void loop()
{
  //Le o valor do pino do sensor
  ValorAtual = digitalRead(sensor);

  if(ValorAtual == 1 && ValorAnterior == 0)
  {
      ClosedDoor();
      ValorAnterior == 1;
  }

  if(ValorAtual == 0 && ValorAnterior == 1)
  {
      OpenedDoor();
      ValorAnterior == 0;
  }

}

Introduction

In several places, security systems are needed to protect rooms. For this, we need to install equipment that protects the place and, for example, generates an alert to notify that the room has been accessed by someone.

One way to solve this problem is to use the Arduino with the reed switch sensor. That is, when someone opens the door, a person will receive an alert via SMS on their cell phone.

This message will be sent through the SIM800L GSM Module. The circuit is presented in Figure 1.

Figure 1 - Circuit with SIM800L and Reed Switch to detect opened door.

Now, you'll learn how to create the project step by step.

The step by step of the Project

Firstly, we'll explain how works the project. You need to install your reed switch sensor and a magnet in your door. And hereafter, you'll connect the sensor in your Arduino System.

When the door is opened, the magnet will move away from the reed switch sensor and it will open. In this way, the system will detect that the door has been opened and will send a SMS through SIM800L for the user.

The circuit in the breadboard is presented below.

Figure 1 - Circuit to detect opened door in the Breadboard.

Based on this problem, we'll construct the project through the following code presented below.

The Source Code of the Project

Below, you can see the source code of this project. Hereafter, we'll present the step by step of this code.

#include <SoftwareSerial.h>
SoftwareSerial chip(10, 11);

String SeuNumero = "+xxxxxxxxxxxxx";

#define sensor 12

bool ValorAtual = 0, ValorAnterior = 0;

void setup()
{
  Serial.begin(9600);
  Serial.println("Inicializando Sistema...");
  delay(5000);
  chip.begin(9600);
  delay(1000);

  pinMode(sensor, INPUT); //Configura o Pino do Sensor como Entrada
}

void loop()
{
  //Le o valor do pino do sensor
  ValorAtual = digitalRead(sensor);

  if(ValorAtual == 1 && ValorAnterior == 0)
  {
      ClosedDoor();
      ValorAnterior == 1;
  }

  if(ValorAtual == 1 && ValorAnterior == 0)
  {
      OpenedDoor();
      ValorAnterior == 0;
  }

}

void OpenedDoor() //Funcao para enviar mensagem de alerta Umidade Baixa
{
  chip.println("AT+CMGF=1");
  delay(1000);
  chip.println("AT+CMGS=\"" + SeuNumero + "\"\r");
  delay(1000);
  String SMS = "Opened Door!";
  chip.println(SMS);
  delay(100);
  chip.println((char)26);
  delay(1000);
}

void ClosedDoor()//Funcao para enviar mensagem de alerta Umidade Normal
{
  chip.println("AT+CMGF=1");
  delay(1000);
  chip.println("AT+CMGS=\"" + SeuNumero + "\"\r");
  delay(1000);
  String SMS = "Closed Door!";
  chip.println(SMS);
  delay(100);
  chip.println((char)26);
  delay(1000);
}

 For this project, we use library SoftwareSerial. The library will be used to communicate the Arduino with SIM800L Module through serial communication.

#include <SoftwareSerial.h>

Next, we'll define what is the pin in the Arduino that will be used like a RX and TX serial communication. 

SoftwareSerial chip(10, 11);

Subsequently, we need to create a string and add the mobile number to that string. You must enter the + Country Code and your cellphone number after the country code.

String SeuNumero = "+xxxxxxxxxxxxx";

After, it was defined as the sensor pin and the variables of the code.

#define sensor 12

bool ValorAtual = 0, ValorAnterior = 0;

Finally, is executed the setup function in the Arduino.

The function void setup() and void loop() in Arduino

In the serial communication will be initialized the serial of the Arduino pins (digital pin 0 and digital pin 1) and the virtual serial through the library SoftwareSerial with the object chip.

void setup()
{
  Serial.begin(9600);
  Serial.println("Inicializando Sistema...");
  delay(5000);
  chip.begin(9600...