEDs can be used for a variety of other purposes. The U.S. Food and Drug
Administration has approved several products with infrared LEDs for use in medical or
cosmetic procedures. Robots may use an infrared LED to detect objects, and some utility
meters even have an infrared LED to transmit data to a tool for easy meter reading.
How are infrared LEDs different?
There are a couple key differences in the electrical characteristics of infrared LEDs
versus visible light LEDs. Infrared LEDs have a lower forward voltage, and a higher rated
current compared to visible LEDs. This is due to differences in the material properties of
the junction. A typical drive current for an infrared LED can be as high as 50 milliamps,
so dropping in a visible LED as a replacement for an infrared LED could be a problem
with some circuit designs.
IR LEDs aren’t rated in millicandelas, since their output isn’t visible (and candelas
measure light in a way weighted to the peak of the visible spectrum). They are usually
rated in milliwatts, and conversions to candelas aren’t especially meaningful.
P a g e | 12
LED Characteristics & Colours
There is a wide variety of different LEDs available on the market. The different LED
characteristics include colours light / radiation wavelength, light intensity, and a variety
of other LED characteristics.
The different LED characteristics have been brought about by a variety of factors, in the
manufacture of the LED. The semiconductor make-up is a factor, but fabrication
technology and encapsulation also play major part of the determination of the LED
characteristics.
LED colours
One of the major characteristics of an LED is its colour. Initially LED colours were very
restricted. For the first years only red LEDs were available.
However as semiconductor processes were improved and new research was undertaken
to investigate new materials for LEDs, different colours became available.
The diagram below shows some typical approximate curves for the voltages that may be
expected for different LED colours.
Typical (approximate) LED voltage curves
P a g e | 13
LED voltage drops
The voltage drop across an LED is different to that of a normal silicon LED. Typically the
LED voltage drop is between around 2 and 4 volts.
The actual LED voltage that appears across the two terminals is dependent mainly upon
the type of LED in question - the materials used.
As would be expected the LED voltage curve broadly follows that which would be
expected for the forward characteristic for a diode. However once the diode has turned
on, the voltage is relatively flat for a variety of forward current levels. This means that in
some cases designers have used them as very rough voltage stabilisers - zener diodes do
not operate at voltages as low as LEDs. However their performance is obviously
nowhere near as good.
LED Applications
What can you use LEDs for? Anything!
Automotive Applications With LEDs
Instrument Panels & Switches, Courtesy Lighting, CHMSL, Rear Stop/Turn/Tai, Retrofits,
New Turn/Tail/Marker Lights
Consumer Electronics & General Indication With LEDs
Household appliances, VCR/ DVD/ Stereo/Audio/Video devices, Toys/Games
Instrumentation, Security Equipment, Switches
Illumination With LEDs
Architectural Lighting, Signage (Channel Letters), Machine Vision, Retail Displays,
Emergency Lighting (Exit Signs), Neon and bulb Replacement, Flashlights, Accent
Lighting - Pathways, Marker Lights
P a g e | 14
Sign Applications With LEDs
Full Color Video, Monochrome Message Boards, Traffic/VMS, Transportation -
Passenger Information,
Signal Application With LEDs
Traffic, Rail, Aviation, Tower Lights, Runway Lights, Emergency/Police Vehicle Lighting,
Mobile Applications With LEDs
Mobile Phone, PDA's, Digital Cameras, Lap Tops, General Backlighting,
Photo Sensor Applications With LEDs
Medical Instrumentation, Bar Code Readers, Color & Money Sensors, Encoders, Optical
Switches, Fiber Optic Communication,
P a g e | 15
3.2 PHOTO DIODE
A photodiode is a type of photo detector capable of converting light into either current
or voltage, depending upon the mode of operation. The common, traditional solar cell
used to generate electric solar power is a large area photodiode.
Photodiodes are similar to regular semiconductor diodes except that they may be either
exposed (to detect vacuum UV or X-rays) or packaged with a window or optical fiber
connection to allow light to reach the sensitive part of the device. Many diodes
designed for use specifically as a photodiode use a PIN junction rather than a p-n
junction, to increase the speed of response. A photodiode is designed to operate in
reverse bias.
The material used to make a photodiode is critical to defining its properties, because
only photons with sufficient energy to excite electrons across the material's band gap
will produce significant photocurrents.
Materials commonly used to produce photodiodes include:
Material Electromagnetic spectrum
wavelength range (nm)
Silicon 190–1100
Germanium 400–1700
Indium gallium arsenide 800–2600
Lead(II) sulfide <1000–3500
Because of their greater band gap, silicon-based photodiodes generate less noise than
germanium-based photodiodes.
P a g e | 16
Features
Response of a silicon photo diode vs wavelength of the incident light
Critical performance parameters of a photodiode include:
Responsivity
The ratio of generated photocurrent to incident light power, typically expressed in
A/W when used in photoconductive mode. The responsivity may also be
expressed as a Quantum efficiency, or the ratio of the number of photogenerated
carriers to incident photons and thus a unitless quantity.
Dark current
The current through the photodiode in the absence of light, when it is operated in
photoconductive mode. The dark current includes photocurrent generated by
background radiation and the saturation current of the semiconductor junction.
Dark current must be accounted for by calibration if a photodiode is used to make
an accurate optical power measurement, and it is also a source of noise when a
photodiode is used in an optical communication system.
P a g e | 17
Noise-equivalent power
(NEP) The minimum input optical power to generate photocurrent, equal to the
rms noise current in a 1 hertz bandwidth. The related characteristic detectivity (D)
is the inverse of NEP, 1/NEP; and the specific detectivity ( ) is the detectivity
normalized to the area (A) of the photodetector, . The NEP is roughly
the minimum detectable input power of a photodiode.
When a photodiode is used in an optical communication system, these parameters
contribute to the sensitivity of the optical receiver, which is the minimum input power
required for the receiver to achieve a specified bit error rate.
Comparison with photomultipliers
Advantages compared to photomultipliers:
1. Excellent linearity of output current as a function of incident light
2. Spectral response from 190 nm to 1100 nm (silicon), longer wavelengths with
other semiconductor materials
3. Low noise
4. Ruggedized to mechanical stress
5. Low cost
6. Compact and light weight
7. Long lifetime
8. High quantum efficiency, typically 80%
9. No high voltage required
Disadvantages compared to photomultipliers:
1. Small area
2. No internal gain (except avalanche photodiodes, but their gain is typically 102–10
3
compared to up to 108 for the photomultiplier)
3. Much lower overall sensitivity
4. Photon counting only possible with specially designed, usually cooled
photodiodes, with special electronic circuits
5. Response time for many designs is slower
P a g e | 18
Photodiode array
A one-dimensional array of hundreds or thousands of photodiodes can be used as a
position sensor, for example as part of an angle sensor.[8]
One advantage of photodiode
arrays (PDAs) is that they allow for high speed parallel read out since the driving
electronics may not be built in like a traditional CMOS or CCD sensor.
Principle of operation
A photodiode is a p-n junction or PIN structure. When a photon of sufficient energy
strikes the diode, it excites an electron, thereby creating a free electron (and a positively
charged electron hole). This mechanism is also known as the inner photoelectric effect.
If the absorption occurs in the junction's depletion region, or one diffusion length away
from it, these carriers are swept from the junction by the built-in field of the depletion
region. Thus holes move toward the anode, and electrons toward the cathode, and a
photocurrent is produced. This photocurrent is the sum of both the dark current
(without light) and the light current, so the dark current must be minimized to enhance
the sensitivity of the device.
Photovoltaic mode
When used in zero bias or photovoltaic mode, the flow of photocurrent out of the
device is restricted and a voltage builds up. This mode exploits the photovoltaic effect,
which is the basis for solar cells – a traditional solar cell is just a large area photodiode.
Photoconductive mode
In this mode the diode is often reverse biased (with the cathode positive), dramatically
reducing the response time at the expense of increased noise. This increases the width
of the depletion layer, which decreases the junction's capacitance resulting in faster
response times. The reverse bias induces only a small amount of current (known as
saturation or back current) along its direction while the photocurrent remains virtually
the same. For a given spectral distribution, the photocurrent is linearly proportional to
the luminance (and to the irradiance).
P a g e | 19
Although this mode is faster, the photoconductive mode tends to exhibit more
electronic noise. The leakage current of a good PIN diode is so low (<1 nA) that the
Johnson–Nyquist noise of the load resistance in a typical circuit often dominates.
Other modes of operation
Avalanche photodiodes have a similar structure to regular photodiodes, but they are
operated with much higher reverse bias. This allows each photo-generated carrier to be
multiplied by avalanche breakdown, resulting in internal gain within the photodiode,
which increases the effective responsivity of the device.
A phototransistor is in essence a bipolar transistor encased in a transparent case so that
light can reach the base-collector junction. It was invented by Dr. John N. Shive (more
famous for his wave machine) at Bell Labs in 1950. The electrons that are generated by
photons in the base-collector junction are injected into the base, and this photodiode
current is amplified by the transistor's current gain β (or hfe). If the emitter is left
unconnected, the phototransistor becomes a photodiode. While phototransistors have
a higher responsivity for light they are not able to detect low levels of light any better
than photodiodes. Phototransistors also have significantly longer response times.
I-V curve of a photodiode and the equivalent circuit
P a g e | 20
Applications
P-N photodiodes are used in similar applications to other photo detectors, such as
photoconductors, charge-coupled devices, and photomultiplier tubes. They may be used
to generate an output which is dependent upon the illumination (analog; for
measurement and the like), or to change the state of circuitry (digital; either for control
and switching, or digital signal processing).
Photodiodes are used in consumer electronics devices such as compact disc players,
smoke detectors, and the receivers for infrared remote control devices used to control
equipment from televisions to air conditioners. For many applications either
photodiodes or photoconductors may be used. Either type of photo sensor may be used
for light measurement, as in camera light meters, or to respond to light levels, as in
switching on street lighting after dark.
Photosensors of all types may be used to respond to incident light, or to a source of light
which is part of the same circuit or system. A photodiode is often combined into a single
component with an emitter of light, usually a light-emitting diode (LED), either to detect
the presence of a mechanical obstruction to the beam (slotted optical switch), or to
couple two digital or analog circuits while maintaining extremely high electrical isolation
between them, often for safety (optocoupler).
Photodiodes are often used for accurate measurement of light intensity in science and
industry. They generally have a more linear response than photoconductors.
They are also widely used in various medical applications, such as detectors for
computed tomography (coupled with scintillators), instruments to analyze samples
(immunoassay), and pulse oximeters.
PIN diodes are much faster and more sensitive than p-n junction diodes, and hence are
often used for optical communications and in lighting regulation.
P-N photodiodes are not used to measure extremely low light intensities. Instead, if high
sensitivity is needed, avalanche photodiodes, intensified charge-coupled devices or
photomultiplier tubes are used for applications such as astronomy, spectroscopy, night
vision equipment and laser range finding.
P a g e | 21
3.3 TRANSMISSION AND RECEIVING SYSTEM
The LEDs and the Photo Diodes together constitute the transmission & receiving system.
The LEDs are placed at one end of the door and the Photo Diodes are placed at the
other end of the door both in front and back end of the door. Light is transmitted by the
LEDs which is then received by the Photo Diodes at the other end of the door.
LEDs Door
3.4 HOW THE VISITOR IS SENSED
The LEDs and the Photo Diodes are placed at the two opposite sides of the door. The
light emitted by the LEDs is continuously received by the photo diodes and once a
person enters the door the reception is hindered. Once the person crosses both sets of
LED and photo diodes present in front and back of the door, the counter is incremented
by 1. Lights are then automatically switched on. The counter gets incremented as long
as people enter the door. Same thing happens when people leave. Counter is
decremented when light emitted by the LED at the back of door is hindered first and
then the one in front of the door. As soon as the counter value reaches 0, the circuit
opens and the lights are automatically switched off. The count of the number of visitors
is shown on 7-segment LCD attached to the circuit.
P a g e | 22
4. MULTIVIBRATOR
A multivibrator is an electronics ckt which will be used as timer. This ckt is formed by
555 timer or simple transistor logic. There are three types of multivibrator – Astable,
monostable and bistable.
This multivibrator circuit oscillates between a "HIGH" state and a "LOW" state producing
a continuous output. Astable multivibrators generally have an even 50% duty cycle, that
is that 50% of the cycle time the output is "HIGH" and the remaining 50% of the cycle
time the output is "OFF". In other words, the duty cycle for an astable timing pulse is
1:1.
Sequential logic circuits that use the clock signal for synchronization are dependant
upon the frequency and and clock pulse width to activate there switching action.
Sequential circuits may also change their state on either the rising or falling edge, or
both of the actual clock signal as we have seen previously with the basic flip-flop
circuits. The following list are terms associated with a timing pulse or waveform.
Active HIGH - if the state changes occur at the
clock's rising edge or during the clock width.
Clock Signal Waveform
Active LOW - if the state changes occur at the
clock's falling edge.
Duty Cycle - is the ratio of clock width and clock
period.
Clock Width - this is the time during which the value of the clock signal is equal to one.
Clock Period - this is the time between successive transitions in the same direction,
i.e., between two rising or two falling edges.
Clock Frequency - the clock frequency is the reciprocal of the clock period, frequency =
P a g e | 23
1/clock period
Clock pulse generation circuits can be a combination of analogue and digital circuits that
produce a continuous series of pulses (these are called astable multivibrators) or a pulse
of a specific duration (these are called monostable multivibrators). Combining two or
more of multivibrators provides generation of a desired pattern of pulses (including
pulse width, time between pulses and frequency of pulses).
There are basically three types of clock pulse generation circuits:
• Astable - A free-running multivibrator that has NO stable states but switches
continuously between two states this action produces a train of square wave
pulses at a fixed frequency.
•
• Monostable - A one-shot multivibrator that has only ONE stable state and is
triggered externally with it returning back to its first stable state.
•
• Bistable - A flip-flop that has TWO stable states that produces a single pulse either
positive or negative in value.
One way of producing a very simple clock signal is by the interconnection of logic gates.
As NAND gates contains amplification, they can also be used to provide a clock signal or
timing pulse with the aid of a single Capacitor, C and Resistor, R which provide the
feedback and timing function. These timing circuits are often used because of there
simplicity and are also useful if a logic circuit is designed that has un-used gates which
can be utilised to create the monostable or astable oscillator. This simple type of RC
Oscillator network is sometimes called a "Relaxation Oscillator".
Monostable Circuits.
Monostable Multivibrators or "one-shot" pulse generators are used to convert short
sharp pulses into wider ones for timing applications. Monostable multivibrators
generate a single output pulse, either "high" or "low", when a suitable external trigger
signal or pulse T is applied. This trigger pulse signal initiates a timing cycle which causes
the output of the monostable to change state at the start of the timing cycle, (t1) and
remain in this second state until the end of the timing period, (t1) which is determined
by the time constant of the timing capacitor, CT and the resistor, RT.
P a g e | 24
The monostable multivibrator now stays in this second timing state until the end of the
RC time constant and automatically resets or returns itself back to its original (stable)
state. Then, a monostable circuit has only one stable state. A more common name for
this type of circuit is simply a "Flip-Flop" as it can be made from two cross-coupled
NAND gates (or NOR gates) as we have seen previously. Consider the circuit below.
Simple NAND Gate Monostable Circuit
Suppose that initially the trigger input T is held HIGH at logic level "1" by the resistor R1
so that the output from the first NAND gate U1 is LOW at logic level "0", (NAND gate
principals). The timing resistor, RT is connected to a voltage level equal to logic level "0",
which will cause the capacitor, CT to be discharged. The output of U1 is LOW, timing
capacitor CT is completely discharged therefore junction V1 is also equal to "0" resulting
in the output from the second NAND gate U2, which is connected as an inverting NOT
gate will therefore be HIGH.
The output from the second NAND gate, (U2) is fed back to one input of U1 to provide
the necessary positive feedback. Since the junction V1 and the output of U1 are both at
logic "0" no current flows in the capacitor CT. This results in the circuit being Stable and
it will remain in this state until the trigger input T changes.
If a negative pulse is now applied either externally or by the action of the push-button
to the trigger input of the NAND gate U1, the output of U1 will go HIGH to logic "1"
(NAND gate principles). Since the voltage across the capacitor cannot change
instantaneously (capacitor charging principals) this will cause the junction at V1 and also
the input to U2 to also go HIGH, which inturn will make the output of the NAND gate U2
change LOW to logic "0" The circuit will now remain in this second state even if the
trigger input pulse T is removed. This is known as the Meta-stable state.
P a g e | 25
The voltage across the capacitor will now increase as the capacitor CT starts to charge up
from the output of U1 at a time constant determined by the resistor/capacitor
combination. This charging process continues until the charging current is unable to
hold the input of U2 and therefore junction V1 HIGH. When this happens, the output of
U2 switches HIGH again, logic "1", which inturn causes the output of U1 to go LOW and
the capacitor discharges into the output of U1 under the influence of resistor RT. The
circuit has now switched back to its original stable state.
Thus for each negative going trigger pulse, the monostable multivibrator circuit
produces a LOW going output pulse. The length of the output time period is determined
by the capacitor/resistor combination (RC Network) and is given as the Time Constant
T = 0.69RC of the circuit in seconds. Since the input impedance of the NAND gates is
very high, large timing periods can be achieved.
As well as the NAND gate monostable type circuit above, it is also possible to build
simple monostable timing circuits that start their timing sequence from the rising-edge
of the trigger pulse using NOT gates, NAND gates and NOR gates connected as inverters
as shown below.
NOT Gate Monostable Circuit
As with the NAND gate circuit above, initially the trigger input T is HIGH at a logic level
"1" so that the output from the first NOT gate U1 is LOW at logic level "0". The timing
resistor, RT and the capacitor, CT are connected together in parallel and also to the input
of the second NOT gate U2. As the input to U2 is LOW at logic "0" its output at Q is HIGH
at logic "1".
P a g e | 26
When a logic level "0" pulse is applied to the trigger input T of the first NOT gate it
changes state and produces a logic level "1" output. The diode D1 passes this logic "1"
voltage level to the RC timing network. The voltage across the capacitor, CT increases
rapidly to this new voltage level, which is also connected to the input of the second NOT
gate. This inturn outputs a logic "0" at Q and the circuit stays in this Meta-stable state as
long as the trigger input T applied to the circuit remains LOW.
When the trigger signal returns HIGH, the output from the first NOT gate goes LOW to
logic "0" (NOT gate principals) and the fully charged capacitor, CT starts to discharge
itself through the parallel resistor, RT connected across it. When the voltage across the
capacitor drops below the lower threshold value of the input to the second NOT gate, its
output switches back again producing a logic level "1" at Q. The diode D1 prevents the
timing capacitor from discharging itself back through the first NOT gates output.
Then, the Time Constant for a NOT gate Monostable Multivibrator is given as
T = 0.8RC + Trigger in seconds.
One main disadvantage of Monostable Multivibrators is that the time between the
application of the next trigger pulse T has to be greater than the RC time constant of the
circuit.
Astable Circuits.
Astable Multivibrators are a type of free running oscillator that have no permanent
"meta" or "steady" state but are continually changing there output from one state
("LOW") to the other state ("HIGH") and then back again. This continual switching action
from "HIGH" to "LOW" and "LOW" to "HIGH" produces a continuous and stable square
wave output that switches abruptly between the two logic levels making it ideal for
timing and clock pulse applications. As with the monostable multivibrator circuit above,
the timing cycle is determined by the time constant of the resistor-capacitor, RC
Network. Then the output frequency can be varied by changing the value(s) of the
resistors and capacitor in the circuit.
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NAND Gate Astable Multivibrators
The astable multivibrator circuit uses two CMOS NOT gates such as the CD4069 or the
74HC04 hex inverter ICs, or as in our simple circuit below a pair of CMOS NAND such as
the CD4011 or the 74LS132 and an RC timing network. The two NAND gates are
connected as inverting NOT gates.
Suppose that initially the output from the NAND gate U2 is HIGH at logic level "1", then
the input must therefore be LOW at logic level "0" (NAND gate principles) as will be the
output from the first NAND gate U1. Capacitor, C is connected between the output of
the second NAND gate U2 and its input via the timing resistor, R2. The capacitor now
charges up at a rate determined by the time constant of R2 and C.
As the capacitor, C charges up, the junction between the resistor R2 and the capacitor, C,
which is also connected to the input of the NAND gate U1 via the stabilizing resistor, R2
decreases until the lower threshold value of U1 is reached at which point U1 changes
state and the output of U1 now becomes HIGH. This causes NAND gate U2 to also
change state as its input has now changed from logic "0" to logic "1" resulting in the
output of NAND gate U2 becoming LOW, logic level "0".
Capacitor C is now reverse biased and discharges itself through the input of NAND gate
U1. Capacitor, C charges up again in the opposite direction determined by the time
constant of both R2 and C as before until it reaches the upper threshold value of NAND
gate U1. This causes U1 to change state and the cycle repeats itself over again.
Then, the time constant for a NAND gate Astable Multivibrator is given as T = 2.2RC in
seconds with the output frequency given as f = 1/T.
For example: if resistor R2 = 10kΩ and the capacitor C = 45nF, then the oscillation
frequency will be given as:
P a g e | 28
then the output frequency is calculated as being 1kHz, which equates to a time constant
of 1mS so the output waveform would look like:
Bistable Circuits.
The Bistable Multivibrators circuit is basically a SR flip-flop that we look at in the
previous tutorials with the addition of an inverter or NOT gate to provide the necessary
switching function. As with flip-flops, both states of a bistable multivibrator are stable,
and the circuit will remain in either state indefinitely. This type of multivibrator circuit
passes from one state to the other "only" when a suitable external trigger pulse T is
applied and to go through a full "SET-RESET" cycle two triggering pulses are required.
This type of circuit is also known as a "Bistable Latch", "Toggle Latch" or simply "T-
latch".
NAND Gate Bistable Multivibrator
The simplest way to make a Bistable Latch is to connect together a pair of Schmitt
NAND gates to form a SR latch as shown above. The two NAND gates, U2 and U3 form
P a g e | 29
the bistable which is triggered by the input NAND gate, U1. This U1 NAND gate can be
omitted and replaced by a single toggle switch to make a switch debounce circuit as
seen previously in the SR Flip-flop tutorial. When the input pulse goes "LOW" the
bistable latches into its "SET" state, with its output at logic level "1", until the input goes
"HIGH" causing the bistable to latch into its "RESET" state, with its output at logic level
"0". The output of a bistable multivibrator will stay in this "RESET" state until another
input pulse is applied and the whole sequence will start again.
Then a Bistable Latch or "Toggle Latch" is a two-state device in which both states either
positive or negative, (logic "1" or logic "0") are stable.
Bistable Multivibrators have many applications such as frequency dividers, counters or
as a storage device in computer memories but they are best used in circuits such as
Latches and Counters.
555 Timer Circuit.
Simple Monostable or Astable timing circuits can now be easily made using standard
waveform generator IC's in the form of relaxation oscillators by connecting a few
passive components to their inputs with the most commonly used waveform generator
type IC being the classic 555 timer.
The 555 Timer is a very versatile low cost timing IC that can produce a very accurate
timing periods with good stability of around 1% and which has a variable timing period
from between a few micro-seconds to many hours with the timing period being
controlled by a single RC network connected to a single positive supply of between 4.5
and 16 volts. The NE555 timer and its successors, ICM7555, CMOS LM1455, DUAL NE556
etc, are covered in the 555 Oscillator tutorial and other good electronics based
websites, so are only included here for reference purposes as a clock pulse generator.
The 555 connected as an Astable oscillator is given below.
Using 555 timer(three 5 kohm resistors) and opamp(comparator) logic we can generate
timer output. 555 IC has 8 pins-Gnd, Trigger, output, reset, control, threshold, discharge
and vcc. The 555 timer IC is an integrated circuit (chip) used in a variety of timer, pulse
P a g e | 30
generation, and oscillator applications. The 555 can be used to provide time delays, as
an oscillator, and as a flip-flop element. Derivatives provide up to four timing circuits in
one package.
Introduced in 1971 by Signetics, the 555 is still in widespread use, thanks to its ease of
use, low price, and good stability. It is now made by many companies in the original
bipolar and also in low-power CMOS types. As of 2003, it was estimated that 1 billion
units are manufactured every year.
555 IC pin diagram
P a g e | 31
555IC schematic diagram
DESCRIPTION
The 555 monolithic timing circuit is a highly stable controller capable of producing
accurate time delays, or oscillation. In the time delay mode of operation, the time is
precisely controlled by one external resistor and capacitor. For a stable operation as an
oscillator, the free running frequency and the duty cycle are both accurately controlled
with two external resistors and one capacitor. The circuit may be triggered and reset on
falling waveforms, and the output structure can source or sink up to 200mA.
FEATURES
• Turn-off time less than 2ms
• Max. operating frequency greater than 500kHz
• Timing from microseconds to hours
• Operates in both astable and monostable modes
• High output current
P a g e | 32
• Adjustable duty cycle
• TTL compatible
• Temperature stability of 0.005% per °C
APPLICATIONS
• Precision timing
• Pulse generation
• Sequential timing
• Time delay generation
• Pulse width modulation
P a g e | 33
P a g e | 34
4.1 TYPE OF MULTIVIBRATOR
Here we use monostable multivibrator. Monostable Multivibrator is also called one shot
Multivibrator. Trigger is needed here. We can give negative edge triggering. It has one
stable state; may be 0 or 1 and has one quasi stable state.
P a g e | 35
4.2 OPERATION OF MONOSTABLE MULTIVIBRATOR
Monostable mode: in this mode, the 555 functions as a "one-shot" pulse generator.
Applications include timers, missing pulse detection, bounce free switches, touch
switches, frequency divider, capacitance measurement, pulse-width modulation (PWM)
and so on.
Monostable Multivibrator
The monostable multivibrator (sometimes called a ONE-SHOT MULTIVIBRATOR) is a
square- or rectangular-wave generator with just one stable condition. With no input
signal (quiescent condition) one amplifier conducts and the other is in cutoff. The
monostable multivibrator is basically used for pulse stretching. It is used in computer
logic systems and communication navigation equipment. The operation of the
monostable multivibrator is relatively simple. The input is triggered with a pulse of
voltage. The output changes from one voltage level to a different voltage level. The
output remains at this new voltage level for a definite period of time. Then the circuit
automatically reverts to its original condition and remains that way until another trigger
pulse is applied to the input. The monostable multivibrator actually takes this series of
input triggers and converts them to uniform square pulses. All of the square output
pulses are of the same amplitude and time duration
Schematic Diagram Of Multivibrator
P a g e | 36
Block Diagram of Monostable Multivibrator
Initially, when the output at pin 3 is low i.e. the circuit is in a stable state, the transistor
is on and capacitor- C is shorted to ground. When a negative pulse is applied to pin 2,
the trigger input falls below +1/3 VCC, the output of comparator goes high which resets
the flip-flop and consequently the transistor turns off and the output at pin 3 goes high.
This is the transition of the output from stable to quasi-stable state, as shown in figure.
As the discharge transistor is cut¬off, the capacitor C begins charging toward +VCC
through resistance RA with a time constant equal to RAC. When the increasing capacitor
voltage becomes slightly greater than +2/3 VCC, the output of comparator 1 goes high,
P a g e | 37
which sets the flip-flop. The transistor goes to saturation, thereby discharging the
capacitor C and the output of the timer goes low, as illustrated in figure.
Thus the output returns back to stable state from quasi-stable state.
The output of the Monostable Multivibrator remains low until a trigger pulse is again
applied. Then the cycle repeats. Trigger input, output voltage and capacitor voltage
waveforms are shown in figure.
Monostable Multivibrator Designing
The capacitor C has to charge through resistance RA. The larger the time constant RAC,
the longer it takes for the capacitor voltage to reach +2/3VCC.
In other words, the RC time constant controls the width of the output pulse. The time
during which the timer output remains high.
tp = 1.0986 RAC
where RA is in ohms and C is in farads. The above relation is derived as below.
Voltage across the capacitor at any instant during charging period is given as
vc = VCC (1- e-t/RAC)
Substituting vc = 2/3 VCC in above equation we get the time taken by the capacitor to
charge from 0 to +2/3VCC.
So +2/3VCC. = VCC. (1 – e-t/RAC) or t – RAC loge 3 = 1.0986 RAC
So pulse width, tP = 1.0986 RAC s 1.1 RAC
P a g e | 38
Output wave form of monostable multivibrator
Transmitter Circuit:
Transmission Ckt Using Monostable Multivibrtor
P a g e | 39
IR transmission circuit is used to generate the modulated 36 KHZ IR signal. The IC 555
timer in the transmitter side is to generate 36 KHZ square signal. Adjust the preset in the
transmitter to get 38 KHZ signal in the output. Around 1.4k we get 38 KHZ signal. Then
you point it over the sensor and output will go low when it senses IR signal of 38 KHZ.
Receiver Circuit:
The IR will emit modulated 38 KHZ IR signal and in receiver we use TSOP1738 Infrared
sensor.Output goes high when there is an interruption and it return back to low after
the time time period determined by the capacitor and resistor in the circuit i,e around 1
second.Input is given to the port 1 of microcontroller.Port 0 is used for seven segment display
unit.Port 2 is used for relay turn on turn of.
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5.MICROCONTROLLER
GENERAL OVERVIEW OF 8085 MICROPROCESSOR ARCHITECTURE:
1. The microprocessor can be programmed to perform functions on given data by
writing specific instructions into its memory.
2. The microprocessor reads one instruction at a time, matches it with its instruction
set, and performs the data manipulation specified.
3. The result is either stored back into memory or displayed on an output device.
4. The 8085 is an 8-bit general purpose microprocessor that can address 64K Byte of
memory.
5. It has 40 pins and uses +5V for power. It can run at a maximum frequency of 3
MHz.
6. The pins on the chip can be grouped into 6 groups:
i. Address Bus.
ii. Data
iii. Control and Status Signals.
iv. Power supply and frequency.
v. Externally Initiated Signals.
vi. Serial I/O ports.
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COMPARISON BETWEEN 8085 AND 8051:
The main differences between microprocessor and microcontroller are the following-
i. By microprocessor is meant the general purpose microprocessor such as Intel’s
x86 family(8085,8086,80286 and the Pentium)or Motorola’s 680x0
family(68000,68020 etc).
ii. These Microprocessor contain no RAM ,no ROM ,and no I/O ports on the chip
itself. For this reason ,they are commonly refer to as general-purpose
microprocessors.
A microcontroller has a CPU(a microprocessor)in addition to a fixed
amount of RAM,ROM,I/O ports and controllers.
Difference between 8051 and 8951
Instruction set, Internal memory structure and Pinout are the same. 8951 Controllers
which are faster and more complex were first developed in the 90's as an improvement
to the 8051.
Many 8951 controllers have 2, 4 or 6 clock cores as opposed to 12. Whats more many
provide onboard DAC, ADC, I2C, USB, CAN etc
5.1WORKING PRINCIPLE
8051 Microcontroller is a programable device which is used for controlling purpose.
Basically 8051 controller is Mask porogramble means it will programed at the time of
manufacturing and will not programed again, there is a derivative of 8051
microcontroller, 89c51 microcontroller which is reprogramable upto 10000 times, here
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is small discription abot the 89c51 microcontroller.
It have 4 ports which are used as input or output according to your need.
These prots are also programmed as bit wise pattern, means you can use each bit of
microcontroller saperatelly as input or output.
This 89c51 is 8-bit device mean each port have 8-bits for I/O, total of 32-bits in the
controller.
This device also have Timer, Serial Port interface and Interrupt controlling you can use
these according to your need.
This device have 4K of ROM space to store the program,and 256Bytes of RAM space,
this device have ability to interface with TTL based devices and also with the external
MEMORY to increase its data space, but when your are using external MEMORY the 2
ports of 89c51 microcontroller are used for this purpose.
The Microcontroller that we have used in this project is AT89C51. AT89C51 is an 8-bit
microcontroller and belongs to Atmel's 8051 family. ATMEL 89C51 has 4KB of Flash
programmable and erasable read only memory (PEROM) and 128 bytes of RAM. It can
be erased and program to a maximum of 1000 times.
In 40 pin AT89C51, there are four ports designated as P1, P2, P3 and P0. All these ports
are 8-bit bi-directional ports, i.e., they can be used as both input and output ports.
Except P0 which needs external pull-ups, rest of the ports have internal pull-ups. When
1s are written to these port pins, they are pulled high by the internal pull-ups and can be
used as inputs. These ports are also bit addressable and so their bits can also be
accessed individually.
Port P0 and P2 are also used to provide low byte and high byte addresses, respectively,
when connected to an external memory. Port 3 has multiplexed pins for special
functions like serial communication, hardware interrupts, timer inputs and read/write
operation from external memory. AT89C51 has an inbuilt UART for serial
communication. It can be programmed to operate at different baud rates. Including two
timers & hardware interrupts, it has a total of six interrupts.
P a g e | 43
Pin Diagram
P a g e | 44
Pin No Function Name
1
8 bit input/output port (P1) pins
P1.0
2 P1.1
3 P1.2
4 P1.3
5 P1.4
6 P1.5
7 P1.6
8 P1.7
9 Reset pin; Active high Reset
10 Input (receiver) for serial communication RxD
8 bit
input/output
port (P3)
pins
P3.0
11 Output (transmitter) for serial communication TxD P3.1
12 External interrupt 1 Int0 P3.2
13 External interrupt 2 Int1 P3.3
14 Timer1 external input T0 P3.4
15 Timer2 external input T1 P3.5
16 Write to external data memory Write P3.6
17 Read from external data memory Read P3.7
18 Quartz crystal oscillator (up to 24 MHz)
Crystal 2
19 Crystal 1
20 Ground (0V) Ground
21
8 bit input/output port (P2) pins
/
High-order address bits when interfacing with external memory
P2.0/ A8
22 P2.1/ A9
23 P2.2/ A10
24 P2.3/ A11
25 P2.4/ A12
26 P2.5/ A13
27 P2.6/ A14
28 P2.7/ A15
29 Program store enable; Read from external program memory PSEN
30 Address Latch Enable ALE
Program pulse input during Flash programming Prog
31 External Access Enable; Vcc for internal program executions EA
Programming enable voltage; 12V (during Flash programming) Vpp
32
8 bit input/output port (P0) pins
Low-order address bits when interfacing with external memory
P0.7/ AD7
33 P0.6/ AD6
34 P0.5/ AD5
35 P0.4/ AD4
36 P0.3/ AD3
37 P0.2/ AD2
38 P0.1/ AD1
39 P0.0/ AD0
40 Supply voltage; 5V (up to 6.6V) Vcc
P a g e | 45
Description
The AT89S52 is a low-power, high-performance CMOS 8-bit microcontroller with 8K
bytes of in-system programmable Flash memory. The device is manufactured using
Atmel’s high-density non volatile memory technology and is compatible with the
industry-standard 80C51 instruction set and pin out. The on-chip Flash allows the
program memory to be reprogrammed in-system or by a conventional non volatile
memory programmer.
By combining a versatile 8-bit CPU with in-system programmable Flash on a monolithic
chip, the Atmel AT89S52 is a powerful microcontroller which provides a highly-flexible
and cost-effective solution to many embedded control applications. The AT89S52
provides the following standard features: 8K bytes of Flash, 256 bytes of RAM, 32 I/O
lines, Watchdog timer, two data pointers, three 16-bit timer/counters, a six-vector two-
level interrupt architecture, a full duplex serial port, on-chip oscillator, and clock
circuitry. In addition, the AT89S52 is designed with static logic for operation down to
zero frequency and supports two software selectable power saving modes. The Idle
Mode stops the CPU while allowing the RAM, timer/counters, serial port, and interrupt
system to continue functioning. The Power-down mode saves the RAM contents but
freezes the oscillator, disabling all other chip functions until the next interrupt or
hardware reset.
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BLOCK DIAGRAM
P a g e | 47
PIN DESCRIPTION
VCC
Supply voltage.
GND
Ground.
Port 0
Port 0 is an 8-bit open drain bidirectional I/O port. As an output port, each pin can sink
eight TTL inputs. When 1s are written to port 0 pins, the pins can be used as high-
impedance inputs.
Port 0 can also be configured to be the multiplexed low-order address/data bus during
accesses to external program and data memory. In this mode, P0 has internal pullups.
Port 0 also receives the code bytes during Flash programming and outputs the code
bytes during program verification. External pullups are required during program
verification.
Port 1
Port 1 is an 8-bit bidirectional I/O port with internal pullups. The Port 1 output buffers
can sink/source four TTL inputs. When 1s are written to Port 1 pins, they are pulled high
by the internal pullups and can be used as inputs. As inputs, Port 1 pins that are
externally being pulled low will source current (IIL) because of the internal pullups.
In addition, P1.0 and P1.1 can be configured to be the timer/counter 2 external count
input (P1.0/T2) and the timer/counter 2 trigger input (P1.1/T2EX), respectively, as
shown in the following table.
Port 1 also receives the low-order address bytes during Flash programming and
verification.
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Port Pin Alternate Functions
P1.0 T2 (external count input to
Timer/Counter 2), clock-out
P1.1 T2EX (Timer/Counter 2
capture/reload trigger and
direction control)
P1.5 MOSI (used for In-System
Programming)
P1.6 MISO (used for In-System
Programming)
P1.7 SCK (used for In-System
Programming)
Port 2
Port 2 is an 8-bit bidirectional I/O port with internal pullups. The Port 2 output buffers
can sink/source four TTL inputs. When 1s are written to Port 2 pins, they are pulled high
by the internal pullups and can be used as inputs. As inputs, Port 2 pins that are
externally being pulled low will source current (IIL) because of the internal pullups.
Port 2 emits the high-order address byte during fetches from external program memory
and during accesses to external data memory that use 16-bit addresses (MOVX @
DPTR). In this application, Port 2 uses strong internal pul-lups when emitting 1s. During
accesses to external data memory that use 8-bit addresses (MOVX @ RI), Port 2 emits
the contents of the P2 Special Function Register.
Port 2 also receives the high-order address bits and some control signals during Flash
programming and verification.
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Port 3
Port 3 is an 8-bit bidirectional I/O port with internal pullups. The Port 3 output buffers
can sink/source four TTL inputs. When 1s are written to Port 3 pins, they are pulled high
by the internal pullups and can be used as inputs. As inputs, Port 3 pins that are
externally being pulled low will source current (IIL) because of the pullups.
Port 3 also serves the functions of various special features of the AT89S52, as shown in
the following table.
Port 3 also receives some control signals for Flash programming and verification.
Port Pin Alternate Functions
P3.0 RXD (serial input port)
P3.1 TXD (serial output port)
P3.2 INT0 (external interrupt 0)
P3.3 INT1 (external interrupt 1)
P3.4 T0 (timer 0 external input)
P3.5 T1 (timer 1 external input)
P3.6 WR (external data memory write
strobe)
P3.7 RD (external data memory read
strobe)
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RST
Reset input. A high on this pin for two machine cycles while the oscillator is running
resets the device. This pin drives High for 96 oscillator periods after the Watchdog times
out. The DISRTO bit in SFR AUXR (address 8EH) can be used to disable this feature. In the
default state of bit DISRTO, the RESET HIGH out feature is enabled.
ALE/PROG
Address Latch Enable (ALE) is an output pulse for latching the low byte of the address
during accesses to external memory. This pin is also the program pulse input (PROG)
during Flash programming.
In normal operation, ALE is emitted at a constant rate of 1/6 the oscillator frequency
and may be used for external timing or clocking purposes. Note, however, that one ALE
pulse is skipped during each access to external data memory.
If desired, ALE operation can be disabled by setting bit 0 of SFR location 8EH. With the
bit set, ALE is active only during a MOVX or MOVC instruction. Otherwise, the pin is
weakly pulled high. Setting the ALE-disable bit has no effect if the microcontroller is in
external execution mode.
PSEN
Program Store Enable (PSEN) is the read strobe to external program memory.
When the AT89S52 is executing code from external program memory, PSEN is activated
twice each machine cycle, except that two PSEN activations are skipped during each
access to external data memory.
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EA/VPP
External Access Enable. EA must be strapped to GND in order to enable the device to
fetch code from external program memory locations starting at 0000H up to FFFFH.
Special Function Registers
A map of the on-chip memory area called the Special Function Register (SFR) space is
shown in Table 1.
Note that not all of the addresses are occupied, and unoccupied addresses may not be
implemented on the chip. Read accesses to these addresses will in general return
random data, and write accesses will have an indeterminate effect.
User software should not write 1s to these unlisted locations, since they may be used in
future products to invoke new features. In that case, the reset or inactive values of the
new bits will always be 0.
Timer 2 Registers:
Control and status bits are contained in registers T2CON (shown in Table 2) and T2MOD
(shown in Table 3) for Timer 2.
The register pair (RCAP2H, RCAP2L) are the Capture/Reload registers for Timer 2 in 16-
bit capture mode or 16-bit auto-reload mode.
Interrupt Registers:
The individual interrupt enable bits are in the IE register. Two priorities can be set for
each of the six interrupt sources in the IP register.
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Dual Data Pointer Registers:
To facilitate accessing both internal and external data memory, two banks of 16-bit Data
Pointer Registers are provided: DP0 at SFR address locations 82H-83H and DP1 at 84H-
85H. Bit DPS = 0
in SFR AUXR1 selects DP0 and DPS = 1 selects DP1.
Memory Organization
MCS-51 devices have a separate address space for Program and Data Memory. Up to
64K bytes each of external Program and Data Memory can be addressed.
Program Memory
If the EA pin is connected to GND, all program fetches are directed to external memory.
On the AT89S52, if EA is connected to VCC, program fetches to addresses 0000H through
1FFFH are directed to internal memory and fetches to addresses 2000H through FFFFH
are to external memory.
Data Memory
The AT89S52 implements 256 bytes of on-chip RAM. The upper 128 bytes occupy a
parallel address space to the Special Function Registers. This means that the upper 128
bytes have the same addresses as the SFR space but are physically separate from SFR
space.
When an instruction accesses an internal location above address 7FH, the address mode
used in the instruction specifies whether the CPU accesses the upper 128 bytes of RAM
or the SFR space. Instructions which use direct addressing access of the SFR space.
P a g e | 53
For example, the following direct addressing instruction accesses the SFR at location
0A0H (which is P2).
MOV 0A0H, #data
Instructions that use indirect addressing access the upper 128 bytes of RAM. For
example, the following indirect addressing instruction, where R0 contains 0A0H,
accesses the data byte at address 0A0H, rather than P2 (whose address is 0A0H).
MOV @R0, #data
Note that stack operations are examples of indirect addressing, so the upper 128 bytes
of data RAM are available as stack space.
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5.2 MICROCONTROLLER PROGRAM
ORG 0000H
SET B P1.0
SETB P1.0
CLR P2.0
MOV R3,#00H
MOV P3,R3
CHECK: JNB P1.1,LOW 1
MOV R1,#01H
LJMP NEXT1
LOW1: MOV R1,#00
NEXT1: JNB P1.0,LOW2
MOV R2,#01H
JMP NEXT 2
LOW2: MOV R2#00H
NEXT2: MOV A,R1
XRL A,R2
CJNE A,#01 ,RESET
ENTER: CJNE R1,# 01H,EXIT
CHECKEN: JNB P1.0,LOW3
MOV R2,#01H
P a g e | 55
LJMP NEXT3
LOW3: MOV R2,#00H
NEXT3: CJNE R2,#01H,CHECKEN
LJMP ENTERPG
CHECKENAG: JNB P1.0,LOW4
MOV R2,#01H
LJMP NEXT 4
LOW4: MOVR2,#00H
NEXT4: CJNE R2,#00H,CHECKEN AG
LJMP RESET
EXIT: CJNE R2,#01,ENTER
CHECKEX: JNB P1.1,LOW5
MOVR1,#01
LJMP NEXT5
LOW5: MOV R1 #00H
NEXT5: CJNE R1,#01H,CHECKEX
LJMP EXITPG
CHECKENXAG: JNB P1.1 LOW6
MOV R1,#01
LJMP NEXT6
LOW6: MOV R1,#00H
NEXT6: CJNE R1,#00H,CHECKENEX AG
P a g e | 56
LJMP RESET
RESET: MOV R1,#00H
MOV R2,#00H
LJMP CHECK
ENTER PG: INC R3
MOV A,R3
MOV P3,A
SET B P2.0
LJMP CHECKENAG
EXITPG: DEC R3
MOV A,R3
MOV P3,A
CJNE R3,#00H,CHECKEXAG
CLR P2.0
LJMP CHECKENEXAG
END
P a g e | 57
5.3 FLOW CHART
NO NO
YES YES
NO NO
YES YES
NO
Start
Visitor counter
C=0
DISPLAY
Is IR
Receive 2
detects
Is IR
Receiver1
detects
Wait tn time Wait tn time
Is IR
Receiver2
detects
Is IR
Receiver1
detects
Decrement
C = C -- 1
Increment
C = C + 1 DISPLAY
Is
C=0
RELAY OFF RELAY ON
Lights
Switched OFF
Lights
Switched ON
P a g e | 58
6. Software Development
Microcontroller Model Functionality- The core of any embedded system design is the
microcontroller and the completeness of the model as well as its accuracy are therefore
of primary importance. That simulation models for
Microcontrollers not only support a peripheral that want to use but support the mode
which want to use the peripheral and to a satisfactory level of detail. Some
microcontroller models are in fact little more than instruction set simulators (which is
light years away from the level of detail in Proteus VSM microcontroller models) The
following chart details model particulars Peripheral Support-
In embedded systems design it's vital that have simulation models for the peripherals
likely to use. Aside from the standard collection of TTL/CMOS libraries, op amps, diodes,
transistors, etc. the following chart lists some common embedded peripherals and their
support within various packages.
PIC C Compiler-
This integrated C development environment gives developers the capability to quickly
produce very efficient code from an easily maintainable high level language.
The compiler includes built-in functions to access the PIC microcontroller hardware such
as READ_ADC to read a value from the A/D converter. Discrete I/O is handled by
describing
the port characteristics in a PRAGMA. Functions such as INPUT and OUTPUT_HIGH will
properly maintain the tri-state registers. Variables including structures may be directly
mapped
to memory such as I/O ports to best represent the hardware structure in C.
P a g e | 59
7. Seven Segment Display
A seven-segment display (SSD), or seven-segment indicator, is a form of electronic
display device for displaying decimal numerals that is an alternative to the more
complex dot-matrix displays. Seven-segment displays are widely used in digital clocks,
electronic meters, and other electronic devices for displaying numerical information.
The idea of the seven-segment display is quite old. In 1910, for example, a seven-
segment display illuminated by incandescent bulbs was used on a power-plant boiler
room signal panel.
A seven segment display, as its name indicates, is composed of seven elements.
Individually on or off, they can be combined to produce simplified representations of
the arabic numerals. Often the seven segments are arranged in an oblique (slanted)
arrangement, which aids readability. In most applications, the seven segments are of
nearly uniform shape and size (usually elongated hexagons, though trapezoids and
rectangles can also be used), though in the case of adding machines, the vertical
segments are longer and more oddly shaped at the ends in an effort to further enhance
readability.
Each of the numbers 0, 6, 7 and 9 may be represented by two or more different glyphs
on seven-segment displays.
The seven segments are arranged as a rectangle of two vertical segments on each side
with one horizontal segment on the top, middle, and bottom. Additionally, the seventh
segment bisects the rectangle horizontally. There are also fourteen-segment displays
and sixteen-segment displays (for full alphanumerics); however, these have mostly been
replaced by dot-matrix displays.
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PARTS AND MATERIALS
• 4511 BCD-to-7seg latch/decoder/driver (Radio Shack catalog # 900-4437)
• Common-cathode 7-segment LED display (Radio Shack catalog # 276-075)
• Eight-position DIP switch (Radio Shack catalog # 275-1301)
• Four 10 kΩ resistors
• Seven 470 Ω resistors
• One 6 volt battery
Caution! The 4511 IC is CMOS, and therefore sensitive to static electricity
P a g e | 61
There are two important types of 7-segment LED display. In a common cathodedisplay,
the cathodes of all the LEDs are joined together and the individual segments are
illuminated by HIGH voltages. In a common anode display, the anodes of all the LEDs are
joined together and the individual segments are illuminated by connecting to a LOW
voltage.
The 4511 is designed to drive a common cathode display and won't work with a
common anode display. You need to check that you are using the right kind of display
before you start building.
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The 0.56 in. 7-segment display common cathode available from Rapid works well as part
of a prototype board circuit.
P a g e | 63
FEATURES
* 0.52 inch (13.2 mm) DIGIT HEIGHT.
* CONTINUOUS UNIFORM SEGMENTS.
* LOW POWER REQUIREMENT.
* EXCELLENT CHARACTERS APPEARANCE.
* HIGH BRIGHTNESS + HIGH CONTRAST.
* WIDE VIEWING ANGLE.
* SOLID STATE RELIABILITY.
* CATEGORIZED FOR LUMINOUS INTENSITY.
DESCRIPTION
The LTS-547AP is a 0.52 inch (13.2 mm) digit height single digit
seven-segment display. This device utilizes bright red LED chips,
which are made from GaP on a transparent GaP substrate, and has
a gray face and white segments.
DEVICE
PART NO DESCRIPTION
BRIGHT RED COMMON CATHODE
LTS-547AP RT.HAND DECIMAL
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INTERNAL CIRCUIT DIAGRAM
PIN CONNECTION
No. CONNECTION
1 ANODE E
2 ANODE D
3 COMMON CATHODE
4 ANODE C
5 ANODE DP
6 ANODE B
7 ANODE A
8 COMMON CATHODE
9 ANODE F
10 ANODE G
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ABSOLUTE MAXIMUM RATING AT Ta=25°C
PARAMETER MAXIMUM RATING UNIT
Power Dissipation Per Segment 40 mW
Peak Forward Current Per Segment (
1/10 Duty Cycle, 0.1ms Pulse Width )
60 mA
Continuous Forward Current Per
Segment Derating Linear From 25C
Per Segment
15
0.2
MA
MA/C
Reverse Voltage Per Segment 5 V
Operating Temperature Range -35°C to +85°C
Storage Temperature Range -35°C to +85C
Solder Temperature: max 260C for max 3sec at 1.6mm below seating
plane.
ELECTRICAL / OPTICAL CHARACTERISTICS AT Ta=25°C
PARAMETER SYMBOL MIN
.
TYP. MAX
.
UNIT TEST CONDITION
Average Luminous Intensity Iv 320 800 |icd IF=10mA
Peak Emission Wavelength Xp 697 nm IF=20mA
Spectral Line Half-Width Ak 90 nm IF=20mA
Dominant Wavelength 657 nm IF=20mA
Forward Voltage Per
Segment
VF 2.1 2.6 V IF=20mA
Reverse Current Per Segment IR 100 |lA VR=5V
Luminous Intensity Matching
Ratio
Iv-m 2:1 IF=10mA
Note: Luminous intensity is measured with a light sensor and filter combination that approximates the CIE
(Commision Internationale De L'Eclairage) eye-response curve.
P a g e | 66
TYPICAL ELECTRICAL / OPTICAL CHARACTERISTIC CURVES
P a g e | 67
8.RELAY
A relay is an electrically operated switch used to isolate one electrical circuit from
another. In its simplest form, a relay consists of a coil used as an electromagnet to open
and close switch contacts. Since the two circuits are isolated from one another, a lower
voltage circuit can be used to trip a relay, which will control a separate circuit that
requires a higher voltage or amperage. Relays can be found in early telephone exchange
equipment, in industrial control circuits, in car audio systems, in automobiles, on water
pumps, in high-power audio amplifiers and as protection devices.
Relay Switch Contacts
The switch contacts on a relay can be "normally open" (NO) or "normally closed" (NC)--
that is, when the coil is at rest and not energized (no current flowing through it), the
switch contacts are given the designation of being NO or NC. In an open circuit, no
current flows, such as a wall light switch in your home in a position that the light is off.
In a closed circuit, metal switch contacts touch each other to complete a circuit, and
current flows, similar to turning a light switch to the "on" position. In the accompanying
schematic diagram, points A and B connect to the coil. Points C and D connect to the
switch. When you apply a voltage across the coil at points A and B, you create an
electromagnetic field, which attracts a lever in the switch, causing it to make or break
contact in the circuit at points C and D (depending if the design is NO or NC). The switch
contacts remain in this state until you remove the voltage to the coil. Relays come in
P a g e | 68
different switch configurations. The switches may have more than one "pole," or switch
contact. The diagram shows a "single pole single throw" configuration, referred to as
SPST. This is similar to a wall light switch in your home. With a single "throw" of the
switch, you close the circuit.
A simple electromagnetic relay consists of a coil of wire wrapped around a soft iron
core, an iron yoke which provides a low reluctance path for magnetic flux, a movable
iron armature, and one or more sets of contacts (there are two in the relay pictured).
The armature is hinged to the yoke and mechanically linked to one or more sets of
moving contacts. It is held in place by a spring so that when the relay is de-energized
there is an air gap in the magnetic circuit. In this condition, one of the two sets of
contacts in the relay pictured is closed, and the other set is open. Other relays may have
more or fewer sets of contacts depending on their function. The relay in the picture also
has a wire connecting the armature to the yoke. This ensures continuity of the circuit
between the moving contacts on the armature, and the circuit track on the printed
circuit board (PCB) via the yoke, which is soldered to the PCB.
When an electric current is passed through the coil it generates a magnetic field that
activates the armature, and the consequent movement of the movable contact(s) either
makes or breaks (depending upon construction) a connection with a fixed contact. If the
set of contacts was closed when the relay was de-energized, then the movement opens
the contacts and breaks the connection, and vice versa if the contacts were open. When
the current to the coil is switched off, the armature is returned by a force,
approximately half as strong as the magnetic force, to its relaxed position. Usually this
force is provided by a spring, but gravity is also used commonly in industrial motor
starters. Most relays are manufactured to operate quickly. In a low-voltage application
this reduces noise; in a high voltage or current application it reduces arcing.
When the coil is energized with direct current, a diode is often placed across the coil to
dissipate the energy from the collapsing magnetic field at deactivation, which would
otherwise generate a voltage spike dangerous to semiconductor circuit components.
Some automotive relays include a diode inside the relay case. Alternatively, a contact
protection network consisting of a capacitor and resistor in series (snubber circuit) may
absorb the surge. If the coil is designed to be energized with alternating current (AC), a
P a g e | 69
small copper "shading ring" can be crimped to the end of the solenoid, creating a small
out-of-phase current which increases the minimum pull on the armature during the AC
cycle.
A solid-state relay uses a thyristor or other solid-state switching device, activated by the
control signal, to switch the controlled load, instead of a solenoid. An optocoupler (a
light-emitting diode (LED) coupled with a photo transistor) can be used to isolate control
and controlled circuits.
Latching relay
Latching relay with permanent magnet
A latching relay has two relaxed states (bistable). These are also called "impulse",
"keep", or "stay" relays. When the current is switched off, the relay remains in its last
state. This is achieved with a solenoid operating a ratchet and cam mechanism, or by
having two opposing coils with an over-center spring or permanent magnet to hold the
armature and contacts in position while the coil is relaxed, or with a remanent core. In
the ratchet and cam example, the first pulse to the coil turns the relay on and the
second pulse turns it off. In the two coil example, a pulse to one coil turns the relay on
and a pulse to the opposite coil turns the relay off. This type of relay has the advantage
that one coil consumes power only for an instant, while it is being switched, and the
relay contacts retain this setting across a power outage. A remanent core latching relay
requires a current pulse of opposite polarity to make it change state.
P a g e | 70
Reed relay
A reed relay is a reed switch enclosed in a solenoid. The switch has a set of contacts
inside an evacuated or inert gas-filled glass tube which protects the contacts against
atmospheric corrosion; the contacts are made of magnetic material that makes them
move under the influence of the field of the enclosing solenoid. Reed relays can switch
faster than larger relays, require only little power from the control circuit, but have low
switching current and voltage ratings. In addition, the reeds can become magnetized
over time, which makes them stick 'on' even when no current is present; changing the
orientation of the reeds with respect to the solenoid's magnetic field will fix the
problem.
Mercury-wetted relay
A mercury-wetted reed relay is a form of reed relay in which the contacts are wetted
with mercury. Such relays are used to switch low-voltage signals (one volt or less) where
the mercury reduces the contact resistance and associated voltage drop, for low-current
signals where surface contamination may make for a poor contact, or for high-speed
applications where the mercury eliminates contact bounce. Mercury wetted relays are
position-sensitive and must be mounted vertically to work properly. Because of the
toxicity and expense of liquid mercury, these relays are now rarely used. See also
mercury switch.
Polarized relay
A polarized relay placed the armature between the poles of a permanent magnet to
increase sensitivity. Polarized relays were used in middle 20th Century telephone
exchanges to detect faint pulses and correct telegraphic distortion. The poles were on
P a g e | 71
screws, so a technician could first adjust them for maximum sensitivity and then apply a
bias spring to set the critical current that would operate the relay.
Machine tool relay
A machine tool relay is a type standardized for industrial control of machine tools,
transfer machines, and other sequential control. They are characterized by a large
number of contacts (sometimes extendable in the field) which are easily converted from
normally-open to normally-closed status, easily replaceable coils, and a form factor that
allows compactly installing many relays in a control panel. Although such relays once
were the backbone of automation in such industries as automobile assembly, the
programmable logic controller (PLC) mostly displaced the machine tool relay from
sequential control applications.
A relay allows circuits to be switched by electrical equipment: for example, a timer
circuit with a relay could switch power at a preset time. For many years relays were the
standard method of controlling industrial electronic systems. A number of relays could
be used together to carry out complex functions (relay logic). The principle of relay logic
is based on relays which energize and de-energize associated contacts. Relay logic is the
predecessor of ladder logic, which is commonly used in Programmable logic controllers.
Ratchet relay
This is again a clapper type relay which does not need continuous current through its
coil to retain its operation.
Contactor relay
A contactor is a very heavy-duty relay used for switching electric motors and lighting
loads, although contactors are not generally called relays. Continuous current ratings for
common contactors range from 10 amps to several hundred amps. High-current
contacts are made with alloys containing silver. The unavoidable arcing causes the
contacts to oxidize; however, silver oxide is still a good conductor. Such devices are
often used for motor starters. A motor starter is a contactor with overload protection
P a g e | 72
devices attached. The overload sensing devices are a form of heat operated relay where
a coil heats a bi-metal strip, or where a solder pot melts, releasing a spring to operate
auxiliary contacts. These auxiliary contacts are in series with the coil. If the overload
senses excess current in the load, the coil is de-energized. Contactor relays can be
extremely loud to operate, making them unfit for use where noise is a chief concern.
Solid-state relay
Solid state relay with no moving parts
A solid state relay (SSR) is a solid state electronic component that provides a similar
function to an electromechanical relay but does not have any moving components,
increasing long-term reliability. Every solid-state device has a small voltage drop across
it. This voltage drop limited the amount of current a given SSR could handle. The
minimum voltage drop for such a relay is a function of the material used to make the
device. Solid-state relays rated to handle 100 to 1,200 Amperes, have become
commercially available. Compared to electromagnetic relays, they may be falsely
triggered by transients.
P a g e | 73
Solid state contactor relay
25 A or 40 A solid state contactors
A solid state contactor is a heavy-duty solid state relay, including the necessary heat
sink, used for switching electric heaters, small electric motorsand lighting loads; where
frequent on/off cycles are required. There are no moving parts to wear out and there is
no contact bounce due to vibration. They are activated by AC control signals or DC
control signals from Programmable logic controller (PLCs), PCs, Transistor-transistor
logic (TTL) sources, or other microprocessor and microcontroller controls.
Buchholz relay
A Buchholz relay is a safety device sensing the accumulation of gas in large oil-filled
transformers, which will alarm on slow accumulation of gas or shut down the
transformer if gas is produced rapidly in the transformer oil.
Forced-guided contacts relay
A forced-guided contacts relay has relay contacts that are mechanically linked together,
so that when the relay coil is energized or de-energized, all of the linked contacts move
together. If one set of contacts in the relay becomes immobilized, no other contact of
the same relay will be able to move. The function of forced-guided contacts is to enable
P a g e | 74
the safety circuit to check the status of the relay. Forced-guided contacts are also known
as "positive-guided contacts", "captive contacts", "locked contacts", or "safety relays".
Overload protection relay
Electric motors need overcurrent protection to prevent damage from over-loading the
motor, or to protect against short circuits in connecting cables or internal faults in the
motor windings.[3] One type of electric motor overload protection relay is operated by a
heating element in series with the electric motor. The heat generated by the motor
current heats a bimetallic strip or melts solder, releasing a spring to operate contacts.
Where the overload relay is exposed to the same environment as the motor, a useful
though crude compensation for motor ambient temperature is provided.
The Single Pole Double Throw Relay
A single pole double throw (SPDT) relay configuration switches one common pole to two
other poles, flipping between them. As shown in the schematic diagram, the common
point E completes a circuit with C when the relay coil is at rest, that is, no voltage is
applied to it. This circuit is "closed." A gap between the contacts of point E and D creates
an "open" circuit. When you apply power to the coil, a metal level is pulled down,
closing the circuit between points E and D and opening the circuit between E and C. A
single pole double throw relay can be used to alternate which circuit a voltage or signal
will be sent to.
How Relay Works In This Circuit :-
A single pole dabble throw (SPDT) relay is connected to port RB1 of the microcontroller
through a driver transistor. The relay requires 12 volts at a current of around 100ma,
which cannot provide by the microcontroller. So the driver transistor is added. The relay
is used to operate the external solenoid forming part of a locking device or for operating
any other electrical devices. Normally the relay remains off. As soon as pin of the
microcontroller goes high, the relay operates. When the relay operates and releases.
Diode D2 is the standard diode on a mechanical relay to prevent back EMF from
damaging Q3 when the relay releases. LED L2 indicates relay on.
P a g e | 75
8.PROJECT PICTURES
Variable Power Supply Unit
Display Unit Relay Unit
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Processor Unit
Receiver Units
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Variable Power Supply Unit
Transmitter Units
P a g e | 78
9.CONCLUSION
Testing And Results
We started our project by making power supply. That is easy for me but when we turn
toward the main circuit, there are many problems and issues related to it, which we
faced, like component selection, which components is better than other and its feature
and cost wise a, then refer the data books and other materials related to its.
We had issues with better or correct result, which we desired. And also the software
problem.
We also had some soldering issues which were resolved using continuity checks
performed on the hardware.
We had issues with better or correct result, which we desired. And also the software
problem.
We also had some soldering issues which were resolved using continuity checks
performed on the hardware.
We started testing the circuit from the power supply. There we got over first trouble.
After getting 9V from the transformer it was not converted to 5V and the circuit
received 9V.
As the solder was shorted IC 7805 got burnt. So we replaced the IC7805.also the circuit
part around the IC7805 were completely damaged..with the help of the solder we made
the necessary paths.
P a g e | 79
DIFFICULTIES AND RECTIFICATION:
The common difficulties faced while making this project were:
1 . L a c k o f u n i f o r m i t y f o r t h e “ C o m m o n G r o u n d ” : The Relay circuit, the
Seven Segment circuit, the I.R sensors, and the Microcontroller kit, all have to be
connected to the “common ground”.There was a mismatch between the values of
ground given to each and wasn’t constant for all. The mistake was observed and
corrected.
2. Erroneously giving “Human Ground” to the circuit: In the Relay circuit, the
triggering sound was observed when connections were made, i.e. one terminal to
ground and other to the 5V of micro controller. Even after the connections were
removed, triggering sound was observed. After much thinking and speculation it was
observed that, supplying Human Ground was causing the triggering
3. Giving a D.C (12V) supply to 5 relays simultaneously: Instead of using a
battery or an adapter, we created a Power Source using a Step-down Transformer,
Bridge Rectifier, Capacitor Filter and Voltage Regulator. That’s how we got a 12volt D.C
supply from the domestic 220 volts A.C.
4 . I m p r o p e r S o l d e r i n g : Due to flow improper soldering, the 3 legs of the
voltage regulator were short circuited, (as concluded by the use of a millimeter).It was
de-soldered and placed again with legs open wider than before.
5 . I m p r o p e r p l a c e m e n t o f t h e b u l b s : In order to exactly simulate the model,
we had put bulbs on the ceiling of the wooden structure. Once all of them were
placed together, it was difficult to understand which bulb was illuminated when. We
then took a corrective measure and decided to place the bulbs on the roofs, and it could
be clearly seen that which bulb is being lit and where.
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APPLICATIONS AND FUTURE PROSPECTS
General applications
This project, Automatic light control in a room with person counter, can be used in
areas, like:
1 . P o w e r c o n s e r v a t i o n a n d i t s e f f i c i e n t u s e : The genius of this idea is
the efficient use of power. One of the most crucial issues in today’s times is energy
conservation. In spite of repeated reminders about “switching off the lights and fans
when you leave” it’s hardly done with any effect. The usage of an Automatic Room Light
Controller and Visitor Counter ensures both, Optimum usage and Minimum wastage. A
recent survey by “The NTPC” has shown that, if for an average consumer of electricity,
the appliances are switched off as use; there is a saving of more than 36% of power.
P a g e | 81
Thus having an automatic control of the appliances is like banking and storing that
electricity for future use. After all, power saved is power generated.
Specific Applications of the Visitor Counter and Display:
1 . P r e v e n t i n g t h e f t i n a c o m m e r c i a l c o m p l e x :
If a showroom of a multiplex shopping Centre has an Automatic Room Light
Controller and Visitor Counter installed on every entrance and exit point, the “Visitor
Counter” feature comes into play.
2 . D i s t r i b u t i o n o f t h e e x a c t n u m b e r o f a r t i c l e s :
Exact information of number of people present facilitates proper distribution of articles
be it books, reports or refreshments to the people.
In large capacity arenas, such as auditoriums, or conference halls, it’s difficult to
know the number of people presents accurately. Now, while conducting workshops,
presentations or lectures, there is often distribution of expensive articles like books or
confidential ones like reports and worksheets. Knowing the exact number required is
crucial. It ensures that each one gets one and only one preventing wastage as well as
deficiency.
3 . C r o s s v e r i f i c a t i o n o f a t t e n d a n c e :
Knowledge of the exact number of people present for a lecture or workshop, as
indicated by the visitor counter, in any educational institute eliminates any scope of a
false attendance or “proxy”. With as little effort as glancing at no of people present as
per the display it ensures vigilance and discipline in the classroom. Other than that, in
Cinema Halls and other events where entry is strictly as per passes or invitations, like
concerts and fests the number of people entered and the tickets or passes gathered can
be cross checked.
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FUTURE EXPANSION
By using this circuit and proper power supply we can implement various applications
Such as fans, tube lights, etc.
By modifying this circuit and using two relays we can achieve a task of opening and
closing the door.
APPLICATION, ADVANTAGES & DISADVANTAGES
Application:-
For counting purposes
For automatic room light control
Advantages:-
Low cost
Easy to use
Implement in single door
Disadvantages:-
It is used only when one single person cuts the rays of the sensor hence it cannot be
used when two person cross simultaneously.
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11.APPENDIX
Overview of IC 89S752
Programmable Clock Out A 50% duty cycle clock can be programmed to come out on P1.0, as shown in Figure 9. This pin, besides being a regular I/O
pin, has two alternate functions. It can be programmed to input the external clock for Timer/Counter 2 or to output a 50%
duty cycle clock ranging from 61 Hz to 4 MHz at a 16 MHz operating frequency.
To configure the Timer/Counter 2 as a clock generator, bit C/T2 (T2CON.1) must be cleared and bit T2OE (T2MOD.1) must
be set. Bit TR2 (T2CON.2) starts and stops the timer.
The clock-out frequency depends on the oscillator frequency and the reload value of Timer 2 capture registers (RCAP2H,
RCAP2L), as shown in the following equation.
Clock-Out Frequency
In the clock-out mode, Timer 2 roll-overs will not generate an interrupt. This behavior is similar to when Timer 2 is used as a
baud-rate generator. It is possible to use Timer 2 as a baud-rate generator and a clock generator simultaneously. Note,
however, that the baud-rate and clock-out frequencies cannot be determined independently from one another since they both
use RCAP2H and RCAP2L.
Interrupts The AT89S52 has a total of six interrupt vectors: two external interrupts (INTO and INT1), three timer interrupts (Timers 0,
1, and 2), and the serial port interrupt. These interrupts are all shown in Figure 10.
Each of these interrupt sources can be individually enabled or disabled by setting or clearing a bit in Special Function
Register IE. IE also contains a global disable bit, EA, which disables all interrupts at once.
Note that Table 5 shows that bit position IE.6 is unimple-mented. In the AT89S52, bit position IE.5 is also unimple-mented.
User software should not write 1s to these bit positions, since they may be used in future AT89 products.
Timer 2 interrupt is generated by the logical OR of bits TF2 and EXF2 in register T2CON. Neither of these flags is cleared
by hardware when the service routine is vectored to. In fact, the service routine may have to determine whether it was TF2 or
EXF2 that generated the interrupt, and that bit will have to be cleared in software.
The Timer 0 and Timer 1 flags, TF0 and TF1, are set at S5P2 of the cycle in which the timers overflow. The values are then
polled by the circuitry in the next cycle. However, the Timer 2 flag, TF2, is set at S2P2 and is polled in the same cycle in
which the timer overflows.
Oscillator Frequency
4x[65536(RCAP2H,RCAP2L)]
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Table. Interrupt Enable (IE) Register
(MSB) (LSB)
EA - ET2 ES ET1 EX1 ETO EXO
Enable
Bit
= 1 enables the interrupt.
Enable
Bit
= O disables the interrupt.
Symbol
Position
Function
EA IE.7 Disables all interrupts. If EA = O, no interrupt is acknowledged. If EA = 1, each interrupt source is individually enabled or disabled by setting or clearing its enable bit.
- IE.6 Reserved.
ET2 IE.5 Timer 2 interrupt enable bit.
ES IE.4 Serial Port interrupt enable bit.
ET1 IE.3 Timer 1 interrupt enable bit.
EX1 IE.2 External interrupt 1 enable bit.
ETO IE.1 Timer O interrupt enable bit.
EXO IE.O External interrupt O enable bit.
User software should never write 1s to unimplemented bits, because they may be used in future AT89 products.
Figure. Interrupt Sources
IEO
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Oscillator Characteristics XTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier that can be configured for use as an on-
chip oscillator, as shown in Figure 11. Either a quartz crystal or ceramic resonator may be used. To drive the device from an
external clock source, XTAL2 should be left unconnected while XTAL1 is driven, as shown in Figure 12. There are no
requirements on the duty cycle of the external clock signal, since the input to the internal clocking circuitry is through a
divide-by-two flip-flop, but minimum and maximum voltage high and low time specifications must be observed.
Idle Mode In idle mode, the CPU puts itself to sleep while all the on-chip peripherals remain active. The mode is invoked by software.
The content of the on-chip RAM and all the special functions registers remain unchanged during this mode. The idle mode
can be terminated by any enabled interrupt or by a hardware reset.
Note that when idle mode is terminated by a hardware reset, the device normally resumes program execution from where it
left off, up to two machine cycles before the internal reset algorithm takes control. On-chip hardware inhibits access to
internal RAM in this event, but access to the port pins is not inhibited. To eliminate the possibility of an unexpected write to
a port pin when idle mode is terminated by a reset, the instruction following the one that invokes idle mode should not write
to a port pin or to external memory.
Power-down Mode In the Power-down mode, the oscillator is stopped, and the instruction that invokes Power-down is the last instruction
executed. The on-chip RAM and Special Function Registers retain their values until the Power-down mode is terminated.
Exit from Power-down mode can be initiated either by a hardware reset or by an enabled external interrupt.
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10.BIBLOGRAPHY
Microprocessor Architecture, Programming & Application-R. Gaonkar, Wiley
Advance Microprocessor -Badriram & Badriram-MH
www.wikipedia.org
www.datasheetcatalog.com
www.electronicsforyou.com
www.projectworld.com
www.alldatasheets.com