Simple Countdown timer using Duemilanove

Using Arduino Project Guidance
1

Hi there,

Gotta say im completely new to the whole programming thing, so bear with me.

What im after is to program an arduino duemilanove to countdown from around 2 hours, and when it reaches the end, it will trigger a piezo siren that i have attached to it.
I know it most probably pretty easy for some of you, but for the complete novice, im outta my depth. I had a friend mention something about using a high side driver, or something like that??

I appreciated any help that i can get.

Thanks

2

Check - Arduino Playground - StopWatchClass -

Although a stopwatch counts up it becomes fairly easy to add a few lines to do a countdown

pseudocode

long t = 2 * 60 * 60 * 1000L;   // 2 hours
loop()
{
if t - stopwatchtime < 0 ==> buZZ!!!
}
3

Right thanks for that, ill look into it. Im really struggling with the whole programming piece, essentially i want the easiest way to countdown from 2 hours, and set off a buzzer at that point.
Dont need to display anything,

what stopping me from using a delay(7200000) two hours (similar to the blink) and then telling the pin to go high??

Thanks

4

what stopping me from using a delay(7200000) two hours (similar to the blink) and then telling the pin to go high??

think nothing, but how long should the pin be HIGH?

delay(7200000UL); // add the UL for Unsigned Long

better

delay(2 * 60 * 60 * 1000UL); // shows better that it is 2 hours...

5