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GSM BASED DC MOTOR SPEED CONTROL
1. INTRODUCTION
This project mainly deals with the speed control of a DC
Motor using a GSM. The type of speed control that has been chosen here is pulse
width modulation PWM. This project deals with development of DC MOTOR
control using PC using PWM. 12V DC Motor drives widely use Micro controllers
and The project detail design and complete hardware based high performance DC
drive control system will be implemented. Most recently new requirements have
arisen. These include faster torque control update with flexible design capability of
motion peripherals for high performance military drive applications. Pulse width
modulation type of speed control is chosen here because of high accuracy, high
reliability, quick response and high efficiency.
Our project deals with the types of problems that we face due to disturbances
in supply voltage or load on the motor and enables us to overcome these
difficulties by helping us with the appropriate software and hardware.
We propose to design an embedded controller that helps us maintain the
speed of the DC machine within the specific limits and a remote operate the
embedded controller. Here, the pulses from the remote are sensed by sensor and
are transmitted to the embedded controller. This controller contains a
programmable PWM port. The output of this PWM port is used to control power
delivered by a power regulating device.
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1.1. HARDWARE COMPONENTS:
1. POWERSUPPLY UNIT
(TRANSFORMER, 7805 & 7812 REGULATORS, CAPACITOR 1000mf)
2. 89C52 MICROCONTROLLER
3. DC MOTOR
4. ULN 2803 DRIVER IC
5. DB 9 CONNECTOR
6. MAX 232 IC
1.2. SOFTWARE:
Soft Ware developed for this project in Embedded ‘C’ using KEIL-3.
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BLOCK DIAGRAM:
.
2. EMBEDDED SYSTEMS
2.1. DEFINITIONS:
Embedded system is a combination of hardware and software, it is also named
as “Firm ware”.
AT89C52
Micro
controller
unit
DTMF
HT9170B
POWER
SUPPLY
SUPPLY
MOBILE
(GSM)
MOTOR
DRIVER
DC MOTOR MOBILE
CONNECTIONNR
4
An embedded system is a special purpose computer system, which is
completely encapsulated by the device it controls. It is a computer-controlled
system.
An embedded system is a specialized system that is a part of a larger system
or machine. As a part of a larger system it largely determines its functionality.
Embedded systems are electronic devices that incorporate microprocessors with in
their implementations. The main purpose of the microprocessors are simplify the
system design and improve flexibility. In the embedded systems, the software is
often stored in a read only memory (RAM) chip.
Embedded systems provide several major functions including monitoring of
the analog environment by reading data from sensors and controlling actuators.
Inputs (sensor) Outputs (actuator)
Figure: A real time system interacts with environment
Embedded
System
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2.2. EXAMPLES OF EMBEDDED SYSTEMS:
Embedded systems are found in wide range of application areas. Originally they
were used only for expensive industrial control applications, but as technology
brought down the cost of dedicated processors, they began to appear in
moderately expensive applications such as automobiles, communication and
office equipments and television Today's embedded systems are so inexpensive
that they are used in almost every electronic product in our life. Embedded
systems are often designed for mass production.
Some examples of embedded systems:
Automatic Teller Machines
Cellular telephone and telephone switches
Computer network equipment
Computer printers
Disk drives
Engine controllers and antilock break controllers for automobiles
Home automation products
Handheld calculators
Household appliances
Medical equipment
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Measurement equipment
Multifunction wrist watches
Multifunction printers
Mobile phones with additional capabilities
Programmable Logic Controllers
3. BLOCK DIAGRAM
`
3.1. MICROPROCESSOR AND MICROCONTROLLER
Microprocessors and microcontrollers are used in embedded system products.
An embedded product uses a microprocessor (or microcontroller) to do one task and
one task only. Microprocessor as the term come to be known is a general purpose
89C52
HT
9170B
DRIVER
TRAIC
AC
MOTOR
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digital computer central processing unit. Although popularly known as a "computer
on chip", the microprocessor is in no sense a complete digital computer.
Microprocessor CPU contains Arithmetic Logical Unit, a program counter, a
stack pointer, some working registers, a clock timing circuits and interrupt
circuit. To make complete microcomputer memory must add, usually Read Only
Memory, Random Access Memory, memory decoders and an Input/output
devices. In addition special purpose devices such as interrupts, counters may be
added to relieve the CPU from time consuming counting or timing chores.
The hardware design of microprocessor CPU is arranged so that a small or very
large system can be configured around the CPU as the application demands. The
internal CPU architecture as well as the resultant machine level code that
operates that architecture is comprehensive but as flexible as possible.
The prime use of microprocessor is to read data perform extensive calculations
on that data and store those calculations in mass storage devices or display the
results for user use. The program is used by microprocessor are stored in the
mass storage devices and loaded into RAM as the user directs.
A microcontrollers is a computer on a single chip .Micro suggest that the device
is small and controller tells that the device is used to control objects, process or
events
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Microcontroller is a highly integrated chip that contains all the devices
comprising a computer. Typically this includes a CPU, RAM, Input/ Output
ports, timers, interrupts. So microcontroller is also called as "true computer on a
chip". Unlike a general purpose computer which also includes all of these
devices. A microcontroller is designed for a very specific task to control a
particular system.
A microcontroller is a general purpose device but one that is meant to read data,
performs limited calculations on that data and control its environment based on
those calculations.
The prime use of microcontroller is to control the operation of machine using
a fixed program that is stored in ROM that does not change over the life time of the
system.
The advantages of microcontroller over microprocessor are
cost is less
speed is more
power consumption is less
compact device
external components are minimum
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3.2. MICROPROCESSOR VERSES MICROCONTROLLER
The contrast between microprocessor and microcontroller is best exemplified by
the fact that:
Most microprocessor have operational codes for moving data from external
memory to CPU, microcontroller may have one or two.
Microprocessor may have one or two types of bit handling instructions
microcontroller will have many.
Microprocessor concerned with rapid movement of code and data from
external address to the chip, microcontroller is concerned with rapid data
movement of bits with in chip.
Microcontroller can function as a computer with out addition of external
devices, but microprocessor must have many additions to operate an
computer.
4. MICROCONTROLLER
4.1. A BRIEF HISTORY OF 8051:
In 1981, Intel Corporation introduced an 8 bit microcontroller called 8051.
This microcontroller had 128 bytes of RAM, 4K bytes of chip ROM, two timers, one
serial port, and four ports all on a single chip. At the time it was also referred as “A
SYSTEM ON A CHIP”.
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The 8051 is an 8-bit processor meaning that the CPU can work only on 8 bits
data at a time. Data larger than 8 bits has to be broken into 8 bits pieces to be
processed by the CPU. The 8051 has a total of four I\O ports each 8 bit wide.
There are many versions of 8051 with different speeds and amount of on-chip
ROM and they are all compatible with the original 8051. This means that if you
write a program for one it will run on any of them.
The 8051 is an original member of the 8051 family. There are two other members in
the 8051 family of microcontrollers. They are 8052 and 8031. All the three
microcontrollers will have the same internal architecture, but they differ in the
following aspects.
8031 has 128 bytes of RAM, two timers and 6 interrupts.
8051 has 4K ROM, 128 bytes of RAM, two timers and 6 interrupts.
8052 has 8K ROM, 128 bytes of RAM, three timers and 8 interrupts.
Of the three microcontrollers, 8051 is the most preferable. Microcontroller
supports both serial and parallel communication.
In the concerned project 8052 microcontroller is used. Here microcontroller
used is AT89C52, which is manufactured by ATMEL laboratories.
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4.2. Description of 89C52 Microcontroller:
The AT89C52 provides the following standard features: 8Kbytes of Flash,
256 bytes of RAM, 32 I/O lines, three 16-bit timer/counters, six-vector two-level
interrupt architecture, a full duplex serial port, on-chip oscillator, and clock circuitry.
In addition, the AT89C52 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.
By combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel
AT89C52 is a powerful microcomputer which provides a highly flexible and cost
effective solution to many embedded control applications.
4.3. Features of Microcontroller (8052)
Compatible with MCS-51 Products
8 Kbytes of In-System Reprogrammable Flash Memory
Endurance: 1,000 Write/Erase Cycles
Fully Static Operation: 0 Hz to 24 MHz
Three-Level Program Memory Lock
256 x 8-Bit Internal RAM
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32 Programmable I/O Lines
Three 16-Bit Timer/Counters
Eight vector two level Interrupt Sources
Programmable Serial Channel
Low Power Idle and Power Down Modes
In addition, the AT89C52 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.
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Block Diagram of Microcontroller
Figure 5.1 Block Diagram of 8052
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PIN CONFIGURATIONS
Figure Pin Diagram of 89C52
4.4. Pin Description
VCC
Pin 40 provides Supply voltage to the chip. The voltage source is +5v
GND.
Pin 20 is the grounded
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Port 0
Port 0 is an 8-bit open drain bidirectional I/O port from pin 32 to 39. 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 may 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 pull-ups.
Port 0 also receives the code bytes during Flash programming, and outputs the
code bytes during program verification. External pull-ups are required during
program verification.
Port 1
Port 1 is an 8-bit bidirectional I/O port with internal pull-ups from pin 1 to 8.
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 pull-ups and can be used as inputs.
As inputs, Port 1 pins that are externally being pulled low will source current (IIL)
because of the internal pull-ups. Port 1 also receives the low-order address bytes
during Flash programming and program verification.
Port 2
Port 2 is an 8-bit bidirectional I/O port with internal pull-ups from pin 21 to
28. The Port 2 output buffers can sink / source four TTL inputs. When 1s are written
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to Port 2 pins they are pulled high by the internal pull-ups and can be used as inputs.
As inputs, Port 2 pins that are externally being pulled low will source current (IIL)
because of the internal pull-ups.
Port 2 emits the high-order address byte during fetches from external program
memory and during accesses to external data memories that use 16-bit addresses
(MOVX @ DPTR). In this application it uses strong internal pull-ups when emitting
1s. During accesses to external data memory that uses 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 pull-ups from pin 10 to 17.
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 pull-ups and can be used as inputs.
As inputs, Port 3 pins that are externally being pulled low will source current (IIL)
because of the pull-ups.
Port 3 also serves the functions of various special features of the AT89C51 as
listed below:
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Table Special Features of 89C52
Port 3 also receives some control signals for Flash programming and
programming verification.
RST
Pin 9 is the Reset input. It is active high. Upon applying a high pulse to this
pin, the microcontroller will reset and terminate all activities. A high on this pin for
two machine cycles while the oscillator is running resets the device.
ALE/PROG
Address Latch is an output pin and is active high. Address Latch Enable 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.
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Note, however, that one ALE pulse is skipped during each access to external
Data Memory. If desired, ALE operation can be disabled by setting bit 0 of SFR
location 8EH. With the bit set, ALE is active only during a MOVX or MOVC
instruction. Otherwise, the pin is weakly pulled high. Setting the ALE-disable bit has
no effect if the microcontroller is in external execution mode.
PSEN
Program Store Enable is the read strobe to external program memory. When
the AT89C52 is executing code from external program memory, PSEN is activated
twice each machine cycle, except that two PSEN activations are skipped during each
access to external data memory.
EA/VPP
External Access Enable. EA must be strapped to GND in order to enable the
device to fetch code from external program memory locations starting at 0000H up
to FFFFH. Note, however, that if lock bit 1 is programmed, EA will be internally
latched on reset. EA should be strapped to VCC for internal program executions.
This pin also receives the 12-volt programming enable voltage (VPP) during Flash
programming, for parts that require 12-volt VPP.
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XTAL1
Input to the inverting oscillator amplifier and input to the internal clock
operating circuit.
XTAL2
Output from the inverting oscillator amplifier.
Oscillator Characteristics
XTAL1 and XTAL2 are the input and output, respectively; of an inverting
amplifier which can be configured for use as an on chip oscillator, as shown in
Figure either a quartz crystal or ceramic resonator may be used. To drive the device
from an external clock source, XTAL2 should be left unconnected while XTAL1 is
driven as shown in Figure 5.4.
Figure: crystal connections
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Figure: External Clock Drive Configuration
There are no requirements on the duty cycle of the external clock signal, since
the input to the internal clocking circuitry is through a divide-by two flip-flop, but
minimum and maximum voltage high and low time specifications must be observed.
TIMERS
Timer 0 and 1
Timer 0 and Timer 1 in the AT89C52 operate the same way as Timer 0 and
Timer 1 in the AT89C51.
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.
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
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5.2. Timer 2 consists of two 8-bit registers, TH2 and TL2. In the Timer function, the
TL2 register is incremented every machine cycle. Since a machine cycle consists of
12 oscillator periods, the count rate is 1/12 of the oscillator frequency.
Table Timer 2 Operating Modes
In the Counter function, the register is incremented in response to a 1-to-0
transition at its corresponding external input pin, T2. In this function, the external
input is sampled during S5P2 of every machine cycle. When the samples show a
high in one cycle and a low in the next cycle, the count is incremented. The new
count value appears in the register during S3P1 of the cycle following the one in
which the transition was detected. Since two machine cycles (24 oscillator periods)
are required to recognize a 1-to-0 transition, the maximum count rate is 1/24 of the
oscillator frequency. To ensure that a given level is sampled at least once before it
changes, the level should be held for at least one full machine cycle.
There are no restrictions on the duty cycle of external input signal, but it
should for at least one full machine to ensure that a given level is sampled at least
once before it changes
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Interrupts:
The AT89C52 has a total of six interrupt vectors: two external interrupts
(INT0 and INT1), three timer interrupts (Timers 0, 1, and 2), and the serial port
interrupt. These interrupts are all shown in Figure 5.5
Figure Interrupts source
Each of these interrupt sources can be individually enabled or disabled by setting
or clearing a bit in Special Function Register IE. IE also contains a global disable
bit, EA, which disables all interrupts at once.
Note that Table 5.3 shows that bit position IE.6 is unimplemented. In the
AT89C51, bit position IE.5 is also unimplemented. User software should not write
1s to these bit positions, since they may be used in future AT89 products.
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Table: Interrupts Enable Register
Timer 2 interrupt is generated by the logical OR of bits TF2 and EXF2 in
register T2CON. Neither of these flags is cleared by hardware when the service
routine is vectored
In fact, the service routine may have to determine whether it was TF2 or EXF2
that generated the interrupt, and that bit will have to be cleared in software.
The Timer 0 and Timer 1 flags, TF0 and TF1, are set at S5P2 of the cycle in
which the timers overflow. The values are then polled by the circuitry in the next
cycle. However, the Timer 2 flag, TF2, is set at S2P2 and is polled in the same
cycle in which the timer overflows.
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Idle Mode:
In idle mode, the CPU puts itself to sleep while all the on-chip peripherals
remain active. The mode is invoked by software. The content of the on-chip RAM
and all the special functions registers remain unchanged during this mode. The idle
mode can be terminated by any enabled interrupt or by a hardware reset. It should be
noted that when idle is terminated by a hardware reset, the device normally resumes
program execution, from where it left off, up to two machine cycles before the
internal reset algorithm takes control.
On-chip hardware inhibits access to internal RAM in this event, but access to
the port pins is not inhibited. To eliminate the possibility of an unexpected write to a
port pin when Idle is terminated by reset, the instruction following the one that
invokes Idle should not be one that writes to a port pin or to external memory.
Power down Mode:
In the power down mode the oscillator is stopped, and the instruction that
invokes power down is the last instruction executed. The on-chip RAM and Special
Function Registers retain their values until the power down mode is terminated. The
only exit from power down is a hardware reset. Reset redefines the SFRs but does
not change the on-chip RAM. The reset should not be activated before VCC is
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restored to its normal operating level and must be held active long enough to allow
the oscillator to restart and stabilize.
Table Status of External Pins during Idle and Power down Mode
Program Memory Lock Bits
On the chip are three lock bits which can be left unprogrammed (U) or can be
programmed (P) to obtain the additional features listed in the table 5.4. When lock
bit 1 is programmed, the logic level at the EA pin is sampled and latched during
reset. If the device is powered up without a reset, the latch initializes to a random
value, and holds that value until reset is activated. It is necessary that the latched
value of EA be in agreement with the current logic level at that pin in order for the
device to function properly.
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Table 5.4 Lock Bit Protection Modes
Programming the Flash
The AT89C51 is normally shipped with the on-chip Flash memory array in
the erased state (that is, contents = FFH) and ready to be programmed. The
programming interface accepts either a high-voltage (12-volt) or a low-voltage
(VCC) program enable signal. The low voltage programming mode provides a
convenient way to program the AT89C51 inside the user’s system, while the high-
voltage programming mode is compatible with conventional third party Flash or
EPROM programmers.
The AT89C52 is shipped with either the high-voltage or low voltage
programming mode enabled. The respective top-side marking and device signature
codes are listed in the following table.
27
Top side Marking and Device Signature Codes
The AT89C52 code memory array is programmed byte-by-byte in either
programming mode. To program any non-blank byte in the on-chip Flash Memory,
the entire memory must be erased using the Chip Erase Mode.
Programming Algorithm
Before programming the AT89C52, the address, data and control signals should
be set up according to the Flash programming mode table and Figures 3 and 4. To
program the AT89C52, take the following steps.
1. Input the desired memory location on the address lines.
2. Input the appropriate data byte on the data lines.
3. Activate the correct combination of control signals.
4. Raise EA/VPP to 12 V for the high-voltage programming mode.
5. Pulse ALE/PROG once to program a byte in the Flash array or the lock bits. The
byte-write cycle is self-timed and typically takes no more than 1.5 Ms. Repeat steps
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1 through 5, changing the address and data for the entire array or until the end of the
object file is reached.
Data Polling
The AT89C52 features Data Polling to indicate the end of a write cycle. During a
write cycle, an attempted read of the last byte written will result in the complement
of the written datum on PO.7. Once the write cycle has been completed, true data are
valid on all outputs, and the next cycle may begin. Data Polling may begin any time
after a write cycle has been initiated.
Ready/Busy
The progress of byte programming can also be monitored by the RDY/BSY
output signal. P3.4 is pulled low after ALE goes high during programming to
indicate BUSY. P3.4 is pulled high again when programming is done to indicate
READY.
Program Verify
If lock bits LB1 and LB2 have not been programmed, the programmed code
data can be read back via the address and data lines for verification. The lock bits
cannot be verified directly. Verification of the lock bits is achieved by observing that
their features are enabled.
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Chip Erase
The entire Flash array is erased electrically by using the proper combination of
control signals and by holding ALE/PROG low for 10 ms. The code array is written
with all "1"s. The chip erase operation must be executed before the code memory
can be re-programmed.
Reading the Signature Bytes
The signature bytes are read by the same procedure as a normal verification of
locations 030H, 031H, and 032H, except that P3.6 and P3.7 must be pulled to a
Logic low. The values returned are as follows.
(030H) = 1EH indicates manufactured by Atmel
(031H) = 51H indicates 89C51
(032H) = FFH indicates 12 V programming
(032H) = 05H indicates 5 V programming
Programming Interface
Every code byte in the Flash array can be written and the entire array can be
erased by using the appropriate combination of control signals. The write operation
cycle is self-timed and once initiated, will automatically time itself to completion.
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Table: Flash Programming Modes
5. PWM THE SOLUTION
PWM is a way of digitally encoding analog signal levels. Through the use of
high-resolution counters, the duty cycle of a square wave is modulated to encode a
specific analog signal level. The PWM signal is still digital because, at any given
instant of time, the full DC supply is either fully on or fully off. The voltage or
current source is supplied to the analog load by means of a repeating series of and
off pulse.
The on time is the time during which the DC supply is applied to the load and
the off time is the periods during which that supply is switched off. Given a
sufficient bandwidth, any analog value can be encoded with PWM.
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Many micro controllers include PWM controllers. For example,
Microchip’s PIC16C67 includes two, each of which has a selectable on-time and
period.
The duty cycle is the ratio of the on-time to the period.
5.1. ADVANTAGES OF PWM:
PWM is economical, space saving. The signal remains
digital all the way from the processor to the controlled system. No digital-to –analog
conversion is necessary. By keeping the signal digital, noise immunity is yet another
benefit of choosing PWM over analog control and is the principal reason PWM is
sometimes used for communication.
5.2APPLICATIONS OF PWM:
PWM is employed in a wide variety of applications, ranging from
Measurement and communication to power control and conversion. As a concrete
example consider a PWM-controlled brake. To put it simply, a brake is a device that
clamps down hard on something in many brakes; the amount of clamping pressure is
controlled with an analog input signal. The more voltage or current that’s applied to
the brake, the more pressure the brake will exert. The output of a PWM controller
could be connected to a switch between the supply and the brake to produce more
stopping power, the software need only increase the duty cycle of the PWM output.
5.3. Serial communication between PC and microcontroller
When a processor communicates with the outside world, it provides data
in byte sized chunks. Computers transfer data in two ways: parallel and serial. In
parallel data transfers, often more lines are used to transfer data to a device and 8 bit
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data path is expensive. The serial communication transfer uses only a single data line
instead of the 8 bit data line of parallel communication which makes the data
transfer not only cheaper but also makes it possible for two computers located in two
different cities to communicate over telephone.
Serial data communication uses two methods, asynchronous and
synchronous. The synchronous method transfers data at a time while the
asynchronous transfers a single byte at a time. There are some special IC chips made
by many manufacturers for data communications. These chips are commonly
referred to as UART (universal asynchronous receiver-transmitter) and USART
(universal synchronous asynchronous receiver transmitter). The AT89C51 chip has a
built in UART.
In asynchronous method, each character is placed between start and stop bits.
This is called framing. In data framing of asynchronous communications, the data,
such as ASCII characters, are packed in between a start and stop bit. We have a total
of 10 bits for a character: 8 bits for the ASCII code and 1 bit each for the start and
stop bits. The rate of serial data transfer communication is stated in bps or it can be
called as baud rate.
To allow the compatibility among data communication equipment made by
various manufacturers, and interfacing standard called RS232 was set by the
Electronics industries Association in 1960. Today RS232 is the most widely used
I/O interfacing standard. This standard is used in PCs and numerous types of
equipment. However, since the standard was set long before the advent of the TTL
logic family, its input and output voltage levels are not TTL compatible. In RS232, a
1 bit is represented by -3 to -25V, while a 0 bit is represented +3 to +25 V, making -
3 to +3 undefined. For this reason, to connect any RS232 to a microcontroller system
we must use voltage converters such as MAX232 to connect the TTL logic levels to
33
RS232 voltage levels and vice versa. MAX232 ICs are commonly referred to as line
drivers.
The RS232 cables are generally referred to as DB-9 connector. In
labeling, DB-9P refers to the plug connector (male) and DB-9S is for the socket
connector (female). The simplest connection between a PC and microcontroller
requires a minimum of three pin, TXD, RXD, and ground. Many of the pins of the
RS232 connector are used for handshaking signals. They are bypassed since they are
not supported by the 8051 UART chip.
IBM PC/ compatible computers based on x86(8086, 80286, 386, 486
and Pentium) microprocessors normally have two COM ports. Both COM ports have
RS232 type connectors. Many PCs use one each of the DB-25 and DB-9 RS232
connectors. The COM ports are designated as COM1 and COM2. We can connect
the serial port to the COM 2 port of a PC for serial communication experiments. We
use a DB9 connector in our arrangement.
The AT89C52 has two pins that are used specifically for transferring
and receiving data serially. These two pins are called TXD and RXD and are part of
the port3 (P3.0 and P3.1). These pins are TTL compatible; therefore they require a
34
line driver to make them RS232 compatible. One such line driver is the MAX232
chip. One advantage of MAX232 chip is that it uses a +5v power source which is the
same as the source voltage for the at89c51. The MAX232 has two sets of line drivers
for receiving and transferring data. The line drivers for TXD are called T1 and T2
while the line drivers for RXD are designated as R1 and R2. T1 and R1 are used for
TXD and RXD of the 89c51 and the second set is left unused. In MAX232 that the
TI line driver has a designation of T1 in and T1 out on pin numbers 11 and 14,
respectively. The T1 in pin is the TTL side and is connected to TXD of the
microcontroller, while TI out is the RS232 side that is connected to the RXD pin of
the DB9 connector.
To allow data transfer between PC and the microcontroller system
without any error, we must make sure that the baud rate of the 8051 system matches
the baud rate of the PC’s COM port.
6. ULN DC MOTOR DRIVER
ULN is mainly suited for interfacing between low-level circuits
and multiple peripheral power loads, The series ULN20XX high voltage, high
current Darlington arrays feature continuous load current ratings. The driving
circuitry in- turn decodes the coding and conveys the necessary data to the stepper
motor, this module aids in the movement of the arm through steppers.
35
The driver makes use of the ULN2003 driver IC, which contains an
array of 7 power Darlington arrays, each capable of driving 500mA of current. At
an approximate duty cycle, depending on ambient temperature and number of
drivers turned on, simultaneously typical power loads totaling over 230w can be
controlled.
The device has base resistors, allowing direct connection to any
common logic family. All the emitters are tied together and brought out to a
separate terminal. Output protection diodes are included; hence the device can
drive inductive loads with minimum extra components. Typical loads include
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relays, solenoids, stepper motors, magnetic print hammers, multiplexed LED,
incandescent displays and heaters.
6.1. The main features of ULN2003 are as follows:
Seven Darlington per package
Output current 500ma per driver (600ma peak)
Output voltage 50v
Integrated suppression diodes for inductive loads
Outputs can be paralleled for high current TTL/CMOS/DTL compatible inputs
Inputs pinned opposite outputs to simplify layout.
Transient protected outputs
Dual In-Line plastic package or small-Outline IC package.
7. DC MOTOR
DC motors are configured in many types and sizes, including brush less, servo,
and gear motor types. A motor consists of a rotor and a permanent magnetic field
stator. The magnetic field is maintained using either permanent magnets or
electromagnetic windings. DC motors are most commonly used in variable speed
and torque.
Motion and controls cover a wide range of components that in
some way are used to generate and/or control motion. Areas within this category
include bearings and bushings, clutches and brakes, controls and drives, drive
components, encoders and resolves, Integrated motion control, limit switches,
linear actuators, linear and rotary motion components, linear position sensing,
motors (both AC and DC motors), orientation position sensing, pneumatics and
pneumatic components, positioning stages, slides and guides, power transmission
37
(mechanical), seals, slip rings, solenoids, springs.
Motors are the devices that provide the actual speed and torque in a
drive system. This family includes AC motor types (single and multiphase motors,
universal, servo motors, induction, synchronous, and gear motor) and DC motors
(brush less, servo motor, and gear motor) as well as linear, stepper and air motors,
and motor contactors and starters.
In any electric motor, operation is based on simple
electromagnetism. A current-carrying conductor generates a magnetic field; when
this is then placed in an external magnetic field, it will experience a force
proportional to the current in the conductor, and to the strength of the external
magnetic field. As you are well aware of from playing with magnets as a kid,
opposite (North and South) polarities attract, while like polarities (North and
North, South and South) repel. The internal configuration of a DC motor is
designed to harness the magnetic interaction between a current-carrying conductor
and an external magnetic field to generate rotational motion.
Let's start by looking at a simple 2-pole DC electric motor (here red
represents a magnet or winding with a "North" polarization, while green represents
a magnet or winding with a "South" polarization).
Every DC motor has six basic parts -- axle, rotor (a.k.a., armature), stator,
commutator, field magnet(s), and brushes. In most common DC motors (and all
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that Beamers will see), the external magnetic field is produced by high-strength
permanent magnets1. The stator is the stationary part of the motor -- this includes
the motor casing, as well as two or more permanent magnet pole pieces. The rotor
(together with the axle and attached commutator) rotates with respect to the stator.
The rotor consists of windings (generally on a core), the windings being
electrically connected to the commutator. The above diagram shows a common
motor layout -- with the rotor inside the stator (field) magnets.
The geometry of the brushes, commutator contacts, and rotor
windings are such that when power is applied, the polarities of the energized
winding and the stator magnet(s) are misaligned, and the rotor will rotate until it is
almost aligned with the stator's field magnets. As the rotor reaches alignment, the
brushes move to the next commutator contacts, and energize the next winding.
Given our example two-pole motor, the rotation reverses the direction of current
through the rotor winding, leading to a "flip" of the rotor's magnetic field, and
driving it to continue rotating.
In real life, though, DC motors will always have more than two poles
(three is a very common number). In particular, this avoids "dead spots" in the
commutator. You can imagine how with our example two-pole motor, if the rotor
is exactly at the middle of its rotation (perfectly aligned with the field magnets), it
will get "stuck" there. Meanwhile, with a two-pole motor, there is a moment where
the commutator shorts out the power supply (i.e., both brushes touch both
commutator contacts simultaneously). This would be bad for the power supply,
waste energy, and damage motor components as well. Yet another disadvantage of
such a simple motor is that it would exhibit a high amount of torque” ripple" (the
amount of torque it could produce is cyclic with the position of the rotor).
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So since most small DC motors are of a three-pole design, let's tinker with the
workings of one via an interactive animation (JavaScript required):
You'll notice a few things from this -- namely, one pole is fully energized at a time
(but two others are "partially" energized). As each brush transitions from one
commutator contact to the next, one coil's field will rapidly collapse, as the next
coil's field will rapidly charge up (this occurs within a few microsecond). We'll see
more about the effects of this later, but in the meantime you can see that this is a
direct result of the coil windings' series wiring:
40
There's probably no better way to see how an average dc motor is put together,
than by just opening one up. Unfortunately this is tedious work, as well as
requiring the destruction of a perfectly good motor.
This is a basic 3-pole dc motor, with 2 brushes and three commutator contacts.
8. POWER SUPPLY
There are many types of power supply. Most are designed to convert high
voltage AC mains electricity to a suitable low voltage supply for electronics circuits
and other devices. A power supply can by broken down into a series of blocks, each
of which performs a particular function.
For example a 5V regulated supply can be shown as below
Fig 3.10: Block Diagram of a Regulated Power Supply System
41
Similarly, 12v regulated supply can also be produced by suitable selection of
the individual elements. Each of the blocks is described in detail below and the
power supplies made from these blocks are described below with a circuit diagram
and a graph of their output:
8.1. Transformer:
A transformer steps down high voltage AC mains to low voltage AC. Here we
are using a center-tap transformer whose output will be sinusoidal with 36volts peak
to peak value.
Fig: 3.10.2 Output Waveform of transformer
The low voltage AC output is suitable for lamps, heaters and special AC
motors. It is not suitable for electronic circuits unless they include a rectifier and a
smoothing capacitor. The transformer output is given to the rectifier circuit.
8.2. Rectifier:
A rectifier converts AC to DC, but the DC output is varying. There are several
types of rectifiers; here we use a bridge rectifier.
The Bridge rectifier is a circuit, which converts an ac voltage to dc
voltage using both half cycles of the input ac voltage. The Bridge rectifier circuit is
shown in the figure. The circuit has four diodes connected to form a bridge. The ac
42
input voltage is applied to the diagonally opposite ends of the bridge. The load
resistance is connected between the other two ends of the bridge.
For the positive half cycle of the input ac voltage, diodes D1 and D3 conduct,
whereas diodes D2 and D4 remain in the OFF state. The conducting diodes will be
in series with the load resistance RL and hence the load current flows through RL.
For the negative half cycle of the input ac voltage, diodes D2 and D4
conduct whereas, D1 and D3 remain OFF. The conducting diodes D2 and D4 will be
in series with the load resistance RL and hence the current flows through RL in the
same direction as in the previous half cycle. Thus a bi-directional wave is converted
into unidirectional.
FIG: The output waveform of the rectifier is shown as below
43
The varying DC output is suitable for lamps, heaters and standard motors. It is
not suitable for electronic circuits unless they include a smoothing capacitor.
8.3. Smoothing:
The smoothing block smoothes the DC from varying greatly to a small
ripple. The ripple voltage is defined as the deviation of the load voltage from its DC
value. Smoothing is also named as filtering.
Filtering is frequently effected by shunting the load with a capacitor. The
action of this system depends on the fact that the capacitor stores energy during the
conduction period and delivers this energy to the loads during the no conducting
period. In this way, the time during which the current passes through the load is
prolong Ted, and the ripple is considerably decreased. The action of the capacitor is
shown with the help of waveform.
Fig 3.10.4.1The waveform of the rectified output after smoothing is given below:
44
8.4. Regulator:
Regulator eliminates ripple by setting DC output to a fixed voltage. Voltage
regulator ICs are available with fixed (typically 5, 12 and 15V) or variable output
voltages. Negative voltage regulators are also available
Many of the fixed voltage regulator ICs has 3 leads (input, output and high
impedance). They include a hole for attaching a heat sink if necessary. Zener diode
is an example of fixed regulator which is shown here.
3.10.1 REGULATOR
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Transformer + Rectifier + Smoothing + Regulator:
9. HT9170B-- DTMF RECIEVER
The HT9170B/D are Dual Tone Multi Frequency (DTMF) receivers integrated
with digital decoder and band split filter functions as well as power-down mode and
inhibit mode operations. Such devices use digital counting techniques to detect and
decode all the 16 DTMF tone pairs into a 4-bit code output.
Highly accurate switched capacitor filters are implemented to divide tone signals
into low and high group signals. A built-in dial tone rejection circuit is provided to
eliminate the need for pre-filtering.
9.1. FEAUTURES:
Operating voltage: 2.5V~5.5V
Minimal external components
No external filter is required
Low standby current (on power down mode)
Excellent performance
Tristate data output for MCU interface
46
3.58MHz crystal or ceramic resonator
1633Hz can be inhibited by the INH pin
HT9170B: 18-pin DIP package
47
PIN ASSIGMENT:
PIN DESCRIPTION:
48
BLOCK DIAGRAM:
9.2. FUNCTIONAL DESCRIPTION:
The HT9170B/D tone decoders consist of three band pass filters and two
digital decode circuits to convert a tone (DTMF) signal into digital code output.
An operational amplifier is built-in to adjust the input signal. The pre-filter is a band
rejection filter, which reduces the dialing tone from 350Hz to 400Hz.
The low group filter filters low group frequency signal output whereas the high
group filter filters high group Frequency signal output. A zero-crossing detector with
follows each filters output hysteretic. When each signal amplitude at the output
exceeds the specified level, it is transferred to full swing logic signal.
49
When input signals are recognized to be effective, DV becomes high, and the correct
tone code (DTMF) digit is transferred.
Steering control circuit:
The steering control circuit is used for measuring the effective signal duration
and for protecting against drop out of valid signals. It employs the analog delay by
external RC time-constant controlled by EST.
The EST pin is normally low and draws the RT/GT pin to keep low through
discharge of external RC. When a valid tone input is detected, EST goes high to
charge RT/GT through RC.
When the voltage of RT/GT changes from 0 to VTRT (2.35V for 5V supply), the
input signal is effective, and the code detector will create the correct code. After
D0~D3 are completely latched, DV output becomes high. When the voltage of
RT/GT falls down from VDD to VTRT (i.e. when there is no input tone), DV output
becomes Low, and D0~D3 keeps data until a next valid tone input is produced. By
selecting adequate external RC value, the minimum acceptable input tone duration
(TACC) and the minimum acceptable inter-tone rejection (ITR) can be set. External
Components (R, C) are chosen by the formula.
TACC=TDP+TGTP;
ITR=TDP+TGTP;
Where tACC: Tone duration acceptable time
TDP: EST output delay time (_L__H_)
TGTP: Tone present time
TIR: Inter-digit pause rejection time
50
TDA: EST output delay time (_H__L_)
TGTA: Tone absent time
TIMING DIAGRAM
51
PIN DIAGRAMOF 8870:
Applications:
PABX
Central office
Mobile radio
Remote control
Remote data entry
Call limiting
Telephone answering systems
52
10. PROJECT CODE
*PROGRAM FOR PC BASED AC MOTOR SPEED CONTROL */
#include<reg52.h>
void delay(unsigned int val);
sbit mt=P1^1; //input dc motor
unsigned char z;
void main()
{
void delay(unsigned int val)
{
unsigned int x,y;
for(x=0;x<val;x++)
for(y=0;y<1275;y++);
}
while(1)
{
switch(P2)
{
case (0X31):
53
{
mt=1;
delay(10);
mt=0;
delay(90);
break;
}
case (0X32):
{
mt=1;
delay(20);
mt=0;
delay(80);
break;
}
case (0X33):
{
mt=1;
delay(30);
54
mt=0;
delay(70);
break;
}
case (0X35):
{
mt=0;
delay(0);
mt=1;
delay(100);
break;
}
case (0X39):
{
mt=0;
delay(100);
mt=1;
delay(0);
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break;
}
default:
{
mt=0;
}
while(1)
{
if(sw==1)
{
mt=1;
delay(50);
mt=0;
delay(50);
}
else
{
P1=0;
mt=0;
56
delay(20);
mt=1;
delay(80);
}
}
11. CONCLUSION
The speed control of DC Motor has been achieved successfully using
microcontroller unit. The circuit has been tested and verified.
We used DC MOTOR control to achieve various speed of the Motor, for this
fixed numbering is programmed by using the microcontroller. And the program has
been successfully tested and verified for several specified loads.
We can obtain various speed using this program and circuitry.
12. BIBILIOGRAPHY
1. The 8051 Microcontroller Architecture, Programming & Applications
…… Kenneth J Ayala
57
2. The 8051 Microcontroller & Embedded Systems
…… Mohammed Ali Mazidi &
Janice Gillispie Mazidi
3. Power Electronics
……. M D Singh &
K B Khanchandani
4. Linear Integrated Circuits
i. ……. D Roy Choudary & Shail Jain
5. Electrical Machines
i. …….. S K Bhattacharya
6. Electrical Machines II
i. …….. B L Thereja
13. REFERENCES
1. WWW.ELECTRONICS4U.COM
58
2. WWW.AARONCAKE.NET
3. WWW.MAZIDI.COM
4. WWW.8051PROJECTS.COM
