ISR Timer 1 second

[aless81]

Guys, does anyone have an example of how I configure the timer to generate an interrupt every 1 second.

[LarryD]

• Please be more explicit.

FYI

Using millis() for timing. A beginners guide

Part 1 It is not usually long before new Arduino users discover that although the delay() function is easy to use it has side effects, the main one of which is that its stops all activity on the Arduino until the delay is finished (not quite true, I know, but that is usually how the problem presents itself). When this occurs the new user is usually directed to the BlinkWithoutDelay example sketch (BWoD) and/or the excellent thread entitled Several things at the same time. Several things at the…

[dougp]

Which processor? Which timer?

[aless81]

I have a program that reads the pulses received on a pin through an interrupt and counts them. This part works well.

I made a routine using millis() to display the count value every 1 second and reset it to zero. It works well too.

But unfortunately I had to add some delay() at some point in the program, which causes the routine using millis() to sometimes be executed well after 1s.

So I would like to learn how to use the timer, I don't know which one to generate an interrupt every 1s.

Arduino UNO 16MHz

[aless81]

I would like to do this if I use a library.

I don't know which timer the Arduino UNO uses for the delay() and millis() function and also which timer the PWM uses. So I'm afraid of changing some timer that I shouldn't

[jremington]

@aless81

which timer the Arduino UNO uses for the delay() and millis() function

Timer0. PWM uses Timers 1 and 2.

[LarryD]

@aless81

But unfortunately I had to add some delay() at some point in the program

• This is 99.9% never necessary.

---

In the Arduino IDE, use Ctrl T or CMD T to format your code then copy the complete sketch.
Use the < CODE / > icon from the ‘posting menu’ to attach the copied sketch.

[DaveX]

Code?

How close to a second is close enough?

Re:

@aless81

But unfortunately I had to add some delay() at some point in the program, which causes the routine using millis() to sometimes be executed well after 1s.

Getting rid of the delay will likely pay off, and then you might not need an interrupt.

If you still want an interrupt, this trick takes advantage of the already-configured timer0 to give free 976.5625Hz interrupts:

Multi-tasking the Arduino - Part 2

[aless81]

Precision is not very important, as the number of pulses I will receive in one second will not be greater than 50, so if in one second I have 49, 50, 51 pulses counted in one second it will not be a problem.

[DaveX]

Well, here's the Adafruit timer0 multitasking example modified to do the guts of BlinkWithoutDelay inside an ISR:

// using an interrupt to do a 1 second process
// https://wokwi.com/projects/396818172976688129
//
// Built from
// https://learn.adafruit.com/multi-tasking-the-arduino-part-2/timers
// modified to do the code work of Blink without delay inside an ISR
// https://docs.arduino.cc/built-in-examples/digital/BlinkWithoutDelay/

const int ledPin = LED_BUILTIN;  // the number of the LED pin
const long interval = 1000;  // interval at which to blink (milliseconds)
byte ledState = LOW;  // ledState used to set the LED
volatile unsigned long previousMillis = 0;  // will store last time LED was updated

void setup() {
  pinMode(ledPin, OUTPUT);
  // Timer0 is already used for millis() - we'll just interrupt somewhere
  // in the middle and call the "Compare A" function below
  OCR0A = 0xAF; // TIMER0_COMPA_ value
  TIMSK0 |= _BV(OCIE0A); // enable TIMER0_COMPA_vect ISR
}

void loop() {
}

// Interrupt is called about once a millisecond,
ISR(TIMER0_COMPA_vect)
{
  // This is the main part of BWOD,
  // check to see if it's time to blink the LED; that is, if the difference
  // between the current time and last time you blinked the LED is bigger than
  // the interval at which you want to blink the LED.
  unsigned long currentMillis = millis();

  if (currentMillis - previousMillis >= interval) {
    // save the last time you blinked the LED
    previousMillis += interval; // update timestamp and account for slippage
    //   previousMillis = currentMillis;

    // if the LED is off turn it on and vice-versa:
    if (ledState == LOW) {
      ledState = HIGH;
    } else {
      ledState = LOW;
    }
    // set the LED with the ledState of the variable:
    digitalWrite(ledPin, ledState);
  }
}

Timer0_multitasking - Wokwi ESP32, STM32, Arduino Simulator

[jimLee]

Would this work? Doesn't use interrupts. But then, why? If you don't need 'em.

timedCallback.ino - Wokwi ESP32, STM32, Arduino Simulator