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.