AUTOMATIC CAR PARKING SYSTEM USING 89C51

MICROCONTROLLER

The Project Automatic Car Parking System using 89C51 Microcontroller is an

interesting project which uses 89C51 microcontroller as its brain. The project is designed

for car parking.

The aim of this project is to atomize the car park for allowing the cars into the

park. LCD is provided to display the information about the total number of cars that can

be parked and the place free for parking. Two IR TX – RX pairs are used in this project

to identify the entry or exit of the cars into/out of park. These two IR TX – RX pairs are

arranged either side of the gate. The TX and RX are arranged face to face across the road

so that the RX should get IR signal continuously.

Whenever the mains are switched on, the LCD displays the message “parking

space for 10 vehicles”. The number indicates the maximum capacity of park in this

project. Whenever a car comes in front of the gate, the IR signal gets disturbed and the

microcontroller will open the gate by rotating the stepper motor. The gate will be closed

only after the car leaves the second IR pair since the microcontroller should know

whether the car left the gate or not. Now the microcontroller decrements the value of the

count and displays it on LCD. In this way, the microcontroller decrements the count

whenever the car leaves the park and displays it on LCD.

If the count reaches ‘0’, i.e. if the park is completely filled, the microcontroller

will display “NO SPACE FOR PARKING” on LCD. And now if any vehicle tries to

enter the park, the gate will not be opened since there is no space. If any vehicle leaves

the park, the controller will increment the count and allows the other vehicles for parking.

This project uses regulated 5V, 500mA power supply. Unregulated 12V DC is

used for relay. 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.

Figure:1.1 Block Diagram: Automatic Car Parking System using 89C51 Microcontroller

EXIT SENSOR IR

89C51

STEPPER MOTOR 1

ULN 2003

Power supply to all sections

Step down T/F

Bridge Rectifier

Filter Circuit Regulator

CRYSTAL

RESETCIRCUIT

STEPPER MOTOR 1

ENTRY SENSOR IR

DESCRIPTION

POWER SUPPLY:

The 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.

Figure 2.1: Power supply

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

RegulatorFilter

Bridge

Rectifier

Step down

transformer

230V AC 50Hz D.C

Output

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.

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.

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.

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.

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 a Harvard architecture, single chip microcontroller (µC) 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 AT89C51. Atmel Corporation

introduced this 89C51 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. AT89C51 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.

FEATURES OF AT89C51:

4K Bytes of Re-programmable Flash Memory.

RAM is 128 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.

Description:

The AT89C51 is a low-voltage, high-performance CMOS 8-bit microcomputer

with 4K bytes of Flash programmable memory. The device is manufactured using

Atmel’s 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 AT89C51 is a powerful microcomputer, which provides

a highly flexible and cost-effective solution to many embedded control applications.

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.

Figure2.2: Pin diagram

PIN 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.

Table: Port 3 Alternate Functions

Machine 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.

SOFTWARES USED:

KEIL COMPILER:

Keil compiler is a 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.

PROLOAD:

Proload is a 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.

IR SECTION:

WHAT IS INFRARED?

Infrared is a energy radiation with a frequency below our eyes sensitivity, so we cannot

seeit

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.

 INFRARED IN ELECTRONICS

Infra-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, 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 36kHz

IR GENERATION

To generate a 36kHz 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.

Figure :2.3 IR generation

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

commercial receiver 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 50kHz.  So, all of them use a different combination of

bits or how to code the transmitted data to avoid interference. 

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).

IR RECEIVER

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.

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

figure :2.5 IR RECEIVER

figure :3.3

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 fullfill the following condition: • Carrier frequency should

be close to center frequency of the bandpass (e.g. 38kHz).

• 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, R–2000 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).

figure :3.4

ULN2003 CURRENT DRIVER:

Fig: DIP 16 Package

The 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.

Fig: Pin Connection

This 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.

One of the coil terminals of the relay will be connected to the output pin of the ULN

driver. Thus in order to switch on the relay to operate any load, the output from the ULN

driver (any one of the 7 outputs) should be low. Thus for the output to be low, the input

applied at that corresponding input pin should be high. The input to the ULN driver is

provided by the microcontroller. Thus the instruction required to operate the relay

through the microcontroller is

SETB PX.Y

Where X is the port number (P0, P1, P2 and P3)

And Y is the pin number of Port X.

RELAY INTERFACING WITH THE MICROCONTROLLER:

Figure :4.4

1 U 16 2 L 153 N 144 2 135 0 126 0 117 3 108 9

RELAY LOAD

GroundVcc

AT 89C51

P1.0

STEPPER MOTOR:

Figure 5.1: 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.

Figure 5.2 : Stepper motor operation

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.

Disadvantages:

1. Resonances can occur if not properly controlled.

2. Not easy to operate at extremely high speeds.

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.

Stepper Motor Types:

There are three basic stepper motor types. They are :

• Variable-reluctance

• Permanent-magnet

• Hybrid

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.

Figure 5.3: Cross-section of a variable reluctance (VR) motor.

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.

PM stepper motor principle Cross section of a hybrid stepper motor

Figure : 5.4

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.

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.

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.

Figure :5.5: Magnetic flux path through a two-pole stepper motor with a lag

between the rotor and stator.

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

where

N = 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.

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.

Figure 6.1: Positional accuracy of a stepper motor

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.

Figure6.2: Torque versus speed characteristics

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 phenomena 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.

Figure6.3: Single step response versus time

Few 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 angle Steps per Revolution

0.72 500

1.8 200

2.0 180

2.5 144

5.0 72

7.5 48

15 24

Fig: Stepper motor step angles

2. 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.

Figure 6.4:STEPPER MOTOR INTERFACING WITH MICROCONTROLLER:

1 U 16 2 L 153 N 144 2 135 0 126 0 117 3 108 9

STEPPER MOTOR

GroundVcc

AT 89C51

P1.0 P1.1 P1.2 P1.3

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.

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.

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:

FunctionPin

NumberName

Logic State

Description

Ground 1 Vss - 0V

Power supply 2 Vdd - +5V

Contrast 3 Vee - 0 - Vdd

Control of operating

4 RS01

D0 – D7 are interpreted as commands

D0 – D7 are interpreted as data

5 R/W01

Write data (from controller to LCD)

Read data (from LCD to controller)

6 E

01

From 1 to 0

Access to LCD disabledNormal operating

Data/commands are transferred to LCD

Data / commands

7 D0 0/1 Bit 0 LSB

8 D1 0/1 Bit 1

9 D2 0/1 Bit 2

10 D3 0/1 Bit 3

11 D4 0/1 Bit 4

12 D5 0/1 Bit 5

13 D6 0/1 Bit 6

14 D7 0/1 Bit 7 MSB

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).

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:

Command RS RW D7 D6 D5 D4 D3 D2 D1 D0Execution

Time

Clear display 0 0 0 0 0 0 0 0 0 1 1.64mS

Cursor home 0 0 0 0 0 0 0 0 1 x 1.64mS

Entry mode set 0 0 0 0 0 0 0 1 I/D S 40uS

Display on/off control 0 0 0 0 0 0 1 D U B 40uS

Cursor/Display Shift 0 0 0 0 0 1 D/C R/L x x 40uS

Function set 0 0 0 0 1 DL N F x x 40uS

Set CGRAM address 0 0 0 1 CGRAM address 40uS

Set DDRAM address 0 0 1 DDRAM address 40uS

Read “BUSY” flag (BF) 0 1 BF DDRAM address -

Write to CGRAM or DDRAM

1 0 D7 D6 D5 D4 D3 D2 D1 D0 40uS

Read from CGRAM or DDRAM

1 1 D7 D6 D5 D4 D3 D2 D1 D0 40uS

I/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 dots

B 1 = Cursor blink on D/C 1 = Display shift

0 = Cursor blink off 0 = Cursor shift

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.

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.

Figure : Procedure on 8-bit initialization.

CONTRAST CONTROL:

To have a clear view of the characters on the LCD, contrast should be adjusted. To adjust

the contrast, the voltage should be varied. For this, a preset is used which can behave like

a variable voltage device. As the voltage of this preset is varied, the contrast of the LCD

can be adjusted.

Figure 7.1: Variable resistor

Potentiometer

Variable resistors used as potentiometers have all three terminals connected.

This arrangement is normally used to vary voltage, for example to set the switching

point of a circuit with a sensor, or control the volume (loudness) in an amplifier circuit. If

the terminals at the ends of the track are connected across the power supply, then the

wiper terminal will provide a voltage which can be varied from zero up to the maximum

of the supply.

Presets

Potentiometer Symbol 

These are miniature versions of the standard variable resistor. They are designed to be

mounted directly onto the circuit board and adjusted only when the circuit is built. For

example to set the frequency of an alarm tone or the sensitivity of a light-sensitive circuit.

A small screwdriver or similar tool is required to adjust presets.

Presets are much cheaper than standard variable resistors so they are sometimes used in

projects where a standard variable resistor would normally be used.

Multiturn presets are used where very precise adjustments must be made. The screw

must be turned many times (10+) to move the slider from one end of the track to the

other, giving very fine control.

Preset Symbol 

LCD INTERFACING WITH THE MICROCONTROLLER:

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.

Light-emitting diodes are elements for light signalization in electronics. They are

manufactured in different shapes, colors and sizes. For their low price, low consumption

and simple use, they have almost completely pushed aside other light sources- bulbs at

first place. They perform similar to common diodes with the difference that they emit

light when current flows through them.

It is important to know that each diode will be immediately destroyed unless its current is

limited. This means that a conductor

must be connected in parallel to a

diode. In order to correctly determine

value of this conductor, it is necessary

to know diode’s voltage drop in

forward direction, which depends on

what material a diode is made of and

what colour it is. Values typical for the

most frequently used diodes are shown

in table below: As seen, there are three main types of LEDs. Standard ones get ful

brightness at current of 20mA. Low Current diodes get ful brightness at ten times lower

current while Super Bright diodes produce more intensive light than Standard ones.

Since the 8051 microcontrollers can provide only low input current and since their pins

are configured as outputs when voltage level on them is equal to 0, direct connectining to

LEDs is carried out as it is shown on figure (Low current LED, cathode is connected to

output pin).

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.

Figure7.2: LED Interfacing with the microcontroller

In this project, four LEDS are used, two for each IR section. Red LED is to indicate that

the gate is closed and Green LED to indicate the gate is opened.

P1.0

Vcc

Figure 7.3: Schematic diagram

WORKING PROCEDURE:

Automatic car parking system using 89C51 microcontroller is an exclusive project

which allows the cars to be parked in cellars based on the availability without the

involvement of a human. In this project, two pairs of IR Transmitters and Receivers are

used. One pair is placed at the entry gate and the other is placed at the gate used for

leaving the cellar.

Initially the information regarding the space for the vehicles will be displayed on

LCD (Liquid Crystal Display). The operation of this system starts when a vehicle tries to

park in the cellar. The IR pair placed at this gate detects the vehicle arriving at the entry

gate as the vehicle will be interrupting the IR signal falling on to the IR receiver from the

transmitter. Then the gate will be opened as this action is preprogrammed in the

microcontroller and automatically the count will be decremented for allowing the

vehicles to enter. This project provides space for a maximum of 4 vehicles to be parked.

The opening and closing of the gate is controlled by the stepper motor. This gate remains

open for some time allowing the vehicle to enter there and then closes automatically. The

information about the space for the other vehicles will be continuously displayed on the

LCD for the easy check of the other vehicles to enter into.

Now the second IR pair starts working, i.e., when a vehicle wants to leave the

place, the vehicle will be waiting at the exit gate then the vehicle will be interrupting the

IR signal falling on to the IR receiver from the transmitter. Now the gate which is used

for leaving the place opens and will remain open for some time allowing the vehicle to

leave and the closes again and gets locked and the information will be updated on the

LCD whenever a vehicle exits out from the cellar.

The operation continues upto 10 vehicles if no vehicle left the cellar. i.e., the

LCD display will be now “NO SPACE FOR NEW VEHICLES” unless a vehicle exits

out. Thus, this system will not allow another vehicle when there is no space in the cellar

completely avoiding the man involvement and automising the control to allow the

vehicles to be parked.

;***********SOURCE CODE****************************************

;*************** CAR PARKING SYSTEM *****************

;*************** WK-212 *****************

;********************************************************

; P3.6 AND P3.7 RECEIVERS OF ENTRY AND EXIT SENSORS RESP.

; P1.0,P1.1,P1.2 AND P1.3 STEPPER MOTOR A,B,C AND D COILS

; P2 LCD DATA PINS

; P3.0,P3.1 AND P3.2 ARE RS,R/W AND EN PINS OF LCD RESP.

ORG 00H

SETB P3.6 ; MAKING P3.6 AS I/P PIN

SETB P3.7 ; MAKING P3.7 AS I/P PIN

MOV R6,#10 ; VEHICLE CAPACITY OF PARK

;******* LCD INITIALISATION ****************************

MOV DPTR,#COMM

BACK1 : CLR A

MOVC A,@A+DPTR

JZ NEXT

ACALL COMN

ACALL DELAY

INC DPTR

SJMP BACK1

;****** LCD INITIAL MESSAGE DISPLAY ********************

NEXT : MOV DPTR,#MESG4

ACALL BACK2

ACALL DELAY1

MOV A,#0C0H

ACALL COMN

ACALL DELAY

MOV DPTR,#MESG5

ACALL BACK2

ACALL FORDELAY

ACALL FORDELAY

MOV A,#01H

ACALL COMN

ACALL DELAY

MOV A,#82H

ACALL COMN

ACALL DELAY

MOV DPTR,#MESG6

ACALL BACK2

MOV A,#0C5H

ACALL COMN

ACALL DELAY

MOV DPTR,#MESG7

ACALL BACK2

ACALL FORDELAY

ACALL FORDELAY

MOV A,#01H

ACALL COMN

ACALL DELAY

MOV A,#81H

ACALL COMN

ACALL DELAY

MOV DPTR,#MESG

ACALL BACK2

MOV A,#0C0H

ACALL COMN

ACALL DELAY

MOV DPTR,#MESG1

ACALL BACK2

MOV A,#0C4H

ACALL COMN

ACALL DELAY

MOV A,#'1'

ACALL DATAWRT

ACALL DELAY

MOV A,#'0'

ACALL DATAWRT

ACALL DELAY

;*********** CHECKING FOR VEHICLE ENTRY OR EXIT ********

BACK : JNB P3.6,ENTRY

JNB P3.7,EXIT

SJMP BACK

;*********** OPENING THE GATE FOR VEHICLE ENTRY ********

ENTRY : MOV R7,#10

MOV A,#66

ACALL RUNACW

DEC R6

MOV A,#0C4H

ACALL COMN

ACALL DELAY

MOV A,R6 ; DISPLAYING CURRENT CAPACITY

ANL A,#0F0H

ORL A,#30H

ACALL DATAWRT

ACALL DELAY

MOV A,#0C5H

ACALL COMN

ACALL DELAY

MOV A,R6

ANL A,#0FH

ORL A,#30H

ACALL DATAWRT

ACALL DELAY1

STAY : JNB P3.6,STAY

ACALL DELAY1

ACALL DELAY1

STAY1 : JB P3.7,STAY1 ; FOR EXIT GATE HIGH TO LOW

STAY2 : JNB P3.7,STAY2

ACALL FORDELAY

MOV R7,#10

MOV A,#66

ACALL RUNCW

CJNE R6,#00,BACK

MOV A,#01

ACALL COMN

ACALL DELAY

MOV A,#82H

ACALL COMN

ACALL DELAY

MOV DPTR,#MESG2

ACALL BACK2

MOV A,#0C4H

ACALL COMN

ACALL DELAY

MOV DPTR,#MESG3

ACALL BACK2

STAY4EXIT : JB P3.7,STAY4EXIT ; WAITING FOR EXIT OF

VEHICLE

MOV A,#01

ACALL COMN

ACALL DELAY

MOV A,#81H

ACALL COMN

ACALL DELAY

MOV DPTR,#MESG

ACALL BACK2

MOV A,#0C0H

ACALL COMN

ACALL DELAY

MOV DPTR,#MESG1

ACALL BACK2

ACALL DELAY

EXIT : MOV R7,#10

MOV A,#66

ACALL RUNACW

INC R6

MOV A,#0C4H

ACALL COMN

ACALL DELAY

MOV A,R6

MOV B,#10

DIV AB

ORL A,#30H

ACALL DATAWRT

ACALL DELAY

MOV A,#0C5H

ACALL COMN

ACALL DELAY

MOV A,B

ORL A,#30H

ACALL DATAWRT

STAY3 : JNB P3.7,STAY3

ACALL DELAY1

STAY4 : JB P3.6,STAY4

STAY5 : JNB P3.6,STAY5

ACALL FORDELAY

MOV R7,#10

MOV A,#66

ACALL RUNCW

LJMP BACK

FORDELAY:ACALL DELAY2

ACALL DELAY2

ACALL DELAY2

ACALL DELAY2

ACALL DELAY2

ACALL DELAY2

ACALL DELAY2

ACALL DELAY2

ACALL DELAY2

ACALL DELAY2

ACALL DELAY2

RET

RUNACW: CLR P1.0

SETB P1.1

SETB P1.2

CLR P1.3

ACALL DELAY1

CLR P3.0

SETB P3.1

SETB P3.2

CLR P3.3

ACALL DELAY1

SETB P1.0

SETB P1.1

CLR P1.2

CLR P1.3

ACALL DELAY1

SETB P3.0

SETB P3.1

CLR P3.2

CLR P3.3

ACALL DELAY1

SETB P1.0

CLR P1.1

CLR P1.2

SETB P1.3

ACALL DELAY1

SETB P3.0

CLR P3.1

CLR P3.2

SETB P3.3

ACALL DELAY1

CLR P1.0

CLR P1.1

SETB P1.2

SETB P1.3

ACALL DELAY1

CLR P3.0

CLR P3.1

SETB P3.2

SETB P3.3

ACALL DELAY1

DJNZ R7,RUNACW

RET

RUNCW: CLR P1.0

SETB P1.1

SETB P1.2

CLR P1.3

ACALL DELAY1

CLR P3.0

SETB P3.1

SETB P3.2

CLR P3.3

ACALL DELAY1

CLR P1.0

CLR P1.1

SETB P1.2

SETB P1.3

ACALL DELAY1

CLR P3.0

CLR P3.1

SETB P3.2

SETB P3.3

ACALL DELAY1

SETB P1.0

CLR P1.1

CLR P1.2

SETB P1.3

ACALL DELAY1

SETB P3.0

CLR P3.1

CLR P3.2

SETB P3.3

ACALL DELAY1

SETB P1.0

SETB P1.1

CLR P1.2

CLR P1.3

ACALL DELAY1

SETB P3.0

SETB P3.1

CLR P3.2

CLR P3.3

ACALL DELAY1

; MOV P1,A

; RR A

; ACALL DELAY1

DJNZ R7,RUNCW

RET

COMN : MOV P2,A

CLR P1.7

CLR P1.6

SETB P1.5

ACALL DELAY

CLR P1.5

RET

DATAWRT:MOV P2,A

SETB P1.7

CLR P1.6

SETB P1.5

ACALL DELAY

CLR P1.5

RET

BACK2 : CLR A

MOVC A,@A+DPTR

JZ NEXT1

ACALL DATAWRT

ACALL DELAY

INC DPTR

SJMP BACK2

NEXT1 : RET

DELAY : MOV R2,#20

HERE1 : MOV R3,#255

HERE2 : DJNZ R3,HERE2

DJNZ R2,HERE1

RET

DELAY1: MOV R2,#40

HERE3 : MOV R3,#255

HERE4 : DJNZ R3,HERE4

DJNZ R2,HERE3

RET

DELAY2: MOV R2,#255

HERE5 : MOV R3,#255

HERE6 : DJNZ R3,HERE6

DJNZ R2,HERE5

RET

COMM : DB 38H,0CH,01,06,84H,00

MESG4 : DB "WIN KIT",0

MESG5 : DB "LEARNING IS FUN",0

MESG6 : DB "CAR PARKING",0

MESG7 : DB "SYSTEM",0

MESG : DB "PARKING SPACE",0

MESG1 : DB "FOR VEHICLES",0

MESG2 : DB "NO SPACE FOR",0

MESG3 : DB "PARKING",0

END