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MICROCONTROLLER
A microcontroller is a small computer on a single integrated circuit containing a processor
core, memory, and programmable input/output peripherals. Program memory in the form of
NOR flash or OTP ROM is also often included on chip, as well as a typically small amount
of RAM. Microcontrollers are designed for embedded applications, in contrast to the
microprocessors used in personal computers or other general purpose applications.
Microcontrollers are used in automatically controlled products and devices, such as
automobile engine control systems, implantable medical devices, remote controls, office
machines, appliances, power tools, toys and other embedded systems. By reducing the size
and cost compared to a design that uses a separate microprocessor, memory, and input/output
devices, microcontrollers make it economical to digitally control even more devices and
processes. Mixed signal microcontrollers are common, integrating analog components needed
to control non-digital electronic systems.
Some microcontrollers may use four-bit words and operate at clock rate frequencies as low as
4 kHz, for low power consumption (milli watts or microwatts). They will generally have the
ability to retain functionality while waiting for an event such as a button press or other
interrupt; power consumption while sleeping (CPU clock and most peripherals off) may be
just nanowatts, making many of them well suited for long lasting battery applications. Other
microcontrollers may serve performance-critical roles, where they may need to act more like
a digital signal processor (DSP), with higher clock speeds and power consumption
A microcontroller can be considered a self-contained system with a processor, memory and
peripherals and can be used as an embedded system. The majority of microcontrollers in use
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today are embedded in other machinery, such as automobiles, telephones, appliances, and
peripherals for computer systems. These are called embedded systems. While some
embedded systems are very sophisticated, many have minimal requirements for memory and
program length, with no operating system, and low software complexity.
Typical input and output devices include switches, relays, solenoids, LEDs, small or custom
LCD displays, radio frequency devices, and sensors for data such as temperature, humidity,
light level etc. Embedded systems usually have no keyboard, screen, disks, printers, or other
recognizable I/O devices of a personal computer, and may lack human interaction devices of
any kind.
MICROCONTROLLER FEATURES:
1. (It is similar to 8051 microcontroller i.e. having same instruction set, pin
configuration, architecture).
2. It is also 8-bit microcontroller. Its cost is only Rs10 more than that of 8051.
3. It uses EPROM (erasable programmable read only memory) or FLASH memory.
4. It is multiple time programmable (MTP).
The AT89C51 is a low-power, high-performance CMOS 8-bit microcomputer with 4K
bytes of Flash programmable and erasable read only memory (PEROM). The device is
manufactured using Atmel’s high-density nonvolatile memory technology and is compatible
with the industry-standard MCS-51 instruction set and pinout. 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 chip, the Atmel
AT89C51 is a powerful microcomputer which provides a highly-flexible and cost-effective
solution to many embedded control applications.
The AT89C51 provides the following standard features: 4K bytes of Flash, 128 bytes of
RAM, 32 I/O lines, two 16-bit timer/counters, a five vector two-level interrupt architecture, a
full duplex serial port, on-chip oscillator and clock circuitry. In addition, the AT89C51 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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How to make a digital speedometer using microcontroller
The 8051 may not be the best for this task, in that you can get types with lower power and
small size (8/16 pin dip etc). That is not the only family, but it is popular with hobbyists so
there are plenty of software examples on the internet. You can use this software as an
example for other microprocessors too. The first decision is selecting a display that suits your
microprocessor and hardware.
The most basic concept is a frequency counter. Use a magnetic pickup from the wheel. This
can be mounted on a spoke. You can use a fixed coil of wire or a hall effect device to detect
the magnet. This can be mounted on a wheel fork, so the spoke passes close by. The coil
voltage will need signal processing, like voltage limiting, an op-amp and filter, to convert to
digital pulses for the Processor input.
You could use an optical method instead, using LED and reflection from spokes.
Count the pulses, it is best to measure period between pulses to avoid having to count for n
seconds to get a meaningful result. A problem to overcome is converting this to speed, as you
will have to implement maths (multiply and divide), or use a lookup table. Use a high level
language like C or basic and you have maths easily. The driving of an LCD display depends
on which type you have. You could look that up on the internet.
For odometer, just count the impulses and totalize them, then multiply by the factor to get
miles, km etc. You may want to add some sort of push button to the I/O to control the
display.
The power supply may be a battery, if the microprocessor uses little power, or if you use the
bike power (whatever it is) it will need attention to protect everything from spikes in voltage.
Good filtering before any regulator.
A pic micro is the way to go. Check out www.microchip.com You should find some ideas
and details in their applications section, and you can even procure a free sample or two of
their controllers on their website.
An easy way of counting the pulses from the wheel that will not affect tire balance might be
to use a photo sensor. A simple infrared led and photo transistor, and you won't need much
circuitry to condition the pulse back to the micro controller.
Depending on the color and reflectivity of your tires rim, you would either attach a small
section of flat black tape or a section of reflective tape to the rim in one spot. The photo
sensor could be set up to either count a pulse of reflected light as a signal or the absence of a
light signal as the count.
Basically count the revolutions of the wheel, calculate the wheel's effective circumference,
and you can compute the distance traveled per pulse. Using the micro controllers oscillator as
a time base, you can calculate the number of pulses per unit of time, and using the distance
traveled per pulse, figure out the speed.
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LCD interfacing with Microcontrollers tutorial
►Introduction
The most commonly used Character based LCDs are based on Hitachi's HD44780 controller
or other which are compatible with HD44580. In this tutorial, we will discuss about character
based LCDs, their interfacing with various microcontrollers, various interfaces (8-bit/4-bit),
programming, special stuff and tricks you can do with these simple looking LCDs which can
give a new look to your application.
►Pin Description
The most commonly used LCDs found in the market today are 1 Line, 2 Line or 4 Line LCDs
which have only 1 controller and support at most of 80 charachers, whereas LCDs supporting
more than 80 characters make use of 2 HD44780 controllers.
Most LCDs with 1 controller has 14 Pins and LCDs with 2 controller has 16 Pins (two pins
are extra in both for back-light LED connections). Pin description is shown in the table
below.
Figure 1: Character LCD type HD44780 Pin diagram
Pin No. Name Description
Pin no. 1 VSS Power supply (GND)
Pin no. 2 VCC Power supply (+5V)
Pin no. 3 VEE Contrast adjust
0=Instruction input
Pin no. 4 RS
1 = Data input
0 = Write to LCD module
Pin no. 5 R/W 1 = Read from LCD
module
Pin no. 6 EN Enable signal
Pin no. 7 D0 Data bus line 0 (LSB)
Pin no. 8 D1 Data bus line 1
Pin no. 9 D2 Data bus line 2
Pin no. 10 D3 Data bus line 3
Pin no. 11 D4 Data bus line 4
Pin no. 12 D5 Data bus line 5
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Pin no. 13 D6 Data bus line 6
Pin no. 14 D7 Data bus line 7 (MSB)
Table 1: Character LCD pins with 1 Controller
Pin No. Name Description
Pin no. 1 D7 Data bus line 7 (MSB)
Pin no. 2 D6 Data bus line 6
Pin no. 3 D5 Data bus line 5
Pin no. 4 D4 Data bus line 4
Pin no. 5 D3 Data bus line 3
Pin no. 6 D2 Data bus line 2
Pin no. 7 D1 Data bus line 1
Pin no. 8 D0 Data bus line 0 (LSB)
Pin no. 9 EN1 Enable signal for row 0 and 1 (1stcontroller)
0 = Write to LCD module
Pin no. 10 R/W
1 = Read from LCD module
0 = Instruction input
Pin no. 11 RS
1 = Data input
Pin no. 12 VEE Contrast adjust
Pin no. 13 VSS Power supply (GND)
Pin no. 14 VCC Power supply (+5V)
Pin no. 15 EN2 Enable signal for row 2 and 3 (2ndcontroller)
Pin no. 16 NC Not Connected
Table 2: Character LCD pins with 2 Controller
Usually these days you will find single controller LCD modules are used more in the
market. So in the tutorial we will discuss more about the single controller LCD, the operation
and everything else is same for the double controller too. Lets take a look at the basic
information which is there in every LCD.
►Sending Data to LCD
To send data we simply need to select the data register. Everything is same as the command
routine. Following are the steps:
 Move data to LCD port
 select data register
 select write operation
 send enable signal
 wait for LCD to process the data
Keeping these steps in mind we can write LCD command routine as.
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CODE:
;Ports used are same as the previous example
;Routine to send data (single character) to LCD
LCD_senddata:
mov LCD_data,A ;Move the command to LCD port
setb LCD_rs ;Selected data register
clr LCD_rw ;We are writing
setb LCD_en ;Enable H->L
clr LCD_en
acall LCD_busy ;Wait for LCD to process the data
ret ;Return from busy routine
; Usage of the above routine
; A will carry the character to display on LCD
; e.g. we want to print A on LCD
;
; mov a,#'A' ;Ascii value of 'A' will be loaded in accumulator
; acall LCD_senddata ;Send data
The equivalent C code Keil C compiler. Similar code can be written for SDCC.
CODE:
void LCD_senddata(unsigned char var)
{
LCD_data = var; //Function set: 2 Line, 8-bit, 5x7 dots
LCD_rs = 1; //Selected data register
LCD_rw = 0; //We are writing
LCD_en = 1; //Enable H->L
LCD_en = 0;
LCD_busy(); //Wait for LCD to process the command
}
// Using the above function is really simple
// we will pass the character to display as argument to function
// e.g.
//
// LCD_senddata('A');
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Inductive Proximity Sensor
Inductive Proximity Sensors
Inductive proximity sensors operate under the electrical principle of inductance.
Inductance is the phenomenon where a fluctuating current, which by definition has a
magnetic component, induces an electromotive force (emf) in a target object. To amplify a
device’s inductance effect, a sensor manufacturer twists wire into a tight coil and runs a
current through it. An inductive proximity sensor has four components; The coil, oscillator,
detection circuit and output circuit.
The oscillator generates a fluctuating magnetic field the shape of a doughnut around
the winding of the coil that locates in the device’s sensing face. When a metal object moves
into the inductive proximity sensor’s field of detection, Eddy circuits build up in the metallic
object, magnetically push back, and finally reduce the Inductive sensor’s own oscillation
field. The sensor’s detection circuit monitors the oscillator’s strength and triggers an output
from the output circuitry when the oscillator becomes reduced to a sufficient level.
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Interfacing of 8051 micro controller with Stepper motor
A Unipolar Stepper Motor is rotated by energizing the stator coils in a sequence. In unipolar
stepper, the direction of current in stator coils is not required to be controlled by the driving
circuit. Just applying the voltage signals across the motor coils or motor leads in a sequence
is sufficient to drive the motor.
A two phase unipolar stepper motor has a total of six wires/leads of which four are end wires
(connected to coils) and two are common wires. The color of common wires in the stepper
motor used here is Green. Each common wire is connected to two end leads thus forming two
phases. The end leads corresponding to each phase have to be identified.
In some cases, when the leads cannot be directly identified in the motor, the identification of
endpoints and common points can be done by measuring the resistance between the leads.
The leads of different phase will show open circuited condition with respect to each other.
This way the leads corresponding to different phase can be separated. The resistance between
any two end points of same phase will be twice the resistance between a common point and
an end point. This way the common and end points of both the phases can be identified.
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To work with the unipolar stepper motor, the common points are connected to either Ground
or Vcc and the end points of both the phases are usually connected through the port pins of
a microcontroller. In present case the common (Green) wires are connected to Vcc. The end
points receive the control signals as per the controller's output in a particular sequence to
drive the motor.
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Source code
MAIN.SRC
#include <test_header.h>
ORG 0000H
LJMP MAIN
STR1: DB "COUNTER =$"
STR2: DB "DISTANCE=$"
MAIN:
LCALL INIT_RVCARD
LCALL LCD_INIT
MOV A,#00H
MOV DPTR,#STR1
LCALL LCD_PUTS_LINE1
MOV DPTR,#STR2
LCALL LCD_PUTS_LINE2
SENSOR_RELAY11:
; this is to demonostrate the use of SENSOR and RELAY
; P1.7 -- connected to Relay input
; P3.7 -- connected to Opto Isolator input i.e sensor input
; this program reads from the sensor and controls ac device connected to relay
; continuously and it is of indefinite loop
AAGAIN:JB P3.7,AAGAIN
/*MOV A,#25H
MOV B,#65H
MUL AB
MOV P0,B
LCALL DELAY
MOV P0,A*/
REL_ON1:
MOV P0,#0FFH
ADD A,#01
MOV R3,A
PUSH 0E0H
LCALL BINARY_TO_HEX
MOV A,#8DH
LCALL LCD_CWRITE
MOV A,R2
LCALL LCD_DWRITE
MOV A,R1
LCALL LCD_DWRITE
MOV A,R0
LCALL LCD_DWRITE
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MOV A,#02 //2*3.142*r(radius)*f(rotations per second)
MOV B,#01 //B contains radius 1 cm
MUL AB
MOV R4,A
MOV A,#03// ASSUMING PI VALUE AS 3
MOV B,R3 //NO OF ROTATIONS PER SECOND
MUL AB
MOV B,R4
MUL AB
LCALL BINARY_TO_HEX
MOV A,#8DH
ADD A,#40H
LCALL LCD_CWRITE
MOV A,R2
LCALL LCD_DWRITE
MOV A,R1
LCALL LCD_DWRITE
MOV A,R0
LCALL LCD_DWRITE
POP 0E0H
//LCALL DISP_DIST
AGAIN1: JNB P3.7,AGAIN1
SJMP SENSOR_RELAY11
SJMP $
END
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STEPPER.SRC
#include <test_header.h>
ORG 0000H
LJMP AA
STR1: DB "STEPPER MOTOR$"
AA: LCALL INIT_RVCARD
LCALL LCD_INIT
MOV DPTR,#STR1
LCALL LCD_PUTS_LINE1
STEP: MOV A,#88H
MOV R0,#100 ;100 steps in the clockwise direction
CONT:
MOV P0,A
LCALL DELAYMS
LCALL DELAYMS
RR A ;rotate the pattern in clockwise direction
//LCALL SENSOR_RELAY11
DJNZ R0,CONT
SJMP STEP
//LCALL SENSOR_RELAY11*/
/
SJMP $
END
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