Previous Millis - Blink without delay : Action Email THEN countdown.

Using Arduino Programming Questions
1

I am losing my mind and now unable to figure out what to google to self sooth - feels like i have tried everything.

I am trying to trigger sending an Email based on an event (temperature) using previousMillis.

The timer works perfect - with only one problem... the "const long interval = 360000;" delays the action UNTILL that time has past. So in the situation of 1 hour delay before a repeat it takes an hour to send the first email, before waiting an hour to repeat IF the statement is still true.

So simply put - how do i make previousMillis fire the action THEN start the countdown to prevent it spamming my email for 1 hour delay?

unsigned long previousMillis = 0;
const long interval = 360000;

// IF STATMENT MILLIS TIMER //
if (currentMillis - previousMillis >= interval) {
 previousMillis = currentMillis;
//}
  //
 //p.runShellCommand("cat /mnt/sda1/mail.txt | ssmtp an.email.address@gmail.com  2>&1");
 Serial.print('\n');
 Serial.print("-------------------------------------------------IT HAS SENT After Timer-----------------------------------------");
2 
Serial.print("-------------------------------------------------IT HAS SENT After Timer-----------------------------------------");

I hope the rest of your code doesn't exhibit such a flagrant disregard for the limitations of tiny microcontroller RAM.

3

I am currently using 2 different no delay timers depending upon needs.
So hears how to determine which to use.
If you have any long delays that could hold up the code for more than t (time in milliseconds) then you may not want to use the first because it will repeat until _ETimer catches up to millis()

I use the second for a spam timer because even in the code locks on a while loop looking for input it won,t spam the serial port when it starts looping again. Both are good and both have their purpose.

unsigned long t = 1000 // 1 second

// Exact intervals  
 static unsigned long _ETimer;
  if ( millis() - _ETimer >= (t)) {
    _ETimer += (t);
 // place your timed code here
  }

// After Interval ( t (time) or more will pass before this runs again)
  static unsigned long _ATimer;
  if ( (unsigned long)(millis() - _ATimer) >= (t)) {
    _ATimer = millis();
// place your timed code here
  }
4 
    // IF STATMENT MILLIS TIMER //
    if (currentMillis - previousMillis >= interval || previousMillis == 0) {
        previousMillis = currentMillis;


         // p.runShellCommand("cat /mnt/sda1/mail.txt | ssmtp an.email.address@gmail.com  2>&1");

         Serial.println();
         Serial.println(F("--------------------------IT HAS SENT -----------------------------"));
    }