TITLEA Mini Project report submitted in partial fulfillment of
the requirements
For the Award of Degree of BACHELOR OF TECHNOLOGY
In
ELECTRONICS AND COMMUNICATIONS ENGINEERING
By
Bhagyashri Bhosle (11N81A04D7)
D Ramakrishna Reddy (11N81A04F0)
Shaik Zakeer (11N81A04G8)
Under the Esteemed guidance of
Mr. S Harish Kumar (Asst. Professor ECE Dept.)
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING
SPHOORTHY ENGINEERING COLLEGE(Affiliated to J.N.T. University,
Hyderabad)
Nadargul (Vill), Sagar Ring Road, Near Vanasthalipuram,
Saroornagar,
Hyderabad
2013-2014DEPARTMENT OF ELECTRONICS AND
COMMUNICATIONENGINEERING
SPHOORTHY ENGINEERING COLLEGE (SEC)
Nadargul (Vill), Sagar Road, Near Vanasthalipuram,
Saroornagar
HYDERABAD
CERTIFICATE
This is to certify that the mini project entitled
MICROCONTROLLER BASED AUTOMATIC ROOM LIGHT CONTROL WITH VISITOR
COUNTER FOR AUDITORIUM is a bonafide work carried out by Bhagyashri
Bhosle (11N81A04D7), D Ramakrishna Reddy (11N81A04F0), Shaik Zakeer
(11N81A04G8), in partial fulfillment for the award of Degree of
BACHELOR OF TECHNOLOGY IN ELECTRONICS AND COMMUNICATION ENGINEERING
of Jawaharlal Nehru Technological University, Hyderabad during the
year 2013-2014.Name: S. Harish Kumar
P PRAVEEN RAJUINTERNAL GUIDE HEAD OF THE DEPARTMENT
Prof. Dr. V. CHANDRA MOULIExternal Examiner PRINCIPAL
SPHOORTHY ENGINEERING COLLEGE
(Affiliated to J.N.T. University, Hyderabad)
Nadargul (Vill), Sagar Road, Near Vanasthalipuram,
Saroornagar.
HYDERABAD - 501510.
________________________________________________________________________
DECLARATION
We, Bhagyashri Bhosle (11N81A04D7), D.Ramakrishna
Reddy(11N81A04F0), Shaik Zakeer (11N81A04G8) hereby declare that
the work embodied in this mini project dissertation entitled
MICROCONTROLLER BASED AUTOMATIC ROOM LIGHT CONTROL WITH VISITOR
COUNTER FOR AUDITORIUM submitted to the Sphoorthy Engineering
College Affiliated to JNTU, Hyderabad, for partial fulfillment of
the degree of B.Tech in Electronics And Communications Engineering
has been carried out by us under the supervision of INTERNAL GUIDE
S.HARISH KUMAR , ASST PROFESSOR, ECE DEPT., Sphoorthy Engineering
College, Hyderabad. To the best of my knowledge, this work has not
been submitted for any other degree in any University.
Bhagyashri Bhosle (11N81A04D7) D.Ramakrishna Reddy (11N81A04F0)
Shaik Zakeer (11N81A04G8) ACKNOWLEDGEMENTThe completion of this
mini-project work gives me an opportunity to convey my gratitude to
all those who have helped me to reach a stage where I have the
confidence to launch my career in the competitive world in the
field of ECE.
I express my sincere thanks to Prof. Dr. V. CHANDRA MOULI,
Principal, Sphoorthy Engineering College for providing all
necessary facilities in completing my mini project report.
I express my sense of gratitude to P PRAVEEN RAJU, Head of
Department of ELECTRONICS AND COMMUNICATION ENGINEERING, who
encouraged me to select the project and completion of this
mini-project with providing necessary facilities.
My honest thankfulness to S HARISH KUMAR , Asst Professor, ECE
dept.,(Internal Guide) for his kind help and for giving me the
necessary guidance and valuable suggestions in completing this
mini-project work and in preparing this report
I take the opportunity to express my gratitude to the
Management, Teaching and Non-teaching Staff of Sphoorthy
Engineering College for their kind co-operation during the period
of my Study.
Finally, I would like to thank my parents & friends for
their continuous encouragement and support during the entire course
of this mini-project work.
Bhagyashri Bhosle (11N81A04D7) D.Ramakrishna Reddy (11N81A04F0)
Shaik Zakeer (11N81A04G8)
CONTENTS NAME
PAGE NO.1. ABSTRACT2. TECHNICAL SPECIFICATION
3. LIST OF FIGURES
74. LIST OF TABLES
75. BLOCK DIAGRAM OF 89S52
86. BLOCK DIAGRAM OF POWER SUPPLY
8CHAPTER1: INTRODUCTION
9CHAPTER2: POWER SUPPLY
10
2.1 Transformer
10 2.2 Rectifier
11 2.3 Filter
11 2.4 Voltage Regulator
11CHAPTER 3: MICRO CONTROLLER
12 3.1 Features of AT89S52
13 3.2 Description
13 3.3 Pin Diagram
14
3.4 Pin Description
14
3.5 Machine Cycle for 8051
17CHAPTER 4: SOFTWARE COMPONENTS
18 4.1 Keil Compiler
4.2 ProloadCHAPTER 5: IR SECTION
19 5.1 What are Infrared
19 5.2 IR in Electronics
19
5.3 IR Generator
20 5.4 Rc-5
22 5.5 IR Receiver
23 5.5.1 Description 5.5.2 Features 5.5.3 Suitable Data
FormatCHAPTER 6: L293D SREPPER MOTOR DRIVER
26CHAPER 7: STEPPER MOTOR
28 7.1 Advantages
29 7.2 Disadvantages
30 7.3 Open Loop Operation
30 7.4 Stepper Motor Types
30 7.5 Variable Reluctance (Vr)
30 7.6 Permanent Magnet
31 7.7 Hybrid (Hb)
32 7.8 When to Use Stepper Motor
32 7.9 Rotating Magnetic Field
33 7.10 Torque Generation
33 7.11 Step Angle Accuracy
34 7.12 Torque versus Speed Characteristics
35 7.13 Single Step Response and Resonance
35 7.14 Few Definitions of Stepper Motor
36 7.15 Stepper Motor Interfacing with Microcontroller37 CHAPTER
8: RELAYS
8.1 Operation
38 8.2 Driving a Relay
40 8.3 Relay Interfacing with Microcontroller
41CHAPTER 9 DISPLAY COMPONENTS 9.1 Light Dependent Resistor
41 9.2 Liquid Crystal Device
42
9.2.1 Pin Function
9.2.2 Lcd Screen
9.2.3 Lcd Basic Commands
9.2.4 Lcd Connections
9.2.5 Lcd Initialization
9.2.6 Lcd Interfacing with MicrocontrollerCHAPTER 10: SWITCH
& LED INTERFACING WITH
MICROCONTROLLER 10.1switch Interfacing
50 10.2 Lcd Interfacing
51CHAPTER 11: WORKING PROCEDURE OF PROJECT
52CONCLUSION
55RESULTS
56REFERENCES
57ABSTRACTIn this competitive world and busy schedule human
cannot spare time to perform his daily activities manually. The
most common thing that he forgets to do is switching OFF the lights
wherever they are not required. This project is a standalone
automatic room light controller with auto door opening and closing.
The main aim of the project is to control the lighting in a room
depending upon lighting that is present in the room. Use of
embedded technology makes this closed loop feedback control system
efficient and reliable. Micro controller (AT89S52) allows dynamic
and faster control. Liquid crystal display (LCD) makes the system
user-friendly. AT89S52 micro controller is the heart of the circuit
as it controls all the functions. The system comprises of two IR
Transmitter-Receiver pairs, one of which is located in front of the
door outside the room. The other pair is located inside the room.
LDR is placed outside the room and is used to identify whether it
is day or night time. Initially the light is switched off in the
room. Whenever a person tries to enter into the room, the receiver
of first IR pair identifies the person. Then the microcontroller
opens the door by rotating the stepper motor. After the person had
entered into the room completely, the door will be closed
automatically.
The light is switched off even if anyone is present inside the
room during the day time. Similarly, the light is switched off if
no one is there inside the room or if it is night times. Thus,
depending on the intensity of light and the surrounding
temperature, the required action is performed by the
microcontroller. LCD displays the number of persons present inside
the room.
This project uses regulated 5V, 500mA power supply. 7805 three
terminal voltage regulator is used for voltage regulation. Bridge
type full wave rectifier is used to rectify the ac out put of
secondary of 230/12V step down transformer.
TECHNICAL SPECIFICATIONS
Title of the project :MICROCONTROLLER BASED AUTOMATIC ROOM LIGHT
CONTROL WITH VISITOR COUNTING FOR AUDITORIUMDomain
:Embedded Systems Design
Software
:Embedded C, Keil, Proload
Microcontroller
:AT89S52Power Supply
:+5V, 500mA Regulated Power Supply
Display
:LCD
LCD
:HD44780 16-character, 2-line (16X2)
LED
:5mm
Crystal
:11.0592MHz
Sensor
:IR Sensors
LIST OF FIGURESDESCRIPTION
PAGE NO 1. BLOCK DIAGRAM OF 89S52
82. BLOCK DIAGRAM OF POWER SUPPLY
83. POWER SUPPLY
10
4. PIN DIAGRAM OF 8051
145. BLOCK DIAGRAM OF IR RECEIVER
24
6. APPLICATION CIRCUIT FOR IR receiver
247. DIP 16 PACKAGE
268. PIN CONNECTION OF ULN2003
279. STEPPER MOTOR
2810. STEPPER MOTOR OPERATION
2911. CROSS SECTION OF VARIABLE RELUCTANCE MOTOR
3112. PM STEPPER MOTOR PRINCIPLE
3213. CROSS SCETION OF HYBRID STEPPER MOTOR
3214. MAGNETIC FLUX PATH TO A 2POLE STEPPER MOTOR WITH LAG
33
BETWEEN ROTOR &STATOR
15. POSITIONAL ACCURACY OF STEPPER MOTOR
3516. TORQUE VS SPEED CHARACTERISTICS
3517. SINGLE STEP RESPONSE VS TIME
3618. CIRCUIT SYMBOL OF A RELAY
3819. RELAY OPERATION &USE OF PROTECTION DIODES
3920. PROCEDURE ON 8BIT INITIALIZATION
4821. INTERFACING SWITCH WITH MICROCONTROLLER
5022. LED INTERFACING WITH MICRO CONTROLLER
5223. SCHEMATIC DIAGRAM
54LIST OF TABLES
1. PORT3 ALTERNATE FUNCTION
172. STEPPER MOTOR STEP ANGLE
363. LIST COMMANDS WHICH LCD RECOGNISES
45BLOCK DIAGRAM BLOCK DIAGRAM OF AT89S52
Fig1: Block Diagram of Automatic room light control BLOCK
DIAGRAM OF POWER SUPPLY:
Fig2: Block Diagram Of Power Supply
CHAPTER -1Project review
1. Introduction of Project
1.1 Project Definition:
Project title is AUTOMATIC ROOM LIGHT CONTROLLER WITH
BIDIRECTIONAL VISITOR COUNTER FOR AUDITORIUM .
The objective of this project is to make a controller based
model to count number of persons visiting particular room and
accordingly light up the room. Here we can use sensor and can know
present number of persons.
In todays world, there is a continuous need for automatic
appliances with the increase in standard of living; there is a
sense of urgency for developing circuits that would ease the
complexity of life.
Also if at all one wants to know the number of people present in
room so as not to have congestion. This circuit proves to be
helpful.1.2 Project OverviewThis 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 receiver
are obstructed , this obstruction is sensed by the
Microcontroller
CHAPTER-2BLOCK DIAGRAM AND ITS DESCRIPTION
2.1 BASIC BLOCK DIAGRAM
Fig1: Block Diagram of Automatic room light control BLOCK
DIAGRAM OF POWER SUPPLY:
Fig2: Block Diagram Of Power Supply
2.2 Block Diagram DescriptionThe basic block diagram of the
bidirectional visitor counter with automatic light controller is
shown in the above figure. Mainly this block diagram consist of the
following essential blocks.
1. Power Supply
2. Entry and Exit sensor circuit
3. AT89S52 micro-controller
4. Relay driver circuit
1. Power Supply:-
Here we used +12V and +5V dc power supply. The main function of
this block is to provide the required amount of voltage to
essential circuits. +12 voltage is given. +12V is given to relay
driver. To get the +5V dc power supply we have used here IC 7805,
which provides the +5V dc regulated power supply.
2. Enter and Exit Circuits:-
This is one of the main parts of our project. The main intention
of this block is to sense the person. For sensing the person and
light we are using the IR Sensors and light dependent register
(LDR). By using these sensors and its related circuit diagram we
can count the persons.
3. 89S52 Microcontroller:-
It is a low-power, high performance CMOS 8-bit microcontroller
with 8KB of Flash Programmable and Erasable Read Only Memory
(PEROM). The device is manufactured using Atmels high-density
nonvolatile memory technology and is compatible with the MCS-51TM
instruction set and pin out. The on-chip Flash allows the program
memory to be reprogrammed in-system or by a conventional
nonvolatile memory programmer. By combining a versatile 8-bit CPU
with Flash on a monolithic hip, the Atmel AT89S52 is a powerful
Microcontroller provides a highly flexible and cost effective
solution to many embedded control applications.
4. Relay Driver Circuit:-This block has the potential to drive
the various controlled devices. In this block mainly we are using
the transistor and the relays. One relay driver circuit we are
using to control the light. Output signal from AT89S52 is given to
the base of the transistor, which we are further energizing the
particular relay. Because of this appropriate device is selected
and it do its allotted function.
POWER SUPPLYThe input to the circuit is applied from the
regulated power supply. The a.c. input i.e., 230V from the mains
supply is step down by the transformer to 12V and is fed to a
rectifier. The output obtained from the rectifier is a pulsating
d.c voltage. So in order to get a pure d.c voltage, the output
voltage from the rectifier is fed to a filter to remove any a.c
components present even after rectification. Now, this voltage is
given to a voltage regulator to obtain a pure constant dc
voltage.
Fig3: Power Supply2.1 Transformer:Usually, DC voltages are
required to operate various electronic equipment and these voltages
are 5V, 9V or 12V. But these voltages cannot be obtained directly.
Thus the a.c input available at the mains supply i.e., 230V is to
be brought down to the required voltage level. This is done by a
transformer. Thus, a step down transformer is employed to decrease
the voltage to a required level.
2.2 Rectifier:
The output from the transformer is fed to the rectifier. It
converts A.C. into pulsating D.C. The rectifier may be a half wave
or a full wave rectifier. In this project, a bridge rectifier is
used because of its merits like good stability and full wave
rectification.
2.3 Filter:
Capacitive filter is used in this project. It removes the
ripples from the output of rectifier and smoothens the D.C. Output
received from this filter is constant until the mains voltage and
load is maintained constant. However, if either of the two is
varied, D.C. voltage received at this point changes. Therefore a
regulator is applied at the output stage.
2.4 Voltage regulator:
As the name itself implies, it regulates the input applied to
it. A voltage regulator is an electrical regulator designed to
automatically maintain a constant voltage level. In this project,
power supply of 5V and 12V are required. In order to obtain these
voltage levels, 7805 and 7812 voltage regulators are to be used.
The first number 78 represents positive supply and the numbers 05,
12 represent the required output voltage levels.
CHAPTER-3
MICROCONTROLLERS
Microprocessors and microcontrollers are widely used in embedded
systems products. Microcontroller is a programmable device. A
microcontroller has a CPU in addition to a fixed amount of RAM,
ROM, I/O ports and a timer embedded all on a single chip. The fixed
amount of on-chip ROM, RAM and number of I/O ports in
microcontrollers makes them ideal for many applications in which
cost and space are critical.
The Intel 8051 is Harvard architecture, single chip
microcontroller (C) which was developed by Intel in 1980 for use in
embedded systems. It was popular in the 1980s and early 1990s, but
today it has largely been superseded by a vast range of enhanced
devices with 8051-compatible processor cores that are manufactured
by more than 20 independent manufacturers including Atmel, Infineon
Technologies and Maxim Integrated Products.
8051 is an 8-bit processor, meaning that the CPU can work on
only 8 bits of data at a time. Data larger than 8 bits has to be
broken into 8-bit pieces to be processed by the CPU. 8051 is
available in different memory types such as UV-EPROM, Flash and
NV-RAM.
The microcontroller used in this project is AT89S52. Atmel
Corporation introduced this 89S52 microcontroller. This
microcontroller belongs to 8051 family. This microcontroller had
128 bytes of RAM, 4K bytes of on-chip ROM, two timers, one serial
port and four ports (each 8-bits wide) all on a single chip.
AT89S52 is Flash type 8051.
The present project is implemented on Keil Uvision. In order to
program the device, Proload tool has been used to burn the program
onto the microcontroller.
The features, pin description of the microcontroller and the
software tools used are discussed in the following sections.
3.1 FEATURES OF AT89S52:
8K Bytes of Re-programmable Flash Memory.
RAM is 256 bytes.
2.7V to 6V Operating Range.
Fully Static Operation: 0 Hz to 24 MHz.
Two-level Program Memory Lock.
128 x 8-bit Internal RAM.
32 Programmable I/O Lines.
Two 16-bit Timer/Counters.
Six Interrupt Sources.
Programmable Serial UART Channel.
Low-power Idle and Power-down Modes.
3.2Description:
The AT89S52 is a low-voltage, high-performance CMOS 8-bit
microcomputer with 4K bytes of Flash programmable memory. The
device is manufactured using Atmels high-density nonvolatile memory
technology and is compatible with the industry-standard MCS-51
instruction set. By combining a versatile 8-bit CPU with Flash on a
monolithic chip, the Atmel AT89S52 is a powerful microcomputer,
which provides a highly flexible and cost-effective solution to
many embedded control applications.
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 hardware reset.
3.3PIN DIAGRAM:
Fig4: Pin diagram of 80513.4PIN DESCRIPTION:
Vcc:Pin 40 provides supply voltage to the chip. The voltage
source is +5V.GND:Pin 20 is the ground.XTAL1 and XTAL2:The 8051 has
an on-chip oscillator but requires an external clock to run it.
Usually, a quartz crystal oscillator is connected to inputs XTAL1
(pin19) and XTAL2 (pin18).
There are various speeds of 8051 family. Speed refers to the
maximum oscillator frequency connected to XTAL. When the 8051 is
connected to a crystal oscillator and is powered up, the frequency
can be observed on the XTAL2 pin using the oscilloscope.
RESET:Pin9 is the reset pin. It is an input and is active high.
Upon applying a high pulse to this pin, the microcontroller will
reset and terminate all the activities. This is often referred to
as a power-on reset.
EA (External access):Pin 31 is EA. It is an active low signal.
It is an input pin and must be connected to either Vcc or GND but
it cannot be left unconnected.
The 8051 family members all come with on-chip ROM to store
programs. In such cases, the EA pin is connected to Vcc. If the
code is stored on an external ROM, the EA pin must be connected to
GND to indicate that the code is stored externally.
PSEN (Program store enable):This is an output pin.
ALE (Address latch enable):This is an output pin and is active
high.Ports 0, 1, 2 and 3:The four ports P0, P1, P2 and P3 each use
8 pins, making them 8-bit ports. All the ports upon RESET are
configured as input, since P0-P3 have value FFH on them.
Port 0(P0):Port 0 is also designated as AD0-AD7, allowing it to
be used for both address and data. ALE indicates if P0 has address
or data. When ALE=0, it provides data D0-D7, but when ALE=1, it has
address A0-A7. Therefore, ALE is used for demultiplexing address
and data with the help of an internal latch.
When there is no external memory connection, the pins of P0 must
be connected to a 10K-ohm pull-up resistor. This is due to the fact
that P0 is an open drain. With external pull-up resistors connected
to P0, it can be used as a simple I/O, just like P1 and P2. But the
ports P1, P2 and P3 do not need any pull-up resistors since they
already have pull-up resistors internally. Upon reset, ports P1, P2
and P3 are configured as input ports.
Port 1 and Port 2: With no external memory connection, both P1
and P2 are used as simple I/O. With external memory connections,
port 2 must be used along with P0 to provide the 16-bit address for
the external memory. Port 2 is designated as A8-A15 indicating its
dual function. While P0 provides the lower 8 bits via A0-A7, it is
the job of P2 to provide bits A8-A15 of the address.
Port 3:Port 3 occupies a total of 8 pins, pins 10 through 17. It
can be used as input or output. P3 does not need any pull-up
resistors, the same as port 1 and port 2. Port 3 has an additional
function of providing some extremely important signals such as
interrupts.
Table1: Port 3 Alternate Functions
3.5Machine cycle for the 8051:The CPU takes a certain number of
clock cycles to execute an instruction. In the 8051 family, these
clock cycles are referred to as machine cycles. The length of the
machine cycle depends on the frequency of the crystal oscillator.
The crystal oscillator, along with on-chip circuitry, provides the
clock source for the 8051 CPU.
The frequency can vary from 4 MHz to 30 MHz, depending upon the
chip rating and manufacturer. But the exact frequency of 11.0592
MHz crystal oscillator is used to make the 8051 based system
compatible with the serial port of the IBM PC.
In the original version of 8051, one machine cycle lasts 12
oscillator periods. Therefore, to calculate the machine cycle for
the 8051, the calculation is made as 1/12 of the crystal frequency
and its inverse is taken.CHAPTER-4
Software components
4.1KEIL COMPILER:
Keil compiler is software used where the machine language code
is written and compiled. After compilation, the machine source code
is converted into hex code which is to be dumped into the
microcontroller for further processing. Keil compiler also supports
C language code.4.2PROLOAD:
Proload is software which accepts only hex files. Once the
machine code is converted into hex code, that hex code has to be
dumped into the microcontroller and this is done by the Proload.
Proload is a programmer which itself contains a microcontroller in
it other than the one which is to be programmed. This
microcontroller has a program in it written in such a way that it
accepts the hex file from the keil compiler and dumps this hex file
into the microcontroller which is to be programmed. As the proload
programmer kit requires power supply to be operated, this power
supply is given from the power supply circuit designed above. It
should be noted that this programmer kit contains a power supply
section in the board itself but in order to switch on that power
supply, a source is required. Thus this is accomplished from the
power supply board with an output of 12volts.CHAPTER-5
IR SECTION5.1 WHAT IS INFRARED?Infrared is a energy radiation
with a frequency below our eyes sensitivity, so we cannot see
it.
Even that we can not "see" sound frequencies, we know that it
exist, we can listen them.
Even that we can not see or hear infrared, we can feel it at our
skin temperature sensors. When you approach your hand to fire or
warm element, you will "feel" the heat, but you can't see it. You
can see the fire because it emits other types of radiation, visible
to your eyes, but it also emits lots of infrared that you can only
feel in your skin.
5.2INFRARED IN ELECTRONICSInfra-Red is interesting, because it
is easily generated and doesn't suffer electromagnetic
interference, so it is nicely used to communication and control,
but it is not perfect, some other light emissions could contains
infrared as well, and that can interfere in this communication. The
sun is an example, since it emits a wide spectrum or radiation.
The adventure of using lots of infra-red in TV/VCR remote
controls and other applications, brought infra-red diodes (emitter
and receivers) at very low cost at the market.
From now on you should think as infrared as just a "red" light.
This light can means something to the receiver, the "on or off"
radiation can transmit different meanings. Lots of things can
generate infrared, anything that radiate heat do it, including out
body, lamps, stove, oven, friction your hands together, even the
hot water at the faucet.
To allow a good communication using infra-red, and avoid those
"fake" signals, it is imperative to use a "key" that can tell the
receiver what is the real data transmitted and what is fake. As an
analogy, looking eye naked to the night sky you can see hundreds of
stars, but you can spot easily a far away airplane just by its
flashing strobe light. That strobe light is the "key", the "coding"
element that alerts us.
Similar to the airplane at the night sky, our TV room may have
hundreds of tinny IR sources, our body, and the lamps around, even
the hot cup of tea. A way to avoid all those other sources, is
generating a key, like the flashing airplane. So, remote controls
use to pulsate its infrared in a certain frequency. The IR receiver
module at the TV, VCR or stereo "tunes" to this certain frequency
and ignores all other IR received. The best frequency for the job
is between 30 and 60kHz, the most used is around 36kHz5.3 IR
GENERATION
To generate a 36 kHz pulsating infrared is quite easy, more
difficult is to receive and identify this frequency. This is why
some companies produce infrared receives, that contains the
filters, decoding circuits and the output shaper, that delivers a
square wave, meaning the existence or not of the 36kHz incoming
pulsating infrared.
It means that those 3 dollars small units, have an output pin
that goes high (+5V) when there is a pulsating 36kHz infrared in
front of it, and zero volts when there is not this radiation. A
square wave of approximately 27uS (microseconds) injected at the
base of a transistor, can drive an infrared LED to transmit this
pulsating light wave. Upon its presence, the commercialreceiver
will switch its output to high level (+5V).If you can turn on and
off this frequency at the transmitter; your receiver's output will
indicate when the transmitter is on or off.Those IR demodulators
have inverted logic at its output, when a burst of IR is sensed it
drives its output to low level, meaning logic level = 1.
The TV, VCR, and Audio equipment manufacturers for long use
infra-red at their remote controls. To avoid a Philips remote
control to change channels in a Panasonic TV, they use different
codification at the infrared, even that all of them use basically
the same transmitted frequency, from 36 to 50 kHz. So, all of them
use a different combination of bits or how to code the transmitted
data to avoid interference.
5.4 RC-5:Various remote control systems are used in electronic
equipment today. The RC5 control protocol is one of the most
popular and is widely used to control numerous home appliances,
entertainment systems and some industrial applications including
utility consumption remote meter reading, contact-less apparatus
control, telemetry data transmission, and car security systems.
Philips originally invented this protocol and virtually all Philips
remotes use this protocol. Following is a description of the RC5.
When the user pushes a button on the hand-held remote, the device
is activated and sends modulated infrared light to transmit the
command. The remote separates command data into packets. Each data
packet consists of a 14-bit data word, which is repeated if the
user continues to push the remote button. The data packet structure
is as follows:
2 start bits 1 control bit 5 address bits 6 command bits.
The start bits are always logic 1 and intended to calibrate the
optical receiver automatic gain control loop. Next, is the control
bit. This bit is inverted each time the user releases the remote
button and is intended to differentiate situations when the user
continues to hold the same button or presses it again. The next 5
bits are the address bits and select the destination device. A
number of devices can use RC5 at the same time. To exclude possible
interference, each must use a different address. The 6 command bits
describe the actual command. As a result, a RC5 transmitter can
send the 2048 unique commands. The transmitter shifts the data
word, applies Manchester encoding and passes the created one-bit
sequence to a control carrier frequency signal amplitude modulator.
The amplitude modulated carrier signal is sent to the optical
transmitter, which radiates the infrared light. In RC5 systems the
carrier frequency has been set to 36 kHz. Figure below displays the
RC5 protocol.
The receiver performs the reverse function. The photo detector
converts optical transmission into electric signals, filters it and
executes amplitude demodulation. The receiver output bit stream can
be used to decode the RC5 data word. This operation is done by the
microprocessor typically, but complete hardware implementations are
present on the market as well. Single-die optical receivers are
being mass produced by a number of companies such as Siemens,
Temic, Sharp, Xiamen Hualian, Japanese Electric and others. Please
note that the receiver output is inverted (log. 1 corresponds to
illumination absence).5.5 IR RECEIVER5.5.1 Description:The
TSOP17... Series are miniaturized receivers for infrared remote
control systems. PIN diode and preamplifier are assembled on lead
frame, the epoxy package is designed as IR filter.
The demodulated output signal can directly be decoded by a
microprocessor. TSOP17.. is the standard IR remote control receiver
series, supporting all major transmission codes.
5.5.2 Features: Photo detector and preamplifier in one
package
Internal filter for PCM frequency
Improved shielding against electrical field disturbance
TTL and CMOS compatibility
Output active low
Low power consumption
High immunity against ambient light
Continuous data transmission possible (up to 2400 bps)
Suitable burst length .10 cycles/burst
Fig5: Block Diagram For IR Receiver
Fig6: Application Circuit For IR Receiver5.5.3 Suitable Data
Format
The circuit of the TSOP17 is designed in that way that
unexpected output pulses due to noise or disturbance signals are
avoided. A bandpassfilter, an integrator stage and an automatic
gain control are used to suppress such disturbances. The
distinguishing mark between data signal and disturbance signal are
carrier frequency, burst length and duty cycle. The data signal
should fulfill the following condition: Carrier frequency should be
close to center frequency of the bandpass (e.g. 38 kHz).
Burst length should be 10 cycles/burst or longer.
After each burst which is between 10 cycles and 70 cycles a gap
time of at least 14 cycles is necessary.
For each burst which is longer than 1.8ms a corresponding gap
time is necessary at some time in the data stream. This gap time
should have at least same length as the burst.
Up to 1400 short bursts per second can be received
continuously.
Some examples for suitable data format are: NEC Code, Toshiba
Micom Format, Sharp Code, RC5 Code, RC6 Code, R2000 Code, Sony
Format (SIRCS). When a disturbance signal is applied to the
TSOP17.. it can still receive the data signal. However the
sensitivity is reduced to that level that no unexpected pulses will
occur. Some examples for such disturbance signals which are
suppressed by the TSOP17 are:
DC light (e.g. from tungsten bulb or sunlight)
Continuous signal at 38 kHz or at any other frequency
Signals from fluorescent lamps with electronic ballast (an
example of the signal modulation is in the figure below).
Fig7: DIP 16 PackageCHAPTER-6
ULN2003 CURRENT DRIVERThe ULN2003 current driver is a high
voltage, high current Darlington arrays each containing seven open
collector Darlington pairs with common emitters. Each channel is
rated at 500mA and can withstand peak currents of 600mA.
Suppression diodes are included for inductive load driving and the
inputs are pinned opposite the outputs to simplify board
layout.These versatile devices are useful for driving a wide range
of loads including solenoids, relays DC motors, LED displays
filament lamps, thermal print heads and high power buffers. This
chip is supplied in 16 pin plastic DIP packages with a copper lead
frame to reduce thermal resistance.
Fig8: Pin Connection of ULN 2003This ULN2003 driver can drive
seven relays at a time. The pins 8 and 9 provide ground and Vcc
respectively. The working of ULN driver is as follows:It can accept
seven inputs at a time and produces seven corresponding outputs. If
the input to any one of the seven input pins is high, then the
value at its corresponding output pin will be low, for example if
the input at pin 6 is high, then the value at the corresponding
output i.e., output at pin 11 will be low. Similarly if the input
at a particular pin is low, then the corresponding output will be
high.CHAPTER -7
STEPPER MOTOR:
Fig9: Stepper motor
A stepper motor is a widely used device that translates
electrical pulses into mechanical movement. The stepper motor is
used for position control in applications such as disk drives, dot
matrix printers and robotics.
Stepper motors commonly have a permanent magnet rotor surrounded
by a stator. The most common stepper motors have four stator
windings that are paired with a center-tapped common. This type of
stepper motor is commonly referred to as a four-phase or unipolar
stepper motor. The center tap allows a change of current direction
in each of the two coils when a winding is grounded, thereby
resulting in a polarity change of the stator.The direction of the
rotation is dictated by the stator poles. The stator poles are
determined by the current sent through the wire coils. As the
direction of the current is changed, the polarity is also changed
causing the reverse motion of the rotor.
It should be noted that while a conventional motor shaft runs
freely, the stepper motor shaft moves in a fixed repeatable
increment, which allows one to move it to a precise position. Thus,
the stepper motor moves one step when the direction of current flow
in the field coil(s) changes, reversing the magnetic field of the
stator poles. The difference between unipolar and bipolar motors
lies in the may that this reversal is achieved.
Fig10: Stepper motor operation
7.1 Advantages:
1. The rotation angle of the motor is proportional to the input
pulse.
2. The motor has full torque at standstill (if the windings are
energized)
3. Precise positioning and repeatability of movement since good
stepper motors have an accuracy of 3 5% of a step and this error is
non cumulative from one step to the next.
4. Excellent response to starting/ stopping/reversing.
5. Very reliable since there are no contact brushes in the
motor. Therefore the life of the motor is simply dependant on the
life of the bearing.
6. The motors response to digital input pulses provides
open-loop control, making the motor simpler and less costly to
control.
7. It is possible to achieve very low speed synchronous rotation
with a load that is directly coupled to the shaft.
8. A wide range of rotational speeds can be realized as the
speed is proportional to the frequency of the input pulses.7.2
Disadvantages:1. Resonances can occur if not properly
controlled.
2. Not easy to operate at extremely high speeds.7.3 Open Loop
Operation:One of the most significant advantages of a stepper motor
is its ability to be accurately controlled in an open loop system.
Open loop control means no feedback information about position is
needed. This type of control eliminates the need for expensive
sensing and feedback devices such as optical encoders. 7.4 Stepper
Motor Types:There are three basic stepper motor types. They
are:
Variable-reluctance
Permanent-magnet
Hybrid7.5 Variable-reluctance (VR):This type of stepper motor
has been around for a long time. It is probably the easiest to
understand from a structural point of view. This type of motor
consists of a soft iron multi-toothed rotor and a wound stator.
When the stator windings are energized with DC current, the poles
become magnetized. Rotation occurs when the rotor teeth are
attracted to the energized stator poles.
Fig 11: Cross-section of a variable reluctance (VR) motor.7.6
Permanent Magnet (PM)The permanent magnet step motor is a low cost
and low resolution type motor with typical step angles of 7.5 to
15. (48 24 steps/revolution) PM motors as the name implies have
permanent magnets added to the motor structure. In this type of
motor, the rotor does not have teeth. Instead the rotor is
magnetized with alternating north and south poles situated in a
straight line parallel to the rotor shaft. These magnetized rotor
poles provide an increased magnetic flux intensity and because of
this the PM motor exhibits improved torque characteristics when
compared with the VR type.
Fig12: PM stepper motor principle Fig13: Cross section of a
hybrid stepper motor7.7 Hybrid (HB):The hybrid stepper motor is
more expensive than the PM stepper motor but provides better
performance with respect to step resolution, torque and speed.
Typical step angles for the HB stepper motor range from 3.6 to 0.9
(100 400 steps per revolution). The hybrid stepper motor combines
the best features of both the PM and VR type stepper motors. The
rotor is multi-toothed like the VR motor and contains an axially
magnetized concentric magnet around its shaft. The teeth on the
rotor provide an even better path which helps guide the magnetic
flux to preferred locations in the air gap. This further increases
the detent, holding and dynamic torque characteristics of the motor
when compared with both the VR and PM types. This motor type has
some advantages such as very low inertia and a optimized magnetic
flow path with no coupling between the two stator windings. These
qualities are essential in some applications.7.8 When to Use a
Stepper Motor:
A stepper motor can be a good choice whenever controlled
movement is required. They can be used to advantage in applications
where you need to control rotation angle, speed, position and
synchronism. Because of the inherent advantages listed previously,
stepper motors have found their place in many different
applications.7.9 The Rotating Magnetic Field:When a phase winding
of a stepper motor is energized with current a magnetic flux is
developed in the stator. The direction of this flux is determined
by the Right Hand Rule which states:
If the coil is grasped in the right hand with the fingers
pointing in the direction of the current in the winding (the thumb
is extended at a 90 angle to the fingers), then the thumb will
point in the direction of the magnetic field.The below figure shows
the magnetic flux path developed when phase B is energized with
winding current in the direction shown. The rotor then aligns
itself so that the flux opposition is minimized. In this case the
motor would rotate clockwise so that its south pole aligns with the
north pole of the stator B at position 2 and its north pole aligns
with the south pole of stator B at position 6. To get the motor to
rotate we can now see that we must provide a sequence of energizing
the stator windings in such a fashion that provides a rotating
magnetic flux field which the rotor follows due to magnetic
attraction.
Fig14: Magnetic flux path through a two-pole stepper motor with
a lag between the rotor and stator.7.10 Torque Generation:The
torque produced by a stepper motor depends on several factors.
The step rate
The drive current in the windings
The drive design or type
In a stepper motor, a torque will be developed when the magnetic
fluxes of the rotor and stator are displaced from each other. The
stator is made up of a high permeability magnetic material. The
presence of this high permeability material causes the magnetic
flux to be confined for the most part to the paths defined by the
stator structure. This serves to concentrate the flux at the stator
poles. The torque output produced by the motor is proportional to
the intensity of the magnetic flux generated when the winding is
energized.
The basic relationship which defines the intensity of the
magnetic flux is defined by:
H = (N * i) / l
WhereN = the number of winding turns
i = current
H = Magnetic field intensity
l = Magnetic flux path length
This relationship shows that the magnetic flux intensity and
consequently the torque is proportional to the number of winding
turns and the current and inversely proportional to the length of
the magnetic flux path. Thus from this basic relationship it is
concluded that the same frame size stepper motor could have very
different torque output capabilities simply by changing the winding
parameters.7.11 Step Angle Accuracy:The main reason that the
stepper motor gained such popularity as a positioning device is for
its accuracy and repeatability. Typically stepper motors will have
a step angle accuracy of 3 5% of one step. This error is also non
cumulative from step to step. The accuracy of the stepper motor is
mainly a function of the mechanical precision of its parts and
assembly.
Fig15: Positional accuracy of a stepper motor
7.12 Torque versus Speed Characteristics:
The torque versus speed characteristics are the key to selecting
the right motor and drive method for a specific application. These
characteristics are dependent upon (change with) the motor,
excitation mode and type of driver or drive method.
Fig16: Torque versus speed characteristics7.13 Single Step
Response and Resonances:Stepper motors can often exhibit a
phenomena referred to as resonance at certain step rates. This can
be seen as a sudden loss or drop in torque at certain speeds which
can result in missed steps or loss of synchronism. It occurs when
the input step pulse rate coincides with the natural oscillation
frequency of the rotor. Often there is a resonance area around the
100 200 pps region and also one in the high step pulse rate region.
The resonance phenomenon of a stepper motor comes from its basic
construction and therefore it is not possible to eliminate it
completely. It is also dependent upon the load conditions. It can
be reduced by driving the motor in half or micro stepping
modes.
Fig17: Single step response versus time7.14 Definitions related
to stepper motor:
1. Step angle:Step angle is associated with the internal
construction of the motor, in particular the number of teeth on the
stator and the rotor.The step angle is the minimum degree of
rotation associated with a single step.
Step angleSteps per Revolution
0.72500
1.8200
2.0180
2.5144
5.072
7.548
1524
Table 2: Stepper motor step angles2. Steps per second and rpm
relation:The relation between rpm (revolutions per minute), steps
per revolution and steps per second is as follows: Steps per second
= (rpm*steps per revolution)/60
3. Motor speed:
The motor speed, measured in steps per second (steps/sec) is a
function of the switching rate.
4. Holding torque:
The amount of torque, from an external source, required to break
away the shaft from its holding position with the motor shaft
standstill or zero rpm condition.
7.15 STEPPER MOTOR INTERFACING WITH MICROCONTROLLER:
BLOCK DIAGRAM:
CHAPTER-8
RELAYS A relay is an electrically controllable switch widely
used in industrial controls, automobiles and appliances.
The relay allows the isolation of two separate sections of a
system with two different voltage sources i.e., a small amount of
voltage/current on one side can handle a large amount of
voltage/current on the other side but there is no chance that these
two voltages mix up.
Fig18: Circuit symbol of a relay
8.1 Operation:
When a current flow through the coil, a magnetic field is
created around the coil i.e., the coil is energized. This causes
the armature to be attracted to the coil. The armatures contact
acts like a switch and closes or opens the circuit. When the coil
is not energized, a spring pulls the armature to its normal state
of open or closed. There are all types of relays for all kinds of
applications.
Fig19: Relay Operation and use of protection diodes
Transistors and ICs must be protected from the brief high
voltage 'spike' produced when the relay coil is switched off. The
above diagram shows how a signal diode (eg 1N4148) is connected
across the relay coil to provide this protection. The diode is
connected 'backwards' so that it will normally not conduct.
Conduction occurs only when the relay coil is switched off, at this
moment the current tries to flow continuously through the coil and
it is safely diverted through the diode. Without the diode no
current could flow and the coil would produce a damaging high
voltage 'spike' in its attempt to keep the current flowing.
In choosing a relay, the following characteristics need to be
considered:
1. The contacts can be normally open (NO) or normally closed
(NC). In the NC type, the contacts are closed when the coil is not
energized. In the NO type, the contacts are closed when the coil is
energized.
2. There can be one or more contacts. i.e., different types like
SPST (single pole single throw), SPDT (single pole double throw)
and DPDT (double pole double throw) relay.
3. The voltage and current required to energize the coil. The
voltage can vary from a few volts to 50 volts, while the current
can be from a few milliamps to 20milliamps. The relay has a minimum
voltage, below which the coil will not be energized. This minimum
voltage is called the pull-in voltage.
4. The minimum DC/AC voltage and current that can be handled by
the contacts. This is in the range of a few volts to hundreds of
volts, while the current can be from a few amps to 40A or more,
depending on the relay.
8.2 DRIVING A RELAY:. In order to operate more than one relay,
ULN2003 can be connected between An SPDT relay consists of five
pins, two for the magnetic coil, one as the common terminal and the
last pins as normally connected pin and normally closed pin. When
the current flows through this coil, the coil gets energized.
Initially when the coil is not energized, there will be a
connection between the common terminal and normally closed pin. But
when the coil is energized, this connection breaks and a new
connection between the common terminal and normally open pin will
be established. Thus when there is an input from the
microcontroller to the relay, the relay will be switched on. Thus
when the relay is on, it can drive the loads connected between the
common terminals and normally open pin. Therefore, the relay takes
5V from the microcontroller and drives the loads which consume high
currents. Thus the relay acts as an isolation device. Digital
systems and microcontroller pins lack sufficient current to drive
the relay. While the relays coil needs around 10milli amps to be
energized, the microcontrollers pin can provide a maximum of
1-2milli amps current. For this reason, a driver such as ULN2003 or
a power transistor is placed in between the microcontroller and the
relay and microcontroller.8.3RELAY INTERFACING WITH THE
MICROCONTROLLER:
BLOCK DIAGRAM:
CHAPTER-9
DISPLAY COMPONENTS9.1 LIGHT DEPENDENT RESISTOR:
LDRs or Light Dependent Resistors are very useful especially in
light/dark sensor circuits. Normally the resistance of an LDR is
very high, sometimes as high as 1,000,000 ohms, but when they are
illuminated with light, the resistance drops dramatically.
Thus in this project, LDR plays an important role in controlling
the electrical appliances based on the intensity of light i.e., if
the intensity of light is more (during daytime) the loads will be
in off condition. And if the intensity of light is less (during
nights), the loads will be switched on.
9.2 LIQUID CRYSTAL DISPLAY:
LCD stands for Liquid Crystal Display. LCD is finding wide
spread use replacing LEDs (seven segment LEDs or other multi
segment LEDs) because of the following reasons:
1. The declining prices of LCDs.
2. The ability to display numbers, characters and graphics. This
is in contrast to LEDs, which are limited to numbers and a few
characters.
3. Incorporation of a refreshing controller into the LCD,
thereby relieving the CPU of the task of refreshing the LCD. In
contrast, the LED must be refreshed by the CPU to keep displaying
the data.
4. Ease of programming for characters and graphics.
These components are specialized for being used with the
microcontrollers, which means that they cannot be activated by
standard IC circuits. They are used for writing different messages
on a miniature LCD.
FunctionPin NumberNameLogic StateDescription
Ground1Vss-0V
Power supply2Vdd-+5V
Contrast3Vee-0 - Vdd
Control of operating4RS01 D0 D7 are interpreted as commandsD0 D7
are interpreted as data
5R/W01 Write data (from controller to LCD)Read data (from LCD to
controller)
6E01From 1 to 0 Access to LCD disabledNormal
operatingData/commands are transferred to LCD
Data / commands7D00/1Bit 0 LSB
8D10/1Bit 1
9D20/1Bit 2
10D30/1Bit 3
11D40/1Bit 4
12D50/1Bit 5
13D60/1Bit 6
14D70/1Bit 7 MSB
A model described here is for its low price and great
possibilities most frequently used in practice. It is based on the
HD44780 microcontroller (Hitachi) and can display messages in two
lines with 16 characters each. It displays all the alphabets, Greek
letters, punctuation marks, mathematical symbols etc. In addition,
it is possible to display symbols that user makes up on its own.
Automatic shifting message on display (shift left and right),
appearance of the pointer, backlight etc. are considered as useful
characteristics.9.2.1 Pins Functions
There are pins along one side of the small printed board used
for connection to the microcontroller. There are total of 14 pins
marked with numbers (16 in case the background light is built in).
Their function is described in the table below:9.2.2 LCD
screen:
LCD screen consists of two lines with 16 characters each. Each
character consists of 5x7 dot matrix. Contrast on display depends
on the power supply voltage and whether messages are displayed in
one or two lines. For that reason, variable voltage 0-Vdd is
applied on pin marked as Vee. Trimmer potentiometer is usually used
for that purpose. Some versions of displays have built in backlight
(blue or green diodes). When used during operating, a resistor for
current limitation should be used (like with any LE diode).9.2.3
LCD Basic Commands:All data transferred to LCD through outputs
D0-D7 will be interpreted as commands or as data, which depends on
logic state on pin RS:
RS = 1 - Bits D0 - D7 are addresses of characters that should be
displayed. Built in processor addresses built in map of characters
and displays corresponding symbols. Displaying position is
determined by DDRAM address. This address is either previously
defined or the address of previously transferred character is
automatically incremented.
RS = 0 - Bits D0 - D7 are commands which determine display mode.
List of commands which LCD recognizes are given in the table
below:CommandRSRWD7D6D5D4D3D2D1D0Execution Time
Clear display00000000011.64mS
Cursor home000000001x1.64mS
Entry mode set00000001I/DS40uS
Display on/off control0000001DUB40uS
Cursor/Display Shift000001D/CR/Lxx40uS
Function set00001DLNFxx40uS
Set CGRAM address0001CGRAM address40uS
Set DDRAM address001DDRAM address40uS
Read BUSY flag (BF)01BFDDRAM address-
Write to CGRAM or DDRAM10D7D6D5D4D3D2D1D040uS
Read from CGRAM or DDRAM11D7D6D5D4D3D2D1D040uS
Table3: List of commands which LCD recognizesI/D 1 = Increment
(by 1)
R/L 1 = Shift right 0 = Decrement (by 1)
0 = Shift left S 1 = Display shift on
DL 1 = 8-bit interface
0 = Display shift off
0 = 4-bit interface
D 1 = Display on
N 1 = Display in two lines
0 = Display off
0 = Display in one line
U 1 = Cursor on
F 1 = Character format 5x10 dots
0 = Cursor off
0 = Character format 5x7 dotsB 1 = Cursor blink on
D/C 1 = Display shift
0 = Cursor blink off
0 = Cursor shift9.2.4 LCD Connection:Depending on how many lines
are used for connection to the microcontroller, there are 8-bit and
4-bit LCD modes. The appropriate mode is determined at the
beginning of the process in a phase called initialization. In the
first case, the data are transferred through outputs D0-D7 as it
has been already explained. In case of 4-bit LED mode, for the sake
of saving valuable I/O pins of the microcontroller, there are only
4 higher bits (D4-D7) used for communication, while other may be
left unconnected. Consequently, each data is sent to LCD in two
steps: four higher bits are sent first (that normally would be sent
through lines D4-D7), four lower bits are sent afterwards. With the
help of initialization, LCD will correctly connect and interpret
each data received. Besides, with regards to the fact that data are
rarely read from LCD (data mainly are transferred from
microcontroller to LCD) one more I/O pin may be saved by simple
connecting R/W pin to the Ground. Such saving has its price. Even
though message displaying will be normally performed, it will not
be possible to read from busy flag since it is not possible to read
from display.9.2.5 LCD Initialization:
Once the power supply is turned on, LCD is automatically
cleared. This process lasts for approximately 15mS. After that,
display is ready to operate. The mode of operating is set by
default. This means that:
1. Display is cleared
2. Mode
DL = 1 Communication through 8-bit interface
N = 0 Messages are displayed in one line
F = 0 Character font 5 x 8 dots
3. Display/Cursor on/off
D = 0 Display off
U = 0 Cursor off
B = 0 Cursor blink off
4. Character entry
ID = 1 Addresses on display are automatically incremented by
1
S = 0 Display shift off Automatic reset is mainly performed
without any problems. Mainly but not always! If for any reason
power supply voltage does not reach full value in the course of
10mS, display will start perform completely unpredictably. If
voltage supply unit can not meet this condition or if it is needed
to provide completely safe operating, the process of initialization
by which a new reset enabling display to operate normally must be
applied.
Algorithm according to the initialization is being performed
depends on whether connection to the microcontroller is through 4-
or 8-bit interface. All left over to be done after that is to give
basic commands and of course- to display messages.
Fig 20: Procedure on 8-bit initialization.
9.2.6 LCD INTERFACING WITH THE MICROCONTROLLER:
BLOCK DIAGRAM:
CHAPTER-10
SWITCH AND LED INTERFACING WITH THE MICROCONTROLLER:
Switches and LEDs are the most widely used input/output devices
of the 8051.
10.1 SWITCH INTERFACING:
CPU accesses the switches through ports. Therefore these
switches are connected to a microcontroller. This switch is
connected between the supply and ground terminals. A single
microcontroller (consisting of a microprocessor, RAM and EEPROM and
several ports all on a single chip) takes care of hardware and
software interfacing of the switch.
These switches are connected to an input port. When no switch is
pressed, reading the input port will yield 1s since they are all
connected to high (Vcc). But if any switch is pressed, one of the
input port pins will have 0 since the switch pressed provides the
path to ground. It is the function of the microcontroller to scan
the switches continuously to detect and identify the switch
pressed.
The switches that we are using in our project are 4 leg micro
switches of momentary type.
Vcc R Fig21: Interfacing switch with the microcontrollerThus now
the two conditions are to be remembered:
1. When the switch is open, the total supply i.e., Vcc appears
at the port pin P2.0
P2.0 = 1
2. When the switch is closed i.e., when it is pressed, the total
supply path is provided to ground. Thus the voltage value at the
port pin P2.0 will be zero.
P2.0 = 0
By reading the pin status, the microcontroller identifies
whether the switch is pressed or not. When the switch is pressed,
the corresponding related to this switch press written in the
program will be executed.
10.2 LED INTERFACING:
LED stands for Light Emitting Diode.
Microcontroller port pins cannot drive these LEDs as these
require high currents to switch on. Thus the positive terminal of
LED is directly connected to Vcc, power supply and the negative
terminal is connected to port pin through a current limiting
resistor.
This current limiting resistor is connected to protect the port
pins from sudden flow of high currents from the power supply.
Thus in order to glow the LED, first there should be a current
flow through the LED. In order to have a current flow, a voltage
difference should exist between the LED terminals. To ensure the
voltage difference between the terminals and as the positive
terminal of LED is connected to power supply Vcc, the negative
terminal has to be connected to ground. Thus this ground value is
provided by the microcontroller port pin. This can be achieved by
writing an instruction CLR P1.0. With this, the port pin P1.0 is
initialized to zero and thus now a voltage difference is
established between the LED terminals and accordingly, current
flows and therefore the LED glows. LED and switches can be
connected to any one of the four port pins.
Fig22: LED interfacing with the microcontroller
Fig23: Schematic diagram
ADVANTAGES: A major advantage of a lighting control system over
conventional individualswitching Switching is the ability to
control any light, group of lights, or all lights in a building
from a single user interface device.
Any light or device can be controlled from any location. Reduces
emissioncarbon footprints.
A lighting scene can create dramatic changes in atmosphere, for
aresidenceor thestage, by a simple button press
APPLICATIONS:
Used in Inlandscape design landscape lighting fountainpumps
water spaheating
swimming poolcovers
motorizedgates outdoor fireplaceignition can be remotely or
automatically controlledCONCLUSION
CONCLUSION
Our project is a standalone AUTOMATIC ROOM LIGHT CONTROL WITH
VISITOR COUNTING FOR POWER SAVING APPLICATIONS IN SEMINAR HALLS.
Use of embedded technology makes this closed loop feedback control
system efficient and reliable. Micro controller (AT89S52) allows
dynamic and faster control. Liquid crystal display (LCD) makes the
system user-friendly. AT89S52 micro controller is the heart of the
circuit as it controls all the functions. RESULTS
RESULT
LDR is placed outside the room and is used to identify whether
it is day or night time. Whenever a person tries to enter into the
room, the receiver of first IR pair identifies the person. Then the
microcontroller opens the door by rotating the stepper motor. After
the person had entered into the room completely, the door will be
closed automatically. The light is switched off even if anyone is
present inside the room during the day time. The light is switched
off even if anyone is present inside the room during the day time.
Similarly, the light is switched off if no one is there inside the
room or if it is night times. Thus, depending on the intensity of
light and the surrounding temperature, the required action is
performed by the microcontroller. LCD displays the number of
persons present inside the room.
REFERENCESREFERENCES:
1. Embedded System By Raj Kamal
2. 8052 Microcontroller And Embedded Systems By Mazzidi
3. Embedded real time systems By Dr. K.V.K.K.Prasad
4. 8086 micro processor interfacing By A.K.Roy
APPENDIX
1
Features
Compatible with MCS-51 Products
8K Bytes of In-System Programmable (ISP) Flash Memory
Endurance: 1000 Write/Erase Cycles
4.0V to 5.5V Operating Range
Fully Static Operation: 0 Hz to 33 MHz
Three-level Program Memory Lock
256 x 8-bit Internal RAM
32 Programmable I/O Lines
Three 16-bit Timer/Counters
Eight Interrupt Sources
Full Duplex UART Serial Channel
Low-power Idle and Power-down Modes
Interrupt Recovery from Power-down Mode
Watchdog Timer
Dual Data Pointer
Power-off Flag
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
Atmels high-density nonvolatile memory technology and is
compatible with the indus-
try-standard 80C51 instruction set and pinout. The on-chip Flash
allows the program
memory to be reprogrammed in-system or by a conventional
nonvolatile memory pro-
grammer. 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 con-
tents but freezes the oscillator, disabling all other chip
functions until the next interrupt
or hardware reset.
Rev. 1919A-07/01 8-bit
Microcontroller
with 8K Bytes
In-System
Programmable Flash
AT89S52 AT89S52 2
TQFP 1
2
3
4
5
6
7
8
9
10
11
33
32
31
30
29
28
27
26
25
24
23 44
43
42
41
40
39
38
37
36
35
34
12
13
14
15
16
17
18
19
20
21
22
(MOSI) P1.5
(MISO) P1.6
(SCK) P1.7
RST
(RXD) P3.0
NC
(TXD) P3.1
(INT0) P3.2
(INT1) P3.3
(T0) P3.4
(T1) P3.5 P0.4 (AD4)
P0.5 (AD5)
P0.6 (AD6)
P0.7 (AD7)
EA/VPP
NC
ALE/PROG
PSEN
P2.7 (A15)
P2.6 (A14)
P2.5 (A13) P1.4
P1.3
P1.2
P1.1 (T2 EX)
P1.0 (T2)
NC
VCC
P0.0 (AD0)
P0.1 (AD1)
P0.2 (AD2)
P0.3 (AD3)
(WR) P3.6
(RD) P3.7
XTAL2
XTAL1
GND
GND
(A8) P2.0
(A9) P2.1
(A10) P2.2
(A11) P2.3
(A12) P2.4
PLCC 7
8
9
10
11
12
13
14
15
16
17
39
38
37
36
35
34
33
32
31
30
29 (MOSI) P1.5
(MISO) P1.6
(SCK) P1.7
RST
(RXD) P3.0
NC
(TXD) P3.1
(INT0) P3.2
(INT1) P3.3
(T0) P3.4
(T1) P3.5
P0.4 (AD4)
P0.5 (AD5)
P0.6 (AD6)
P0.7 (AD7)
EA/VPP
NC
ALE/PROG
PSEN
P2.7 (A15)
P2.6 (A14)
P2.5 (A13)
6
5
4
3
2
1
44
43
42
41
40
18
19
20
21
22
23
24
25
26
27
28
(WR) P3.6
(RD) P3.7
XTAL2
XTAL1
GND
NC
(A8) P2.0
(A9) P2.1
(A10) P2.2
(A11) P2.3
(A12) P2.4
P1.4
P1.3
P1.2
P1.1 (T2 EX)
P1.0 (T2)
NC
VCC
P0.0 (AD0)
P0.1 (AD1)
P0.2 (AD2)
P0.3 (AD3)
Pin Configurations
PDIP 1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21 (T2) P1.0
(T2 EX) P1.1
P1.2
P1.3
P1.4
(MOSI) P1.5
(MISO) P1.6
(SCK) P1.7
RST
(RXD) P3.0
(TXD) P3.1
(INT0) P3.2
(INT1) P3.3
(T0) P3.4
(T1) P3.5
(WR) P3.6
(RD) P3.7
XTAL2
XTAL1
GND
VCC
P0.0 (AD0)
P0.1 (AD1)
P0.2 (AD2)
P0.3 (AD3)
P0.4 (AD4)
P0.5 (AD5)
P0.6 (AD6)
P0.7 (AD7)
EA/VPP
ALE/PROG
PSEN
P2.7 (A15)
P2.6 (A14)
P2.5 (A13)
P2.4 (A12)
P2.3 (A11)
P2.2 (A10)
P2.1 (A9)
P2.0 (A8) AT89S52 3
Block Diagram PORT 2 DRIVERS
PORT 2
LATCH P2.0 - P2.7
FLASH
PORT 0
LATCH
RAM
PROGRAM
ADDRESS
REGISTER
BUFFER
PC
INCREMENTER
PROGRAM
COUNTER
DUAL DPTR
INSTRUCTION
REGISTER B
REGISTER
INTERRUPT, SERIAL PORT,
AND TIMER BLOCKS
STACK
POINTER
ACC
TMP2
TMP1
ALU PSW
TIMING
AND
CONTROL
PORT 1 DRIVERS
P1.0 - P1.7
PORT 3
LATCH
PORT 3 DRIVERS
P3.0 - P3.7
OSC
GND
V
CC
PSEN
ALE/PROG
EA / V
PP RST RAM ADDR.
REGISTER PORT 0 DRIVERS
P0.0 - P0.7 PORT 1
LATCH WATCH
DOG ISP
PORT
PROGRAM
LOGIC AT89S52 4
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 program-
ming and outputs the code bytes during program verifica-
tion. 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 (I ) because of the internal pullups.
IL
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.
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 (I ) because of the internal pullups.
IL
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.
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 (I ) because of the pullups.
IL
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 pro-
gramming and verification.
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/PROGAddress 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 dur-
ing a MOVX or MOVC instruction. Otherwise, the pin is
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 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) AT89S52 5
weakly pulled high. Setting the ALE-disable bit has no
effect if the microcontroller is in external execution mode.
PSENProgram Store Enable (PSEN) is the read strobe to exter-
nal program memory.
When the AT89S52 is executing code from external pro-
gram memory, PSEN is activated twice each machine
cycle, except that two PSEN activations are skipped during
each access to external data memory.
EA/VPP
External Access Enable. EA must be strapped to GND in
order to enable the device to fetch code from external pro-
gram memory locations starting at 0000H up to FFFFH.
Note, however, that if lock bit 1 is programmed, EA will be
internally latched on reset.
EA should be strapped to V
CC
for internal program execu-
tions.
This pin also receives the 12-volt programming enable volt-
age (V
PP
)
during Flash programming.
XTAL1
Input to the inverting oscillator amplifier and input to the
internal clock operating circuit.
XTAL2
Output from the inverting oscillator amplifier.
Table 1. AT89S52 SFR Map and Reset Values
0F8H
0FFH
0F0H
B
00000000
0F7H
0E8H
0EFH
0E0H
ACC
00000000
0E7H
0D8H
0DFH
0D0H
PSW
00000000
0D7H
0C8H
T2CON
00000000
T2MOD
XXXXXX00
RCAP2L
00
000000
RCAP2H
0
0000000
TL2
0000000
0
TH2
00000000
0CFH
0C0H
0C7H
0B8H
IP
XX000000
0BFH
0B0H
P3
11111111
0B7H
0A8H
IE
0X000000
0AFH
0A0H
P2
11111111
AUXR1
XXXXXXX0
WDTRST
XXXXXXXX
0A7H
98H
SCON
00000000
SBUF
XXXXXXXX
9FH
90H
P1
11111111
97H
88H
TCON
00000000
TMOD
00000000
TL0
00
000000
TL1
0
0000000
TH0
0000000
0
TH1
00000000
AUXR
XXX00XX0
8FH
80H
P0
11111111
SP
00000111
DP0L
00
000000
DP0H
0
0000000
DP1L
0000000
0
DP1H
00000000
PCON
0XXX0000
87H AT89S52 6
Special Function Registers
A map of the on-chip memory area called the Special Func-
tion Register (SFR) space is shown in Table 1.
Note that not all of the addresses are occupied, and unoc-
cupied 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 indetermi-
nate effect.
User software should not write 1s to these unlisted loca-
tions, 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 cap-
ture 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.
Table 2. T2CON Timer/Counter 2 Control Register
T2CON Address = 0C8H
Reset Value = 0000 0000B
Bit Addressable
Bit
TF2
EXF2
RCLK
TCLK
EXEN2
TR2
C/T2CP/RL276543210 Symbol
Function
TF2
Timer 2 overflow flag set by a Timer 2 overflow and must be
cleared by software. TF2 will not be set when either RCLK = 1
or TCLK = 1.
EXF2
Timer 2 external flag set when either a capture or reload is
caused by a negative transition on T2EX and EXEN2 = 1.
When Timer 2 interrupt is enabled, EXF2 = 1 will cause the CPU
to vector to the Timer 2 interrupt routine. EXF2 must be
cleared by software. EXF2 does not cause an interrupt in up/down
counter mode (DCEN = 1).
RCLK
Receive clock enable. When set, causes the serial port to use
Timer 2 overflow pulses for its receive clock in serial port
Modes 1 and 3. RCLK = 0 causes Timer 1 overflow to be used for
the receive clock.
TCLK
Transmit clock enable. When set, causes the serial port to use
Timer 2 overflow pulses for its transmit clock in serial port
Modes 1 and 3. TCLK = 0 causes Timer 1 overflows to be used for
the transmit clock.
EXEN2
Timer 2 external enable. When set, allows a capture or reload to
occur as a result of a negative transition on T2EX if Timer
2
is not being used to clock the serial port. EXEN2 = 0 causes
Timer 2 to ignore events at T2EX.
TR2
Start/Stop control for Timer 2. TR2 = 1 starts the timer.
C/T2Timer or counter select for Timer 2. C/T2 = 0 for timer
function. C/T2 = 1 for external event counter (falling edge
triggered). CP/RL2Capture/Reload select. CP/RL2 = 1 causes captures
to occur on negative transitions at T2EX if EXEN2 = 1. CP/RL2 = 0
causes automatic reloads to occur when Timer 2 overflows or
negative transitions occur at T2EX when EXEN2 = 1. When
either RCLK or TCLK = 1, this bit is ignored and the timer is
forced to auto-reload on Timer 2 overflow. AT89S52 7
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.
The user should always initialize the DPS bit to the
appropriate value before accessing the respective Data
Pointer Register.
Power Off Flag: The Power Off Flag (POF) is located at bit
4 (PCON.4) in the PCON SFR. POF is set to 1 during
power up. It can be set and rest under software control and
is not affected by reset.
Table 3a. AUXR: Auxiliary Register
AUXR
Address = 8EH
Reset Value = XXX00XX0B
Not Bit Addressable
WDIDLE
DISRTO
DISALE
Bit
7
6
5
4
3
2
1
0
Reserved for future expansion
DISALE
Disable/Enable ALE
DISALE
Operating Mode
0
ALE is emitted at a constant rate of 1/6 the oscillator
frequency
1
ALE is active only during a MOVX or MOVC instruction
DISRTO
Disable/Enable Reset out
DISRTO
0
Reset pin is driven High after WDT times out
1
Reset pin is input only
WDIDLE
Disable/Enable WDT in IDLE mode
WDIDLE
0
WDT continues to count in IDLE mode
1
WDT halts counting in IDLE mode Table 3b. AUXR1: Auxiliary
Register 1
AUXR1
Address = A2H
Reset Value = XXXXXXX0B
Not Bit Addressable
DPS
Bit
7
6
5
4
3
2
1
0
Reserved for future expansion
DPS
Data Pointer Register Select
DPS
0
Selects DPTR Registers DP0L, DP0H
1
Selects DPTR Registers DP1L, DP1H AT89S52 8
Memory Organization
MCS-51 devices have a separate address space for Pro-
gram 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 V
CC
, 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.
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 avail-
able as stack space.
AT89S52 9
Watchdog Timer
(One-time Enabled with Reset-out)
The WDT is intended as a recovery method in situations
where the CPU may be subjected to software upsets. The
WDT consists of a 13-bit counter and the Watchdog Timer
Reset (WDTRST) SFR. The WDT is defaulted to disable
from exiting reset. To enable the WDT, a user must write
01EH and 0E1H in sequence to the WDTRST register
(SFR location 0A6H). When the WDT is enabled, it will
increment every machine cycle while the oscillator is run-
ning. The WDT timeout period is dependent on the external
clock frequency. There is no way to disable the WDT
except through reset (either hardware reset or WDT over-
flow reset). When WDT overflows, it will drive an output
RESET HIGH pulse at the RST pin.
Using the WDT
To enable the WDT, a user must write 01EH and 0E1H in
sequence to the WDTRST register (SFR location 0A6H).
When the WDT is enabled, the user needs to service it by
writing 01EH and 0E1H to WDTRST to avoid a WDT over-
flow. The 13-bit counter overflows when it reaches 8191
(1FFFH), and this will reset the device. When the WDT is
enabled, it will increment every machine cycle while the
oscillator is running. This means the user must reset the
WDT at least every 8191 machine cycles. To reset the
WDT the user must write 01EH and 0E1H to WDTRST.
WDTRST is a write-only register. The WDT counter cannot
be read or written. When WDT overflows, it will generate an
output RESET pulse at the RST pin. The RESET pulse
duration is 96xTOSC, where TOSC=1/FOSC. To make the
best use of the WDT, it should be serviced in those sec-
tions of code that will periodically be executed within the
time required to prevent a WDT reset.
WDT During Power-down and Idle
In Power-down mode the oscillator stops, which means the
WDT also stops. While in Power-down mode, the user
does not need to service the WDT. There are two methods
of exiting Power-down mode: by a hardware reset or via a
level-activated external interrupt which is enabled prior to
entering Power-down mode. When Power-down is exited
with hardware reset, servicing the WDT should occur as it
normally does whenever the AT89S52 is reset. Exiting
Power-down with an interrupt is significantly different. The
interrupt is held low long enough for the oscillator to
stabi-
lize. When the interrupt is brought high, the interrupt is
serviced. To prevent the WDT from resetting the device
while the interrupt pin is held low, the WDT is not started
until the interrupt is pulled high. It is suggested that the
WDT be reset during the interrupt service for the interrupt
used to exit Power-down mode.
To ensure that the WDT does not overflow within a few
states of exiting Power-down, it is best to reset the WDT
just before entering Power-down mode.
Before going into the IDLE mode, the WDIDLE bit in SFR
AUXR is used to determine whether the WDT continues to
count if enabled. The WDT keeps counting during IDLE
(WDIDLE bit = 0) as the default state. To prevent the WDT
from resetting the AT89S52 while in IDLE mode, the user
should always set up a timer that will periodically exit
IDLE,
service the WDT, and reenter IDLE mode.
With WDIDLE bit enabled, the WDT will stop to count in
IDLE mode and resumes the count upon exit from IDLE.
UART
The UART in the AT89S52 operates the same way as the
UART in the AT89C51 and AT89C52. For further informa-
tion on the UART operation, refer to the ATMEL Web site
(http://www.atmel.com). From the home page, select Prod-
ucts, then 8051-Architecture Flash Microcontroller, then
Product Overview.
Timer 0 and 1
Timer 0 and Timer 1 in the AT89S52 operate the same way
as Timer 0 and Timer 1 in the AT89C51 and AT89C52. For
further information on the timers operation, refer to the
ATMEL Web site (http://www.atmel.com). From the home
page, select Products, then 8051-Architecture Flash
Microcontroller, then Product Overview.
Timer 2
Timer 2 is a 16-bit Timer/Counter that can operate as either
a timer or an event counter. The type of operation is
selected by bit C/T2 in the SFR T2CON (shown in Table 2).
Timer 2 has three operating modes: capture, auto-reload
(up or down counting), and baud rate generator. The
modes are selected by bits in T2CON, as shown in Table 3.
Timer 2 consists of two 8-bit registers, TH2 and TL2. In the
Timer function, the TL2 register is incremented every
machine cycle.