Pin change interrupt does not work properly to wake up arduino from sleep mode

Question

I am building a timer circuit using Arduino Pro Mini Atmega168p 5v 16MHz (which later supposed to be become to adjustable one).

Here is the current breadboard view.

(I am supposed to use SS relay at place of that green thing. I am not sure if that item is correct SS relay in Fritzing)

Here is the program code I wrote.

#include <PinChangeInterrupt.h>
#include <PinChangeInterruptBoards.h>
#include <PinChangeInterruptPins.h>
#include <PinChangeInterruptSettings.h>

#include <avr/sleep.h>

// LED to indicate timer is active.
const int ON_LED = 5;
// It should be high when timer is active.
// Connect to relay.
const int PUMP_SWITCH = 6;

// Button to start timer running.
const int START_BUTTON = 8;
// Button to stop timer forcefully.
const int STOP_BUTTON = 9;

volatile boolean timer_running;
volatile int timer_start_time;

// TODO: Make it volatile once timer has mdified as configurable.
volatile unsigned long timer_time = 0;

void enter_sleep_mode() {
  set_sleep_mode(SLEEP_MODE_PWR_DOWN);
  sleep_enable();
  sei();
  sleep_mode();
}

/**
 * Activate timer.
 */
void start_timer() {
  if (!timer_running) {
    // Time period in milliseconds.
    timer_time = 30000ul; // 30 seconds

    timer_running = true;
    timer_start_time = millis();
  }
}

/**
 * Stop timer.
 */
void stop_timer() {
  timer_running = false;
  timer_start_time = 0;
}

void setup() {
  timer_running = false;
  timer_start_time = 0;

  // Configure output pins.
  pinMode(ON_LED, OUTPUT);
  pinMode(PUMP_SWITCH, OUTPUT);

  // Configure pins for input push buttons.
  pinMode(START_BUTTON, INPUT_PULLUP);
  pinMode(STOP_BUTTON, INPUT_PULLUP);

  // Attach interrupt handlers
  // Buttons are with pull up resistors so listening for 'falling' (voltage).
  attachPCINT(digitalPinToPCINT(START_BUTTON), start_timer, FALLING);
  attachPCINT(digitalPinToPCINT(STOP_BUTTON), stop_timer, FALLING);
}

void loop() {
  if (timer_running) {
    digitalWrite(ON_LED, HIGH);
    digitalWrite(PUMP_SWITCH, HIGH);
    // TODO: Handle the case when return value of millis() goes back to start from zero
    if ( (millis() - timer_start_time) >= timer_time ) {
      // Timer elapsed the required time period.
      // So, stop the timer.
      stop_timer();
    }
  }
  else {
    digitalWrite(ON_LED, LOW);
    digitalWrite(PUMP_SWITCH, LOW);
    // Nothing to do If timer is not running.
    // Save power!!
    enter_sleep_mode();

    sleep_disable();
  }
}

The problem is timer does not work when pressing START button starting from third click. Two initial clicks works OK and timer functions as it should be. I think it does not wake up properly from sleep mode. However, wondering why it works for two initial clicks??

Please help me to identify the problem. I don't have much experience in writing Arduino code.

Thanks

Answer 1

Start by checking your calculation of time limits. I see you are mixing signed and unsigned arithmetics - not a very good idea. Check the blink-without-delay example for how to do that.

The declaration of timer_start_time should be paid special attention.

Good luck with your project!

Answer 2

Please help me to identify the problem.

it is always very easy to solve this type of problems, if you just follow some common sense.

1) decompose your functionality into manageable blocks. for example, one is PCINT - can you blink an led with it - and another is going into sleep - can you put the mcu into sleep - and the next is to walk up from sleep - does your mcu support that? what has to be true for that to happen? ...

2) test individual blocks on their own.

3) integrate them into one functional program.

don't co-mingle them day 1. tackle only what you can manage. no more and no less.