Fan needs to run every two hours

Projects Programming
1

Hi,

I am working on a greenhouse project. During winter the ventilation louvres will be closed all the time and this wil cause stale air inside the greenhouse.
I want to write a piece of code that operates a ventilation fan every two hours for about 15 seconds to expel stale air.
I have been racking my brain and watched several YouTube clips and tutorials and I came up with the idea to use an interrupt that runs independent of the main program. the interrupt is triggered by one of the internal timers.
My problem is that I don't know how to set up an internal timer and an interrupt that happens every two hours.
Could somebody please help to point into the right direction or provide a bit of basic code that shows how to do this?
In a future stage I will add a RTC (Real time clock) to the board. I know this is complete overkill but I want to use the clock function for other things as well which need to be more precise (Such as draining growbeds).
Many thanks in advance for your input.

2

Hello and welcome :slight_smile:

I never use interrupts, I prefer polling with millis(), something like this will turn on the onboard led for one second, then off for 3 seconds and repeat:

const uint8_t ledPin = 13;
const uint32_t
  timeON  = 1000ul,
  timeOFF = 3000ul;

bool ledState = false;
uint32_t
  time     = timeOFF,
  curTime  = 0,
  prevTime = 0;


void setup()
{
  pinMode( ledPin, OUTPUT );
}

void loop()
{
  curTime = millis();

  if ( curTime - prevTime >= time )
  {
    prevTime = curTime;
    ledState = !ledState;
    time = ledState ? timeON : timeOFF;
    digitalWrite( ledPin, ledState );
  }
}
3

Hi Guix,

Thank you very much for this compact and simple sketch.
I never thought about it like that.
Initially I thought using an interrupt wouldn't make a difference on the loop and that's why I was looking into that direction.
Your code is simple and doesn't cause much delay in the program.
I will play around with it.
I think it will exactly do what I wanted to achieve. So, thank you very much for your help!

Luc