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Introduction

In todays scenario there is no way to see the inputs that are given to

the microcontroller. This created a problem for the user to see and to checkwhether the input given is correct or not. To avoid such a problem we made

Keypad And LCD Interfacing Using Microcontroller . Thisapplication provides a display for the input that are given to microcontroller

through keypad, by the user.

This project display the alphabet or numbers as pressed using keypad

by the user .The display device used here is (2x16)LCD which is interfaced

with microcontroller along with (4x4) keypad.

Microcontroller is a microprocessor with integrated along with input

output ports and memory in a single package.

Microcontroller has 4 input output Port 0,1,2,3 having 8 pins each.

LCD is connected to Port 1 and keypad with Port 2.The circuit require a 5

volt supply which is obtained using a power supply (connected to pin 40 of

microcontroller) circuit which takes an input of 230 volt AC and a 5 volt DC

supply is finally obtained in output .

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Circuit diagram

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Power Supply

Power supply is designed to convert high voltage AC mains electricity

to a suitable low voltage supply for electronics circuits and other devices. A

power supply can be broken down into a series of blocks, each of which

performs a particular function.

A 5V regulated supply:

Functions of the blocks is described below:

Transformer - steps down high voltage AC mains to low voltage AC.

Rectifier - converts AC to DC, but the DC output is varying.

Smoothing - smooths the DC from varying greatly to a small ripple.

Regulator - eliminates ripple by setting DC output to a fixed voltage.

Dual Supplies

Some electronic circuits require a power supply with positive and

negative outputs as well as zero volts (0V). This is called a 'dual supply'

because it is like two ordinary supplies connected together as shown in the

diagram.

Dual supplies have three outputs, for example a 9V supply has +9V, 0V

and -9V output.

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Transformer

Transformers convert AC electricity from one voltage to another with

little loss of power. Transformers work only with AC .

Step-up transformers increase voltage, step-down transformers reduce

voltage. Most power supplies use a step-down transformer to reduce thedangerously high mains voltage (230V) to a safer low voltage.

The input coil is called the primary and the output coil is called the

secondary. There is no electrical connection between the two coils, instead

they are linked by an alternating magnetic field created in the soft-iron core

of the transformer. The two lines in the middle of the circuit symbol

represent the core.

Transformers waste very little power so the power out is (almost) equal to

the power in. As voltage is stepped down current is stepped up.

The ratio of the number of turns on each coil, called the turns ratio,

determines the ratio of the voltages. A step-down transformer has a large

number of turns on its primary (input) coil which is connected to the high

voltage mains supply, and a small number of turns on its secondary (output)

coil to give a low output voltage.

Transformer circuit symbol

Transformer

Transformer only

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Bridge rectifier

A bridge rectifier can be made using four individual diodes, but it is

also available in special packages containing the four diodes required. It is

called a full-wave rectifier because it uses all the AC wave (both positive

and negative sections). 1.4V is used up in the bridge rectifier because eachdiode uses 0.7V when conducting and there are always two diodes

conducting, as shown in the diagram below. Bridge rectifiers are rated by the

maximum current they can pass and the maximum reverse voltage they can

withstand .

Transformer + Rectifier

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CapacitorSmoothing is performed by a large value electrolytic capacitor

connected across the DC supply to act as a reservoir, supplying current to

the output when the varying DC voltage from the rectifier is falling. The

diagram shows the unsmoothed varying DC (dotted line) and the smoothedDC (solid line). The capacitor charges quickly near the peak of the varying

DC, and then discharges as it supplies current to the output.

Smoothing is not perfect due to the capacitor voltage falling a little as it

discharges, giving a small ripple voltage. A larger capacitor will give less

ripple

Transformer + Rectifier + Smoothing

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Regulator

Voltage regulator ICs are available with fixed (typically 5, 12 and

15V) or variable output voltages. They are also rated by the maximum

current they can pass. Negative voltage regulators are available, mainly foruse in dual supplies. Most regulators include some automatic protection

from excessive current ('overload protection') and overheating ('thermal

protection').

Many of the fixed voltage regulator ICs have 3 leads and look like

power transistors, such as the 7805 +5V 1A regulator shown on the right.

They include a hole for attaching a heat sink .

Voltage regulator

Transformer + Rectifier + Smoothing + Regulator

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LED

A light-emitting diode, usually called an LED is a semiconductor

diode that emits incoherent narrow-spectrum light when electrically biased

in the forward direction of the p-n junction, as in the common LED circuit.

This effect is a form of electroluminescence.A LED is usually a small area light source, often with extra optics

added to the chip that shapes its radiation pattern.[2][3] LEDs are often used as

small indicator lights on electronic devices and increasingly in higher power

applications such as flashlights and area lighting. The color of the emitted

light depends on the composition and condition of the semiconducting

material used, and can be infrared, visible, or ultraviolet. LEDs can also be

used as a regular household light source.

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LCD

Liquid Crystal Display also called as LCD is very helpful in providing

user interface as well as for debugging purpose. The most common type of

LCD controller is HITACHI 44780 which provides a simple interface

between the controller & an LCD. These LCD's are very simple to interface

with the controller .The most commonly used ALPHANUMERIC displays are 1x16

(Single Line & 16 characters), 2x16 (Double Line & 16 character per line) &

4x20 ( four lines & Twenty characters per line).

Here we are using 2x16 alphanumeric display

The LCD requires 3 control lines (RS, R/W & EN) & 8 data lines. In 8-bit

mode 8 data lines + 3 control lines i.e. total 11 lines are required.

When RS is low (0), the data is to be treated as a command. When RS

is high (1), the data being sent is considered as text data which shouldbe displayed on the screen.

When R/W is low (0), the information on the data bus is being written

to the LCD. When RW is high (1), the program is effectively reading

from the LCD. Most of the times there is no need to read from the

LCD so this line can directly be connected to Gnd thus saving one

controller line.

The EN pin is used to latch the data present on the data pins. A HIGH

- LOW signal is required to latch the data. The LCD interprets and

executes our command at the instant the EN line is brought low. Ifyou never bring EN low, your instruction will never be executed.

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Pin Symbol Function

1 Vss Ground

2 Vdd Supply Voltage

3 Vo Contrast Setting

4 RS Register Select

5 R/WRead/Write

Select

6 EnChip Enable

Signal

7-14DB0-

DB7Data Lines

15 A/VeeGnd for the

backlight

16 K Vcc for backlight

Display Data Ram (DDRAM) stores the display data. So when we

have to display a character on LCD we basically write it into DDRAM. Fora 2x16 LCD the DDRAM address for first line is from 80h to 8fh & for

second line is 0c0h to 0cfh. So if we want to display 'H' on the 7 th position of

the first line then we will write it at location 87h.

Two types of data is given to the LCD data to be displayed, command or

special instruction.

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Data to be Displayed

LCD data display:

SETB RS //Telling the LCD that the data which is being

send is to be displayed

MOV P1,A //Character to be displayed is in Acc

SETB EN

CLR EN //High to Low pulse on EN to latch the data

CALL DELAY //Delay so that LCD finishes its internal

operations

Ret

Delay is used at the end of the subroutines, this is done to wait until theinstruction is completely executed by the LCD. This will assure that our

program gives the LCD the time it needs to execute instructions and also

makes our program compatible with any LCD, regardless of how fast or

slow it is.

"*" - Not Used/Ignored. This bit can be either "1" or "0"

Set Cursor Move Direction:

ID - Increment the Cursor After Each Byte Written to Display if Set

S - Shift Display when Byte Written to Display Enable Display/Cursor

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D - Turn Display On(1)/Off(0)

C - Turn Cursor On(1)/Off(0)

B - Cursor Blink On(1)/Off(0)

Move Cursor/Shift Display

SC - Display Shift On(1)/Off(0)

RL - Direction of Shift Right(1)/Left(0)

Set Interface Length

DL - Set Data Interface Length 8(1)/4(0)

N - Number of Display Lines 1(0)/2(1)

F - Character Font 5x10(1)/5x7(0)

Poll the "Busy Flag" BF - This bit is set while the LCD is processing

Move Cursor to CGRAM/Display

A - Address

Read/Write ASCII to the Display

D - Data

Debugging Procedure

If the above program does not work then follow these steps:-

1) Check if the supply is correct.

2)If all connections are correct.

3) Increase the delay time.

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Switches

A switch is a mechanical device used to connect and disconnect a

circuit at will. Switches cover a wide range of types, from subminiature upto industrial plant switching megawatts of power on high voltage

distribution lines.

A biased switch is one containing a spring that returns the actuator to

a certain position. The "on-off" notation can be modified by placing

parentheses around all positions other than the resting position. For example,

an (on)-off-(on) switch can be switched on by moving the actuator in either

direction away from the centre, but returns to the central off position when

the actuator is released.

The momentary push-button switch is a type of biased switch. Themost common type is a push-to-make switch, which makes contact when

the button is pressed and breaks when the button is released.

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Keypad Connections with 8051

Microcontroller

Circuit shown above is for demonstration and does not include any reset and

crystal circuit. For practical use you need to have a reset circuit and crystal.

Introduction

Keypads are a part of HMI or Human Machine Interface and play really

important role in a small embedded system where human interaction or

human input is needed. Matrix keypads are well known for their simple

architecture and ease of interfacing with any microcontroller.

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Constructing a Matrix Keypad

Construction of a keypad is really simple. As per the outline shown in the

figure below we have four rows and four columns. In between eachoverlapping row and column line there is a key.

So keeping this outline we can constuct a keypad using simple SPSTSwitches as shown below:

Now our keypad is ready, all we have to do is connect the rows and columnsto a port of microcontroller and program the controller to read the input.

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Scanning a Matrix Keypad

There are many methods depending on how you connect your keypad with

your controller, but the basic logic is same. We make the coloums as i/p and

we drive the rows making them o/p, this whole procedure of reading thekeyboard is called scanning.

In order to detect which key is pressed from the matrix, we make row lines

low one by one and read the columns. Lets say we first make Row1 low

,then read the columns. If any of the key in row1 is pressed will make the

corresponding column as low i.e if second key is pressed in Row1, then

column2 will give low. So we come to know that key 2 of Row1 is pressed.

This is how scanning is done.

So to scan the keypad completely, we need to make rows low one by one

and read the columns. If any of the button is pressed in a row, it will take the

corresponding column to a low state which tells us that a key is pressed in

that row. If button 1 of a row is pressed then Column 1 will become low, if

button 2 then column2 and so on...

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MicrocontrollerFeatures

Compatible with MCS-51 Products

4K Bytes 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

128 x 8-Bit Internal RAM

32 Programmable I/O Lines

Two 16-Bit Timer/Counters

Six Interrupt Sources

Programmable Serial Channel

Low Power Idle and Power Down Modes

Description

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 Atmels 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 withFlash 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: 4Kbytes of Flash,

128 bytes of RAM, 32 I/O lines, two 16-bittimer/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 selectablepower 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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Pin DescriptionPin configuration of 8051/8031 microcontroller.

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VCC : Supply voltage.

GND: Ground.

Port 0

Port 0 is an 8-bit open drain bidirectional I/O port. As an output port each

pin can sink eight TTL inputs. When 1s are written to port 0 pins, the pins

can be used as high impedance inputs.

Port 0 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 pullups. Port 0 also receives the code bytes during Flash

programming, and outputs the code bytes during program verification.

Port 1

Port 1 is an 8-bit bidirectional I/O port with internal pullups.The Port 1output buffers can sink/source four TTL inputs.When 1s are written to Port 1

pins they are pulled high by the internal pullups and can be used as inputs.

As inputs, Port 1 pins that are externally being pulled low will source current

(IIL) because of the internal pullups. Port 1 also receives the low-order

address bytes during Flash programming and verification.

Port 2

Port 2 is an 8-bit bidirectional I/O port with internal pullups. The Port 2

output buffers can sink/source four TTL inputs. When 1s are written to Port

2 pins they are pulled high by the internal pullups and can be used as inputs.


(IIL) because of the internal pullups. Port 2 emits the high-order address

byte during fetches from external program memory and during accesses to

external data memory that use 16-bit addresses (MOVX @ DPTR). In this

application it uses strong internal pull-ups .when emitting 1s. During

accesses to external data memory that use 8-bit addresses (MOVX @ RI),

Port 2 emits the contents of the P2 Special Function Register. Port 2 also

receives the high-order address bits and some control signals during Flash

programming and verification.

Port 3

Port 3 is an 8-bit bidirectional I/O port with internal pullups. The Port 3

output buffers can sink/source four TTL inputs. When 1s are written to Port

3 pins they are pulled high by the internal pullups and can be used as inputs.


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(IIL) because of the pullups. Various special features of the AT89C51 as

listed below:

Port Pin Alternate Functions

P3.0 RXD (serial input port)

P3.1 TXD (serial output port)

P3.2 INT0 (external interrupt 0)

P3.3 INT1 (external interrupt 1)

P3.4 T0 (timer 0 external input)

P3.5 T1 (timer 1 external input)

P3.6 WR (external data memory write strobe)

P3.7 RD (external data memory read strobe)

Port 3 also receives some control signals for Flash programming andverification.

RST

Reset input. A high on this pin for two machine cycles while the oscillator is

running resets the device.

ALE/PROG

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. 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 AT89C51 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.

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EA/V PP

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.

XTAL1

Input to the inverting oscillator amplifier and input to the internal clock

operating circuit.

XTAL2Output from the inverting oscillator amplifier.

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