Embed Size (px)
Citation preview
UNIT-V 5.1
UNIT 5
MICROCONTROLLER
APPLICATIONS
UNIT-V 5.2
CONTENTS
Technical Terms
5.1 Interfacing LCD Display
5.2 DAC Interface
5.2.1 Pin diagram & block diagram of DAC0800
5.2.2 Interfacing DAC0800 with 8031/8051 Microcontroller
5.3 Interfacing ADC
5.3.1 ADC0809
5.3.2 ADC0809 interfacing with 8051
5.4 Temperature Control
5.4.1 Microprocessor based temperature control system
5.5 Stepper Motor
5.5.1 Construction
5.5.2 Interfacing
5.6 Keyboard Interface
5.6.1 Key bounce using software
5.6.2 Simple keyboard Interface
5.6.3 Matrix Keyboard interface
5.7 Motor Speed Control System
5.7.1 DC motor (or) direct current motor
5.7.2 DC motor speed control
5.7.3 Pulse Width Modulation (PWM)
5.7.4 DC motor control using L293
5.7.5 DC motor control using Optoisolator
Question Bank
UNIT-V 5.3
TECHNICAL TERMS
1. Interface : Connection of external device to the microprocessor
2. LCD : Liquid Crystal Display
3. DAC : IC that converts the digital output of Microcontroller to Analog output
4. ADC : IC that converts the Analog input to the Microcontroller to Digital Input
5. Resolution : Minimum value that can be represented by the analog or digital data
UNIT-V 5.4
5.1 Interfacing LCD Display
Nowadays, many LCD modules are available which have build –in drives for LCD and
interfacing circuitry to interface then to microprocessor /microcontroller systems . These
LCD modules allow display of characters as well as numbers .They are available in
16x2,20x1,20x2,20x4 & 40x2sizes.The main advantage of using LCD is modules is that they
required very less power .The first figure represents number of character in each line and
second figure represents no of lines the display has. The interfacing of 20x2 LCD display to
microprocessor/microcontroller system through 8255 is discussed. In this module the display
is organized as two lines, each of 20 characters The module has 14 pins.
Fig 5.1: Liquid crystal display
The interfacing of a 20 character 2 line LCD module with the 8051 is shown. The data
lines are connected to the port 1 of 8051 and control lines RS, R/W and E are driven by 3.2,
3.3 and 3.4 lines of port 3, respectively .The voltage at V EE pin is adjusted by a
potentiometer to adjust the contrast of LCD.
UNIT-V 5.5
Fig 5.2: LCD interface with 8051
UNIT-V 5.6
To display a message on LCD module, it is necessary to initialize it by writing series of
command codes in the command in the register in the proper sequence .The initialization
cursor automatically after writing a character. After initialization we can write data to either
DD RAM or CG RAM. Both RAMs are read/write RAMS an have unique addresses to
access each location. To write data in any RAM we have to set the address for that RAM by
issuing proper commands. Then we can write data into it by activating write cycle . To
activate write cycle we have to make R/W signal low, RS signal high, send data on port A
and apply high to low pulse of at least 450 ns of duration on E pin of the module .The DD
RAM stores the character in their ASCII code whereas CG RAM stores the character in its
internally generated character code .Let us see the 805 assembly language program to display
‘WELCOME’ message on the LC module .Before sensing command or data it is necessary to
check busy flag , i.e. whether LCD us reading or not .
Main Routine:
MOV 81H, #30h Initialise stack pointer
MOV A, #3Ch send command code to set font
LCALL COMMAND
MOV A, #OEh send command code to set display
LCALL COMMAND
MOV A, #O1h send command code to clear LCD
LCALL COMMAND
MOV A, #86h send command code set DD RAM
LCALL COMMAND
MOV A, ‘W’ Display lettter W
LCALL DISPLAY
MOV A, ‘E’ Display lettter E
LCALL DISPLAY
MOV A, ‘L’ Display lettter L
LCALL DISPLAY
MOV A, ‘C’
LCALL DISPLAY Display lettter C
MOV A, ‘O’
LCALL DISPLAY Display lettter O
MOV A, ‘M’
LCALL DISPLAY Display lettter M
UNIT-V 5.7
MOV A, ‘E’
LCALL DISPLAY Display lettter E
SJMP Here:Here Look here after displaying message
Command Routine:
LCALL READY Check whether LCD is ready?
MOV P1, A Issue command code
CLR P3.2 Make RS=0 to issue command
CLR P3.3 Make R/ = 0 to enable writing command
SETB P3.4 Make E=1
CLR P3.4 Make E=0
RET Return
READY Routine:
CLR P3.4 Disable display
CLR P3.2 make RS = 0 to access command register
MOV P1, #OFFh configure p1 as an input port
SETB P3.3 Make R/ = 0 to eneble reading
SETB P3.4 Make E = 1
JB P1.7, READ Check DB7 bit. If it is 1, LCD is busy hence check
if until it is 0
CLR P3.4 Make E = 0 to disable display
RET Return
Display Routine:
LCALL READY Check whether LCD is ready?
MOV P1, A Issue data
SETB P3.2 Make RS = 1 to issue data
CLR P3.3 Make R/ = 0 to enable writing
SETB P3.4 Make E = 1
CLR P3.4 Make E = 0
RET Return
UNIT-V 5.8
5.2 DAC Interface
To convert the digital signal to analog signal a Digital-to-Analog Converter (DAC) has to
be employed.
The DAC will accept a digital (binary) input and convert to analog voltage or current.
Every DAC will have “n” input lines and an analog output.
The DAC require a reference analog voltage (Vref) or current (Iref) source.
The smallest possible analog value that can be represented by the n-bit binary code is
called resolution.
The resolution of DAC with n-bit binary input is 1/2nof reference analog value.
Every analog output will be a multiple of the resolution.
For example, consider an 8-bit DAC with reference analog voltage of 5 volts. The analog
values for all possible digital input are as shown.
5.2.1 Pin diagram & block diagram of DAC0800
The DAC0800 is an 8-bit, high speed, current output DAC with a typical settling time
(conversion time) of 100 ns.
It produces complementary current output, which can be converted to voltage by using
simple resistor load.
The DAC0800 require a positive and a negative supply voltage in the range of ± 5V to
±18V.
It can be directly interfaced with TTL, CMOS, PMOS and other logic families.
For TTL input, the threshold pin should be tied to ground (VLC = 0V).
UNIT-V 5.9
The reference voltage and the digital input will decide the analog output current, which
can be converted to a voltage by simply connecting a resistor to output terminal or by
using an op-amp I to V converter.
The DAC0800 is available as a 16-pin IC in DIP.
The pin configuration of DAC0800 is,
Fig 5.3: Pin configuration of DAC0800
The internal block diagram of DACO800 is,
UNIT-V 5.10
Fig 5.4: Block diagram of DAC000
5.2.2 Interfacing DAC0800 with 8031/8051 Microcontroller
In simple systems, when the ports are free the DAC0800 can be directly interfaced to an
8-bit port of any 8x5x family of controller as shown.
Fig 5.5: Interfacing DAC0800 with 8031/8051 Microcontroller
In this system the controller can be programmed to work as signal generator for various
applications and the program can be permanently stored in the internal program memory
of the controller.
Since the 8x5x ports are internally provided with latch there is no need for external latch
to interface DAC0800.
The DAC0800 can also be interfaced to 8031/8051 microcontroller as memory mapped
I/O as,
UNIT-V 5.11
Fig 5.6: DAC memory mapped interface with 8051
In this case an 8-bit latch such as 74LS273 is interfaced to system bus and mapped in the
data memory address space with 16-bit address.
The DAC0800 is connected to output lines of the latch. The controller will load the digital
data to the latch and it will hold the data on its output lines.
The next data will be loaded to latch only when previous data has been converted to
analog value.
The loading of consecutive data to the latch of DAC is controlled by software time delay.
The address lines A13, A14 and A15 are decoded to generate 8 chip select signals and in
this the low signal CS3 is used as logic low enable for the DAC latch 74LS273.
The low signals RD and WR are logically ANDed and used as logic low enable for
decoder and the low signal PSEN is as logic high enable for decoder.
The address allotted to DAC latch is,
UNIT-V 5.12
Program:
MOV SP, #08H
REPEAT: MOV PI, #0FFH
MOV P, #00H
LCALL DELAY
LJMP REPEAT
DELAY: MOV R0, #0FFH
BACK: DJNZ R0, BACK
RET
5.3 Interfacing ADC
5.3.1 ADC 0809
The ADC0809 is an 8-bit successive approximation type ADC with inbuilt 8-channel
multiplexer.
The ADC0809 is suitable for interface with 8086 microprocessor.
The ADC0809 is available as a 28 pin IC in DIP (Dual Inline Package).
The ADC0809 has a total unadjusted error of ±1 LSD (Least Significant Digit).
The ADC0808 is also same as ADC0809 except the error. The total unadjusted error in
ADC0808 is ± 1/2 LSD.
The pin configuration of ADC0809/ADC0808 is,
UNIT-V 5.13
Fig 5.7: Pin configuration or ADC0809
UNIT-V 5.14
The internal block diagram of ADC0809/ADC0808 is,
Fig 5.8: Internal block diagram of ADC0809
The various functional blocks of ADC are 8-channel multiplexer, comparator, 256R
resistor ladder, switch tree, successive approximation register, output buffer, address latch
and decoder.
The 8-channel multiplexer can accept eight analog inputs in the range of 0 to 5V and
allow one by one for conversion depending on the 3-bit address input. The channel
selection logic is,
UNIT-V 5.15
The successive approximation register (SAR) performs eight iterations to determine
the digital code for input value. The SAR is reset on the positive edge of START
pulse and start the conversion process on the falling edge of START pulse.
A conversion process will be interrupted on receipt of new START pulse.
The End-Of-Conversion (EOC) will go low between 0 and 8 clock pulses after the
positive edge of START pulse.
The ADC can be used in continuous conversion mode by tying the EOC output to
START input. In this mode an external START pulse should be applied whenever
power is switched ON.
The 256’R resistor network and the switch tree is shown in fig.
Fig 5.9: 256’R resistor network
The 256R ladder network has been provided instead of conventional R/2R ladder because
of its inherent monotonic, which guarantees no missing digital codes.
Also the 256R resistor network does not cause load variations on the reference voltage.
The comparator in ADC0809/ADC0808 is a chopper- stabilized comparator. It converts
the DC input signal into an AC signal, and amplifies the AC sign using high gain AC
amplifier. Then it converts AC signal to DC signal. This technique limits the drift
component of the amplifier, because the drift is a DC component and it is not
amplified/passed by the AC amp1ifier. This makes the ADC extremely insensitive to
temperature, long term drift and input offset errors.
UNIT-V 5.16
5.3.2 ADC0809 interfacing with 8051
In ADC conversion process the input analog value is quantized and each quantized analog
value will have a unique binary equivalent.
The quantization step in ADC0809/ADC0808 is given by,
Fig 5.10: Interfacing ADC0809 with 8051
AD Conversion Program
MOV P1, #OFFH Configure port1 as input
BACK CLR P2.6 (make = 0 and
SETB P2.6 make = 1 to generate start of conversion
Pulse)
Again JB P2.7, Again Wait for end of conversion
CLR P2.5 Enable read
MOV A, P1 Read data through port1
SETB P2.5 Disable read after reading data
UNIT-V 5.17
SJMP BACK go for next conversion cycle
5.4 Temperature Control
Transducers convert physical data such as temperature, light intensity, flow and speed to
electrical signals.
The output of the temperature sensor is non linear. The complexity associated with
writing soft ware for such non linear devices has led to the manufacturing of linear
temperature sensor.
Example: LM34 and LM35
The transducers produce an output in the form of voltage, current, capacitance and resistance.
Signal conditioning can be current to voltage conversion or signal amplification.RTD is also
called Platinum RTD because it is typically made of platinum. A change in temperature
causes a change in resistance of platinum. This change can be measured with an ohmmeter.
Within a limited range, the resistance of metals increases in proportion to the temperature.
In theory, any metal could be used to measure temperature. The metal selected
should have a high melting point and an ability to withstand the effects of corrosion. Platinum
has therefore become the metal of choice for RTD's. Its desirable characteristics include
chemical stability, availability in a pure form, and electrical properties that are highly
reproducible.
5.4.1 Microprocessor based temperature control system
Fig 5.11: Temperature sensor interface with 8051
UNIT-V 5.18
Fig 5.12: Flowchart of control algorithm
The change of resistance must be translated into voltage in order to use an
ADC. ADC804 has 8bit resolution with a maximum of 256(28) steps and the LM35 produces
10mV for every degree of temperature change, we can condition Vin of the ADC804 to
produce the Vout of 2560 mV for full scale output.
5.5 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 drivers, dot
matrix printers, and robotics, etc.
Every stepper motor has a permanent magnet rotor (also called the shaft) surrounded
by a stator .
5.5.1 Construction
UNIT-V 5.19
Fig 5.13: Construction diagram of stepper motor
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 stepper motor
The center tap allows a change of current direction in each of two coils when a
winding is grounded, thereby resulting in a polarity change of the stator.
Fig 5.14: Stator windings configuration
The stepper motor discussed here has a total of 6 leads, 4 leads representing the four
stator windings, 2 commons for the center tapped leads.
As the sequence of power is applied to each stator winding, the rotor will rotate. The
normal 4 step sequence
UNIT-V 5.20
5.5.2 Interfacing
Fig 5.15: Stepper motor interfacing
The step angle is the minimum degree of rotation associated with a angles for various
motors
The step per revolution is the total number of steps needed to rotate one complete
rotation or 360 degrees.
The relation between RPM (revolutions per minute), steps per revolution, and
steps per second is as follow
Steps/Sec = RPM x Steps per revolution / 60.
After completing every four steps, the rotor moves only one tooth pitch.
The smaller the step angle, the more teeth the motor passes.
Ex: In a stepper motor with 200 steps per revolution, its rotor has 50 teeth since 4 x 50
= 200 steps are needed.
To allow for finer resolutions, all stepper motors allow what is called an 8-step switching
sequence. It’s also called half-stepping, since each step is half of the normal step angle. The
Half step 8 step sequence is as follows
UNIT-V 5.21
5.6 Keyboard Interface
Push button keys are used to interface keyboard to microcontroller
based system. These push button keys when pressed, bounces a few times, closing and
opening the contacts before providing the steady reading.
Fig 5.16: Bouncing of key switch
5.6.1 Key bounce using software
If key press is found the controller wait for 10ms before it accepts the key as an
input. This time period is sufficient to settle the key.
UNIT-V 5.22
Fig 5.17: Flow chart of key input with bounce
5.6.2 Simple keyboard Interface
Fig 5.18: Simple keyboard Interface
Pins of Port1 are connected to keys. When port pin is logic 1, key is open,
otherwise key is closed.
Software routine to get key code with key debounce is as follows
START: MOV A, P1 read key status
Check if keys are open
CJNE A, #FFH, START if no, go to start otherwise continue.
UNIT-V 5.23
PRO: LCALL DEBOUNCE_DELAY call debounce delay
AGAIN: MOV A, P1 read key status
CJNE A, #FFH PRO1 check if any key is pressed
LJMP AGAIN if no go to AGAIN; otherwise continue
PRO1: LCALL DEBOUNCE_DELAY call debounce delay
MOV A, P1 get key code
RET Return from subroutine
The above program read the status of each keys by compare the port pins data with
FFH to check whether all keys are open. After that if all keys are open data is compared with
zero flag and wait for key bounce. After 10ms program check for key press.
5.6.3 Matrix Keyboard interface
Sixteen keys are arranged in 4 rows and 4 columns. When keys are
open no rows and columns are interconnected. When key is pressed it shorts corresponding
rows and columns.
UNIT-V 5.24
Fig 5.19: Matrix keyboard
Fig 5.20: Matrix keyboard interface
Check 1:
Whether any key is pressed or not.
1. Make all column lines zero by sending low on all output lines. This activates all keys
is in the keyboard matrix.
2. Read the status of return lines. If the status of all lines is logic high, key is not
pressed; otherwise key is pressed.
Check 2:
1. Activate keys from any one column by making any one column line zero.
2. Read the status of return lines. The zero on any return line indicates key is pressed
from the corresponding row and selected column. If the status of all lines is logic
high, key is not pressed from that column.
3. Activate the keys from the next column and repeat 2 and 3 for all columns.
UNIT-V 5.25
Fig 5.21: 4X4 matrix keyboard connected to port1 of 8051
The steps in algorithm
1. Initialize P1.0, P1.1, P1.2, and P1.3 as inputs.
2. Check if all keys are released by writing ‘0’ to P1.4-P1.7 and check all return lines are
in state ‘1’.
If yes then go to step 3.
3. Call debounce.
4. Wait for key closure. Ground all scan lines by writing ‘0’ and check if atleast one of
return lines shows ‘0’ level.
Key pressed? No step 4
Yes step 5
5. Call debounce.
6. Is key really pressed? No step 4
Yes step 7
7. Find key code and display the key pressed on 7-segment display.
8. Go to step 1
Program:
Org lookup_table_address
DB, 30h, 31h, 33h, 34h, 35h, 36h, 37h,
38h, 39h, 41h, 42h, 43h, 44h, 45h, 46h
Org program_start_address
UNIT-V 5.26
BEG: MOV A, P1, OFh configure lower 4 lines of port 1 as i/p
MOV DPTR, # lookup_table_address initialize dptr with lookup_table_addr.
AGA: MOV A, P1
ANL A, OFh
CJNE A, #OFh, AGA check for key released
LCALL DELAY call delay routine for key bounce
AGAL: MOV A, P1
ANL A, #OFh
CJNE A, #OFh, GO check for key pressed
LJMP AGAL
GO: LCALL DELAY call delay routine for key bounce
MOV A, P1
ANL A, #OFh
CJNE A, #OFh, GO1 Check whether key is really pressed?
LJMP AGAL
GO1: MOV r1, #01h initialize counter 1
MOV r0, #0EFh store word for column selection
MOV r3, #O4h initialize column counter
AGA3: MOV P1, r0 select only one column
MOV A, P1 get the status of return lines
JNB ACC.0, DISPLAY check bit 0 and if it is 0 jump to display
INC DPTR increment look_table pointer
JNB ACC.1, DISPLAY check bit 1 and if it is 1 jump to display
INC DPTR increment look_table pointer
JNB ACC.2, DISPLAY check bit 2 and if it is 2 jump to display
INC DPTR increment look_table pointer
JNB ACC.3, DISPLAY check bit 3 and if it is 3 jump to display
INC DPTR increment look_table pointer
MOV A,r0 get the word for column selecion
R1 A select next column
MOV r0, A store word for column selection
DJNZ r3, AGA3 check for last column
LJMP BEG if key any is not pressed scan again
END
UNIT-V 5.27
5.7 Motor Speed Control System
5.7.1 DC motor (or) Direct Current motor
It is a device which is used to translate electrical pulses into mechanical movement .It has
two terminals ‘+’ & ’-‘. If DC voltage is applied between these2 terminals then the motor is
rotated in one direction, if the terminals are reversed, then the motor is rotated in opposite
direction.
5.7.2 DC motor speed control
If the load is increased, then the rpm is decreased. If the motor is overloaded, then it will be
damaged due to the generation of heat.
1. Unidirectional control - DC motor is rotated in clock wise direction or in counter
clockwise direction.
2. Bidirectional control - By using relay, we can change the direction of the rotation of
the DC motor.
5.7.3 Pulse Width Modulation (PWM)
If the load is fixed, then we can maintain a steady speed by using pulse width by modulation
method .The speed of the motor can be increased or decreased by changing the width of the
pulse applied to the motor. This technique is mostly used in DC motor control.PWM circuit is
embedded in some microcontrollers.
5.7.4 DC motor control using L293
The interfacing circuit DC motor with 8051. Already we had seen the H-bridge
configuration. Here, diode is used as a switch .Bidirectional control is achieved by using by
above circuit .In 8051,we can write the program for motor control .Port 1 is used for
interfacing.
Fig 5.22: DC motor control using L293
5.7.5 DC motor control using Optoisolator
UNIT-V 5.28
Opto isolator is used for motor control. The capacitor C is connected across
DC motor. It is used to reduce the EMI produced by the motor. The collector of the transistor
is connected with the motor. Opto isolator is used for the protection purpose.
Fig 5.23: DC motor control using Optocoupler
PART A
1. What is resolution in DAC?
2. What are the internal devices of a typical DAC?
3. What is settling or conversion time in DAC?
4. What are the different types of DAC?
5. What are the different types of ADC?
6. What is resolution in ADC?
7. What is conversion time in ADC?
8. What is the function of DAC?
9. List the advantages of using LCD in the place of LEDs.
UNIT-V 5.29
10. What is the function of temperature sensor?
11. What is the operation of stepper motor?
12. Explain the DC motor speed control using 8051.
13. What is the function of keyboard & display unit?
PART B
1. Explain the Keyboard and display interface with 8051. Show the interfacing for a 4 X 4
keyboard matrix.
2. Explain the stepper motor control using 8051.
3. Explain the DC motor speed control using 8051.
4. Explain DAC and its interfacing with 8051.
5. Explain ADC and its interfacing with 8051.
6. Explain LCD and its interfacing with 8051.
7. Explain in detail the interfacing of temperature sensor with 8051.
