Session 5: LCD and KeyPad

Goal

Bonus point

• enter password

• type * instead of actual character

• D: clear the input

• E: submit your password

LCD

LCD is used to write parameters and status. We have a 16x2 LCD (16 columns and 2 rows). It has 16-pins.

VSS	VCC	VEE
Ground	5V+	Contrast Control

RS	RW	E
Register select	Read / Write	Enable

D0	D1	D2	D3	D4	D5	D6	D7
Data pin 0	Data pin 1	Data pin 2	Data pin 3	Data pin 4	Data pin 5	Data pin 6	Data pin 7

LED+	LED-
LED 5V+	LED Ground

Connect LCD on SimulIDE

In SimulIDE we can select an LCD from /outputs/displays/HD44780 and connect it to the ATmega32. We connect the pins like this:

• RS PC3

• RW PD7

• EN PD6

• D4 PB4

• D5 PB5

• D6 PB6

• D7 PB7

So the result would be like the image below:

LCD library and header file

For LCD library, We have a directory called lcd_library which have two files:

• lcd_library.h

• lcd_library.cpp

To use them in our project we shoud copy the whole directory of lcd_library to the lib directory of our PlatformIO project. Then we are going to be able to import it using the code below:

#include <lcd_library.h>

This library has 6 functions, that we are going to explain about them more.

lcd_init

initializes our LCD. Sets DDRs and PORTs required for the LCD to function.

Synopsis:

void lcd_init();

Example:

lcd_init();

lcd_gotoxy

Goes to a position on LCD.

Synopsis:

void lcd_gotoxy(unsigned char row, unsigned char col)

Arguments:

• row: row position

• col: column position

Example:

lcd_gotoxy(1, 5);

lcd_putchar

Puts a charachter in a current position of the LCD.

Synopsis:

void lcd_putchar(unsigned char data);

Arguments:

• data: Character that we want to write on the LCD

Example:

lcd_putchar('p');

lcd_puts

Puts a string in a current position of the LCD. If it exceeds, goes back to the 0 column.

Synopsis:

void lcd_puts(const char *str);

Arguments:

• str: String that we want to write on the LCD

Example:

lcd_puts("hello");

lcd_clear

Clears the LCD

Synopsis:

void lcd_clear();

Example:

lcd_clear();

lcd_commad

Sends a command to the LCD.

Synopsis:

void lcd_command(unsigned char cmd);

Arguments:

• cmd: Command that we want to send to the LCD

Example:

// to clear the display:
lcd_command(0x01);

PIN

We use PIN variable to read data of a pin.

For example:

char x = PINA;

Keypad

As you can see on the image above, the way that each key is connected to ATmega32 is shown.

col0	col1	col2	col3	row0	row1	row2	row3
PA.0	PA.1	PA.2	PA.3	PA.4	PA.5	PA.6	PA.7

Important

We put 1 in all the pins.

Detect one key (row0, col0)

In order to detect which key is pressed we start with one key.

As you can see on the image above if I put 0 in PORTA.4:

• If the key is pressed: PINA.0 = 0

• If the key is not pressed: PINA.0 = 1

The simulation would be like below:

Detect a row of keys (row0)

Now we try to detect a row of keys.

As you can see on the image above if I put 0 in PORTA.4:

• If the key in col0 is pressed: PINA.0 = 0

• If the key in col1 is pressed: PINA.1 = 0

• If the key in col2 is pressed: PINA.2 = 0

• If the key in col3 is pressed: PINA.3 = 0

The simulation would be like below:

Detect all keys

To detect all keys we can run a for on PORTA.4 to PORTA.7