How to manage two alarms with one interrupt?

Question

I have a datalogger using the RTC DS3231 as an interrupt generator. I am able to have the interrupts work but here is my problem. I would like to take 2 separate measures from 2 different sensors (one for humidity, temperature and the other for accelerations), one every 30 min et one every hour, the thing is that because I use the same pin (only one pin from the DS3231) for both of these alarms I cannot use a simple counter in my interrupt function otherwise one measure will not be taken when both of the alarms will trigger...

For example I just did a quick test with one alarm each min when seconds are 00 and an other alarm each minute when seconds are 20. The problem as I said is that I cannot increment counters for each since I use the same interrupt function (because of the single pin). Here is my loop function and interrupt handling function :

void loop() {
  delay(1000);
  sleepNow();
  if (alarm == true){
    handleAlarm(); // reset the possibility to trigger alarm
    if (counter_dtphl == COUNT_DTPHL){
      take_measure_DTPHL();
      counter_dtphl = 0;
    }
    else if (counter_accel == COUNT_ACCEL){
      take_measure_ACCEL();
      counter_accel = 0;
    }
  }
}

void wakeUpNow() {  
  Serial.println("In wake up now");
  delay(100);
  alarm = true;
  //Serial.println(counter);
  sleep_disable();//Disable sleep mode
  byte sec = get_date(SEC);
  Serial.println(sec);
  if (sec == 0){
  counter_dtphl +=1;
  }
  else if (sec == 30){
  counter_accel +=1;
  }
  detachInterrupt(digitalPinToInterrupt(interruptPin)); //Removes the interrupt from pin 2;
}

void handleAlarm() {
  alarm = false; 
  rtcObject.LatchAlarmsTriggeredFlags();
}

COUNT_ACCEL and COUNT_DTPHL are constant having the value of minutes corresponding to the trigger for the measure.

Has anybody an idea how to manage this situation ? For the acceleration I need to save the data for a period of 30 sec. One solution I tried is to increment the counter according to the time in second that corresponds each minute but I cannot put it in the wakeUpNow function since only fast processing should be done there (it is the function executed by the interrupt).

Thank you for your time !

Answer 1

Consider it is good practice to leave as little code in an interrupt as possible. In this case, as the time in question is much greater then how often the loop() function is called, setting a single flag indicating an interrupt occurred would be sufficient.

Each time in your loop() function test for this flag. If TRUE, immediately set it to FALSE so as not forget to do so later. Next, while still in the scope of the IF statement, assuming the RTC DS3231 has been configured to create an interrupt every 30 minutes, take your "30 minute sample". Next, while still in the scope of the IF statement, increment a counter. Make sure this counter is defined as a global variable in order to persist between calls to the loop() function. If this counter has reached the value of 2, clear this counter to zero and take your "60 minute sample".

Consider the following pseudo code:

// Global variable defined outside of functions to track state & time.
bool state_interrupts;
int counter_interrupts;

void setup()
{
  // Initialize RTC to generate an interrupt once every 30 minutes.
  <RTC initialization code.>
  // Call attach interrupt to identify interrupt function name "wakeUpNow".
  attachInterrupt(...)
  // Initialize state & counter;
  interrupts_state = false;
  interrupts_counter = 0; 
}

void loop()
{
  // Check if interrupt occurred.
  if(interrupts_state)
  {
    interrupts_state = false;
    interrupts_counter++;
    // Sample 30 minute sensor.
    <Sample 30 minute sensor code.>
    if(interrupts_counter >= 2)
    {
      interrupts_counter = 0;
      // Sample 60 minute sensor.
      <Sample 60 minute sensor code.>
    }
  }
}

void wakeUpNow()
{
    interrupts_state = true;
}

Answer 2

The typical solution to this type of problem is:

1. In the ISR set a flag to indicate an RTC interrupt has occurred.
2. In the loop check the flag and if the set: a) Read the alarm flags from the RTC, b) Check the alarms, return value from LatchAlarmsTriggeredFlags(), and do the appropriate action.

What you should not do is write a lot of code in the ISR. Especially code that is also interrupt driven or depend on interrupts such as Wire, Serial, millis(), delay(), etc.

Cheers!

Answer 3

After the interrupt read the time from the RTC and then do the correct thing based on the result.

Answer 4

Try this: bool x = true; This is before setup bool done = false;

x = !x; Do this in the interrupt function. done = true; this is in your loop! if done == true{ // Determine if you have been here before if X !true do both functions else do the 30 second one I use the !X as it is faster. done = false;} This should give you an idea, I did not actually code this but i use code similar to this all the time. My goal is to do no more then 1 or two instructions in the interrupt service routine (ISR).