Timer?

anybody can help?
i'm trying program timer function on button hold relay.
so when push button, relay should hold for, 3 seconds , release.
i not want use delay(); because nead other things while program runs!

code: [select]


#define relaypin 9
#define buttonpin 10

void setup()
{
pinmode(relaypin,output);
pinmode(buttonpin,input_pullup);
}

unsigned long triggertime=0;
void loop()
{
unsigned long t=millis();

//assume relay active low
//(most are)
if ((t-triggertime) > 3000)
  digitalwrite(relaypin,high);

if ( digitalread(buttonpin)==low)
  {
  triggertime=t;
  digitalwrite(relaypin,low);
  }
}


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