JTAG : Its only used during the production of the board.
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Arduino Alarm System

Arduino code:

/*
  LiquidCrystal Library – Hello World
 
Demonstrates the use a 16×2 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.
 
 
 
  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://www.arduino.cc/en/Tutorial/LiquidCrystal
*/

// include the library code:
#include <LiquidCrystal.h>
const int buttonPin = 8;
const int buttonPin1 = 9;// the number of the pushbutton pin
const int red =  7;      // the number of the LED pin
const int green =  6;
// variables will change:
int buttonState = 0;
int buttonState1 = 0;
// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

void setup() {
  pinMode(red, OUTPUT); 
  pinMode(green, OUTPUT); 
  // set up the LCD’s number of columns and rows:
  lcd.begin(16, 4);
  lcd.print(“System: Armed   “);
  // Print a message to the LCD.
  lcd.setCursor(-4, 3);
  lcd.print(” MTech Security”);
  digitalWrite(red, HIGH);
}

void loop() {
 
 
   buttonState = digitalRead(buttonPin);
buttonState1 = digitalRead(buttonPin1);
  // check if the pushbutton is pressed.
  // if it is, the buttonState is HIGH:
  if (buttonState1 == HIGH) {    
    // turn LED on:   
     lcd.setCursor(0, 0);
  lcd.print(“System: Disarmed”);
  digitalWrite(red, LOW);
  digitalWrite(green, HIGH);
  delay(30000);
  lcd.setCursor(0, 0);
  lcd.print(“System: Armed   “);
  }
  else {
    if (buttonState == HIGH) {    
    // turn LED on:   
    
  }
  else {
    lcd.setCursor(0, 0);
  lcd.print(“System: Tripped”);
   
    digitalWrite(red, HIGH);
     digitalWrite(green, LOW);
  }
   
   
  }

  // set the cursor to column 0, line 4

  // (note: line 1 is the second row, since counting begins with 0):
  lcd.setCursor(0, 3);
  lcd.print(“”);
  // print the number of seconds since reset:
 
}

 

Schematic: Coming TomorrowSmile