Why here is ' symbol before and after letter?

Projects Programming
1

Here is the code (from Arduino website)

/*
LiquidCrystal Library - TextDirection

Demonstrates the use a 16x2 LCD display.  The LiquidCrystal
library works with all LCD displays that are compatible with the
Hitachi HD44780 driver. There are many of them out there, and you
can usually tell them by the 16-pin interface.

This sketch demonstrates how to use leftToRight() and rightToLeft()
to move the cursor.

The circuit:
* LCD RS pin to digital pin 12
* LCD Enable pin to digital pin 11
* LCD D4 pin to digital pin 5
* LCD D5 pin to digital pin 4
* LCD D6 pin to digital pin 3
* LCD D7 pin to digital pin 2
* LCD R/W pin to ground
* 10K resistor:
* ends to +5V and ground
* wiper to LCD VO pin (pin 3)

Library originally added 18 Apr 2008
by David A. Mellis
library modified 5 Jul 2009
by Limor Fried (http://www.ladyada.net)
example added 9 Jul 2009
by Tom Igoe
modified 22 Nov 2010
by Tom Igoe

This example code is in the public domain.

http://arduino.cc/en/Tutorial/LiquidCrystalTextDirection

*/

// include the library code:
#include <LiquidCrystal.h>

// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

int thisChar = 'a';          //why here is 'a', not just a. What it changes?

void setup() {
  // set up the LCD's number of columns and rows:
  lcd.begin(16, 2);
  // turn on the cursor:
  lcd.cursor();
}

void loop() {
  // reverse directions at 'm':
  if (thisChar == 'm') {
    // go right for the next letter
    lcd.rightToLeft();
  }
  // reverse again at 's':
  if (thisChar == 's') {
    // go left for the next letter
    lcd.leftToRight();
  }
  // reset at 'z':
  if (thisChar > 'z') {
    // go to (0,0):
    lcd.home();
    // start again at 0
    thisChar = 'a';
  }
  // print the character
  lcd.write(thisChar);
  // wait a second:
  delay(1000);
  // increment the letter:
  thisChar++;
}
2

'a' means LITERALLY the character 'a' whereas a on it's own would be the name of a variable, even if you haven't defined a variable the name a

3

'a' designates the ascii charater a. Remember variables hold numeric values. The value for 'a' is decimal 97 or hex 61. These are just other ways of expressing the same value. This is why the construct

thisChar++;

works. There is a lot of documentation for ascii code on the internet

using a symbol without single quotes means you are referring to a variable not a literal value

4 
/*
LiquidCrystal Library - TextDirection

Demonstrates the use a 16x2 LCD display.  The LiquidCrystal
library works with all LCD displays that are compatible with the
Hitachi HD44780 driver. There are many of them out there, and you
can usually tell them by the 16-pin interface.

This sketch demonstrates how to use leftToRight() and rightToLeft()
to move the cursor.

The circuit:
* LCD RS pin to digital pin 12
* LCD Enable pin to digital pin 11
* LCD D4 pin to digital pin 5
* LCD D5 pin to digital pin 4
* LCD D6 pin to digital pin 3
* LCD D7 pin to digital pin 2
* LCD R/W pin to ground
* 10K resistor:
* ends to +5V and ground
* wiper to LCD VO pin (pin 3)

Library originally added 18 Apr 2008
by David A. Mellis
library modified 5 Jul 2009
by Limor Fried (http://www.ladyada.net)
example added 9 Jul 2009
by Tom Igoe
modified 22 Nov 2010
by Tom Igoe

This example code is in the public domain.

http://arduino.cc/en/Tutorial/LiquidCrystalTextDirection

*/

// include the library code:
#include <LiquidCrystal.h>

// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

int thisChar = 'a';

void setup() {
  // set up the LCD's number of columns and rows:
  lcd.begin(16, 2);
  // turn on the cursor:
  lcd.cursor();
}

void loop() {
  // reverse directions at 'm':
  if (thisChar == 'm') {
    // go right for the next letter
    lcd.rightToLeft();
  }
  // reverse again at 's':
  if (thisChar == 's') {
    // go left for the next letter
    lcd.leftToRight();
  }
  // reset at 'z':
  if (thisChar > 'z') {
    // go to (0,0):
    lcd.home();
    // start again at 0
    thisChar = 'a';
  }
  // print the character
  lcd.write(thisChar);
  // wait a second:
  delay(1000);
  // increment the letter:
  thisChar++;
}

So, I put there 'a', but lcd prints.... 98???? Why?

6

Code:

/*-----( Import needed libraries )-----*/
#include <LiquidCrystal.h>

/*-----( Declare objects )-----*/
LiquidCrystal lcd(2, 3, 4, 5, 6, 7); //These are the pins used on this shield

/*-----( Declare Constants )-----*/
#define btnRIGHT  0
#define btnUP     1
#define btnDOWN   2
#define btnLEFT   3
#define btnSELECT 4
#define btnNONE   5

/*-----( Declare Variables )-----*/
int lcd_key       = 0;
int adc_key_in    = 0;
int adc_key_prev  = 0;
byte numbChar      = '0';
int lettChar      = 'a';

void setup()   /*----( SETUP: RUNS ONCE )----*/
{
  lcd.begin(16, 2);              // start the lcd object
  
}/*--(end setup )---*/

void loop()   /*----( LOOP: RUNS CONSTANTLY )----*/
{
  adc_key_prev = lcd_key ;       // Looking for changes
  lcd_key = read_LCD_buttons();  // read the buttons

  lcd.setCursor(0,1);            // move to the begining of the second line

  switch (lcd_key)               // depending on which button was pushed, we perform an action
  {
  case btnRIGHT:
    {
      lcd.setCursor(10, 1);
      lcd.print("  ");
      numbChar++;
      lcd.setCursor(9, 1);
      lcd.print(numbChar);
      delay(250);
      break;
    }
  case btnLEFT:
    {
      lcd.setCursor(10, 1);
      lcd.print("  ");
      numbChar--;
      lcd.setCursor(9, 1);
      lcd.print(numbChar);
      delay(250);
      break;
    }
  case btnUP:
    {
      lcd.print("UP    ");
      break;
    }
  case btnDOWN:
    {
      lcd.print("DOWN  ");
      break;
    }
  case btnSELECT:
    {
      lcd.print("SELECT");
      break;
    }
  case btnNONE:
    {
      lcd.print("NONE  ");
      break;
    }
  }/* --(end switch )-- */

}/* --(end main loop )-- */

/*-----( Declare User-written Functions )-----*/

int read_LCD_buttons()
{
  adc_key_in = analogRead(0);      // read the value from the sensor 
  delay(5); //switch debounce delay. Increase this delay if incorrect switch selections are returned.
  int k = (analogRead(0) - adc_key_in); //gives the button a slight range to allow for a little contact resistance noise
  if (5 < abs(k)) return btnNONE;  // double checks the keypress. If the two readings are not equal +/-k value after debounce delay, it tries again.
  // my buttons when read are centered at these valies: 0, 144, 329, 504, 741
  // we add approx 50 to those values and check to see if we are close
  if (adc_key_in > 1000) return btnNONE; // We make this the 1st option for speed reasons since it will be the most likely result
  if (adc_key_in < 50)   return btnRIGHT;  
  if (adc_key_in < 195)  return btnUP; 
  if (adc_key_in < 380)  return btnDOWN; 
  if (adc_key_in < 555)  return btnLEFT; 
  if (adc_key_in < 790)  return btnSELECT;   
  return btnNONE;  // when all others fail, return this...
}

Why then it doesn't print on lcd 0, 1, 2, 3..., but 48, 49, 50, 51....

7

I found where I was wrong :slight_smile: . I wrote in my code lcd.print, not lcd.write.

When I wrote lcd.write, it fixes :slight_smile:

Thanks for all, who helped

8

Delta_G:
When you print an int it prints the decimal value. If you want to print it as ascii then put it in a char variable. Print sees char variables and makes the assumption that you want ascii.

You can cast the int to char.

int x =48;

Serial.print(( char ) x ); // should print "0"