16x2 LCD 1602 Keypad Shield for Arduino Yellow-Green Screen/Backlight

Demo Sketch

/*
  The circuit:
 * LCD RS pin to digital pin 8
 * LCD Enable pin to digital pin 9
 * LCD D4 pin to digital pin 4
 * LCD D5 pin to digital pin 5
 * LCD D6 pin to digital pin 6
 * LCD D7 pin to digital pin 7
 * LCD BL pin to digital pin 10
 * KEY pin to analogl pin 0
 */

#include <LiquidCrystal.h>

LiquidCrystal lcd(8, 13, 9, 4, 5, 6, 7);

char msgs[5][16] = {
  "Right Key OK ",
  "Up Key OK    ",               
  "Down Key OK  ",
  "Left Key OK  ",
  "Select Key OK" };

int adc_key_val[5] = {50, 200, 400, 600, 800 };
int NUM_KEYS = 5;
int adc_key_in;
int key = -1;
int oldkey = -1;

void setup()
{
  lcd.clear(); 
  lcd.begin(16, 2);
  lcd.setCursor(0,0); 
  lcd.print("Shield key test:"); 
}

void loop()
{
  adc_key_in = analogRead(0);      // read the value from the sensor 
  key = get_key(adc_key_in);       // convert into key press
 
  if (key != oldkey) {             // if keypress is detected
    delay(50);                     // wait for debounce time
    adc_key_in = analogRead(0);    // read the value from the sensor 
    key = get_key(adc_key_in);     // convert into key press
    if (key != oldkey) {   
      lcd.setCursor(0, 1);
      oldkey = key;
      if (key >=0) {
           lcd.print(msgs[key]);              
      }
    }
  }

  delay(100);
}

// Convert ADC value to key number
int get_key(unsigned int input)
{
    int k;
   
    for (k = 0; k < NUM_KEYS; k++) {
      if (input < adc_key_val[k])
        return k;
    }
   
    if (k >= NUM_KEYS)             // No valid key pressed
      k = -1;

    return k;
}