Hi everyone!
As the subject says I'm looking for an easy (maybe also affordable) and effettive way to countdown with my Arduino.
I'm developing an Arduino powered laser tag system. I need my Arduino to count down from 10-20-30 or other minutes. When the timer stops I need my Arduino to do an action like playing a sound and writing data on a lcd display or something similar. At first I taught that using a Rtc module like the ds1307 could do the job but then I realised that it's not a good way to deal with.
I also need to use this timer for scheduling reasons:
Since I need to transmit data from an Arduino to another, via radio transmission (433) and I have to avoid that other Arduino are transmitting at the same time, I taught that using this timer and tell the Arduino to transmit, for example every 2 minutes, could be good.
So... Problem is that I attually don't know how to do this without making my Arduino busy all time. I need it to be ready to receive strings via ir and react with other random events.
Oops I forgot... I'm using an Arduino Mega with AtMega 2560.
Do you guys think it's a programming trick or do you think (like me) that an ic is mandatory (like a timer or? I don't know which one)?
Please I need your advices. All suggestions are accepted.
Thank you
Thanks a lot, guys 
I will try soon both the solutions you posted.
About the i.c. is there a specific i.c. that could do the job and tell the Arduino when it's time to do something? I mean when the time is up.
Thanks again
Hi guys,
first I would like to thank you very much because you gave me the exact type of code I was looking for. They both works like a charm but I decided to use the one from Delta_G since it's lighter and more suitable for me.
Actually I have been trying to develop some functions able to do this kind of things:
- Set a timer when a code is received via 433 MHz (a code that contains the number of minutes that inizialize the timer
- Pause the timer without resetting the countdown
- Add some time (e.g. +5 min, again from a radio code containing the amount of minutes to add)
- reset the timer
I've adapted the code in order to remove things I don't need like hours and days, here it is:
#define SEC_PER_MIN (60)
#define SEC_PER_HOUR (60ul * 60)
unsigned long countdownTime = 0;
void setup(){
Serial.begin(9600);
delay(20);
Serial.println(F("Enter Minutes"));
int minutes = getInputFromUser();
Serial.println(F("Enter Seconds"));
int seconds = getInputFromUser();
countdownTime = seconds + (minutes * SEC_PER_MIN);
}
void loop(){
static unsigned long lastTick = millis();
unsigned long currentMillis = millis();
// Way more accurate timing this way than with delay
// Also allows for code to do other things during countdown
if (currentMillis - lastTick >= 1000){
lastTick += 1000;
countdownTime--;
displayTime(countdownTime);
}
if (countdownTime == 0){
Serial.println(F("Countdown Finished"));
while(1); // infinite loop... lock up program until reset
}
}
// blocks program for input from user via serial
// returns the number entered as an int
int getInputFromUser(){
char buf[5];
int index = 0;
while(Serial.available() < 1); // DO nothing until serial arrives
buf[index] = Serial.read();
while (buf[index] != '\n'){
if(Serial.available()){
buf[++index] = Serial.read();
}
// Don't run over the end of buf
if (index == 4){
buf[index] = '\n';
break;
}
}
// Received a null, Serial transmission is over
return atoi(buf);
}
//Prints time to serial in D:H:M:S format
void displayTime(unsigned long aTime){
int seconds = aTime % SEC_PER_MIN;
int minutes = (aTime % (SEC_PER_HOUR)) / SEC_PER_MIN;
Serial.println(F("tick"));
Serial.print(F(" : "));
Serial.print(minutes);
Serial.print(F(" : "));
Serial.println(seconds);
}
Again, problem is that I don't know how to make my Arduino, using this code, count every X minutes (e.g. 2 minutes) and do a mySwitch.send(code,24); in order to send data every X minutes to the Control Base Arduino. I need to do this timing in order not to have packet collisions since every rifle must send data to the base without interfering with others (I taught that maybe giving a different seconds amount for every rifle should be good).
Here is the code that I'm using to send data via radio (433 MHz), powered by the RcSwitch Library:
/*
Example for different sending methods
http://code.google.com/p/rc-switch/
*/
#include <RCSwitch.h>
RCSwitch mySwitch = RCSwitch();
void setup() {
Serial.begin(9600);
// Transmitter is connected to Arduino Pin #10
mySwitch.enableTransmit(10);
// Optional set pulse length.
// mySwitch.setPulseLength(320);
// Optional set protocol (default is 1, will work for most outlets)
// mySwitch.setProtocol(2);
// Optional set number of transmission repetitions.
// mySwitch.setRepeatTransmit(15);
}
void loop() {
/* Same switch as above, but using decimal code */
mySwitch.send(123456, 24);
}
Could you please tell me the correct way to do these kind of things?
Thanks again, guys.