Please help me program a countdown timer?

hi, don't have lot of experience arduino, make countdown timer can count down in years, days, , hours. have absolutely no idea begin , i'm more willing pay code or hardwiring. needs count down reliably 90 years. ideally done end of week.

i have arduino uno , startup kit comes it, , don't mind buying components think important.

many thanks! i'm in bit of hurry sooner can reply, better! <3 thank

what display countdown on?
how powered?
at point bound lose power - need battery backup thru that?
how long need run for? need account leap years , leap seconds if running long enough, or manually add them when occur.

time part simple enough, count 24 hours , count down day , year needed.

code: [select]


unsigned long currentmicros;
unsigned long previousmicros;
unsigned long elapsedtime;

// initial time start, 10:00:00 90 years, 240 days. (around start of may),
// adjust needed.

// working, more display code if needed

byte hundredths;
byte tenths;
byte secondsones = 0;
byte oldsecondsones;
byte secondstens = 0;
byte minutesones = 0;
byte minutestens = 0;
byte hoursones= 0;
byte hourstens = 1;
int days = 240; //
byte years = 90;

void setup(){

serial.begin(115200); // make serial monitor match
serial.println (setup done");
}

void loop(){

currentmicros = micros();

// how long's been?
elapsedtime = currentmicros - previousmicros;
if ( elapsedtime >=10000ul){  // 0.01 second passed? update timers
previousmicros  = previousmicros + 10000ul;
hundredths = hundredths+1;
if (hundredths == 10){
    hundredths = 0;
    tenths = tenths +1;
    if (tenths == 10){
        tenths = 0;
        secondsones = secondsones + 1;
        if (secondsones == 10){
            secondsones = 0;
            secondstens = secondstens +1;
            if (secondstens == 6){
                secondstens = 0;
                minutesones =  minutesones + 1;
                if (minutesones == 10){
                    minutesones = 0;
                    minutestens = minutestens +1;
                    if (minutestens == 6){
                        minutestens = 0;
                        hoursones = hoursons + 1;
                          if (hoursones == 10){
                              hoursones = 0;
                              hourstens = hourstens +1;
                                if ( (hourstens == 2) && (hoursones == 4){
                                      hoursones = 0;
                                      hourstens = 0;
                                      if (days>1){
                                          days = days-1;
                                           }
                                      else {
                                         days = 365;
                                         years = years - 1;
                                         }                             
                                      } // 24 hr rollover check
                                   } //hourstens rollover check
                              } // hoursones rollover check
                        } // minutestens rollover check
                     } // minutesones rollover check
                 } // secondstens rollover check
              } // secondsones rollover check
          } // tenths rollover check
       } // hundredths rollover check
} // hundredths passing check

if (oldsecondsones != secondsones){  // show elapsed time
oldsecondsones = secondsones;
serial.print (years);
serial.print(":");
serial.print(days);
serial.print(":");
serial.print(hourstens);
serial.print(hoursones);
serial.print(":");
serial.print(minutestens);
serial.print(minutesones);
serial.print(":");
serial.print(secondstens);
serial.println(secondsones);

} // end 1 second check

} // end loop


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