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[on:]

It'll be great if you could advice me on which arduino software solution (timer, interrupt, alarm, millis,...) and sketch structure to use to schedule the following (on Arduino Mega):
each day, starting at 7 o'clock in the morning and ending at 10 o'clock at night,
to sense every 5 minutes the status of 8 switches and display the result ("X" switch on 8 have the status "On").
Great thanks in advance for your kind help.

[Reply #1 on:]

The Arduino clock (millis(), etc) will drift over time.  If you don't mind resetting the time every week or so it might be a usable solution.  Otherwise you will want an external clock.

[Reply #2 on:]

Something simple like this should work.  Let me know if you can't follow it. Needs some cleanup (;s) and flesh out the sensors you read, but the flow is pretty clear.

Code:

unsigned long current_millis = 0;
unsigned long previous_millis = 0;
unsigned long elapsed_millis = 0;
unsigned long interval = 300000UL; // 5 x 60 seconds x 1000mS
end_of_day = 0; //  180 = 15 hrs x 12 five minute intervals
morning = 0; // 108 = 9 hours x 12 five minute intervals
interval_type = 0; // 0 = day,1=night
void setup(){
define I/O pins
{ wait for button press to sync time to 7:00 for very first start, or after a restart}
current_millis = millis()
previous_millis = current_millis();
}
void loop(){
elapsed_millis = current_millis - previous_millis  
if (elapsed_millis >= interval && interval_type = 0 ){
read the 8 switches
display the results
end_of_day = end_of_day + 1;
if (end_of_day == 180){
end_of_day = 0
interval_type = 1
}
}
if(elapsed_millis >=interval && interval_type == 1){
end_of_night = end_of_night +1
if (end_of_night == 108){
end_of_night = 0
interval_type = 0
}
}
}

[Reply #3 on:]

You could do a search for "event manager" or "event scheduler" that was posted recently and see how hard it would be to schedule 180 events. I think the approach above is pretty straightforward tho.

[Reply #4 on:]

Looks like I forgot to set
previous_millis = current_millis;
after the interval passed, you'll need to add that in.

[Reply #5 on:]

Thanks a lot for your very fast reply.
I have to test your solution and enlarge search following your advices.
Is that a solution combining alarm and timer could be an effective alternative possible?
if yes, how to start function and stop it, containing timer ?
To be more precise it should be noted that the sketch will run all over the year and must be stable every days of the weeks.   

[Reply #6 on:]

You are certainly able to add some more buttons and a display to show the time, an indicator that a reading is taking place, etc.
Start with the  basics, build up from there.

[Reply #7 on:]

I beg your pardon, but as i'm novice, could you please give me more details about the following part and how to do that:
"{ wait for button press to sync time to 7:00 for very first start, or after a restart}"

Great thanks.

[Reply #8 on:]

On other hand, what do you think of using an external real time clock hardware (like DS1307 that i've discovered) ? Is it easier to implement and use? Is it reliable? Do you have code examples of using that type of real time clock hardware to schedule events ?

[Reply #9 on:]

http://combustory.com/wiki/index.php/RTC1307_-_Real_Time_Clock

and a lot of links with : http://arduino.cc/playground/Main/InterfacingWithHardware

look in the "TIME" section.

[Reply #10 on:]

Great thanks for your kind and fast reply !