send SMS for 1 time with arduino GPRS SIM900 if an iput is HIGH

Question

I faced a problem to send 1 SMS if an input is HIGH,and if it is LOW==> no SMS to send,if LOW to HIGH==> send 1 SMS. this code not working,just sent SMS when I turn the GPRS on,and after nothing is happened.

mclopez helped me,thank you,but not working :( , this is the new code that I wrote with the delay()s,but the same problem.

Thank you for helping in advance.

   #include <SoftwareSerial.h>
   #include "TimerOne.h"

   const int DI = 2;
   const int DT = 3;
   const int DGP1 = 4;
   const int DGP2 = 5;
   const long interval = 100000; // in microseconds

   int value1 = 0;
   int value2 = 0;
   int value3 = 0;
   int value4 = 0;

   int value1_old = 0;
   int value2_old = 0;
   int value3_old = 0;
   int value4_old = 0;

   boolean changed1 = false;
   boolean changed2 = false;
   boolean changed3 = false;
   boolean changed4 = false;

   SoftwareSerial SIM900 (7, 8);

   void SIM900power(){
     digitalWrite(9, HIGH);
     delay(1000);
     digitalWrite(9, LOW);
     delay(5000);
   }

  void initia(){
  SIM900.print("AT+CMGF=1\r");
  delay(100);
  SIM900.println("AT + CMGS = \"xxxxxxxxxx\"");
  delay(100);
  }

  void Send_SMS(){
  SIM900.println((char)26);
  delay(100);
  SIM900.println();
  delay(5000);

 }

  void isr_timer(){
    if (changed2) {
    initia();
    SIM900.println("Station 85: Defaut electrique");
    delay(100);
    Send_SMS();
    value2_old = value2;
    changed2 = false;
  }  

  if (changed3) {
    initia();
    SIM900.println("Station 85: DefautGP1");
    delay(100);
    Send_SMS();
    value3_old = value3;
    changed3 = false;
   }

   if (changed4) {
     initia();
     SIM900.println("Station 85:DD>1000");
     delay(100);
     Send_SMS();
     value4_old = value4;
     changed4 = false;
    }
 }

  void setup() {
   pinMode(DI, INPUT);
   pinMode(DT, INPUT);
   pinMode(DGP1, INPUT);
   pinMode(DGP2, INPUT);

   SIM900.begin(19200);
   Timer1.initialize(interval);
   Timer1.attachInterrupt(isr_timer);
  }

 void loop() {
   value1 = digitalRead (DI);
   value2 = digitalRead (DT);
   value3 = digitalRead (DGP1);
   value4 = digitalRead (DGP2);

   if (value1 != value1_old && value1 == HIGH) changed1 = true;
   if (value2 != value2_old && value2 == HIGH) changed2 = true;
   if (value3 != value3_old && value3 == HIGH) changed3 = true;
   if (value4 != value4_old && value4 == HIGH) changed4 = true;

   value1_old = value1;
   value2_old = value2;
   value3_old = value3;
   value4_old = value4;

 }

Answer 1

Try slowing down the interval on the interrupt. It is possible that due to several if statements running under isr_timer()that the main loop may be locking up. I have a sneaking suspicion you are trying to do too much!

Be careful about trying to execute too complicated of an interrupt at too high of a frequency, or the CPU may never enter the main loop and your program will 'lock up'. Reference

Saying that and to check that your main loop is actually running why not add a simple debug at the bottom of the main loop() to flash the on board led..

int onBoardLED = 13;

void setup()
 {
    pinMode(onBoardLED, OUTPUT);

    // And all the rest
 } 

void loop()
 {
    // Doing stuff

    if (onBoardLED == LOW) digitalWrite(ledPin, HIGH);
    else digitalWrite(ledPin, LOW);
 }

At least then you will know if the main loop() is even actually executing. It obviously runs once as you are getting a single SMS through but really with no other way of telling its a guess after that...

If all looks good try adding some further flags around the place just to see whats getting executed and what is not. Other than that suggestion i cant spot anything further but interested to find out! Best of luck

Update
Just dug this link out of my bookmarks. You may find it useful.
- Nick Gammon - Interrupts