int ledpin=3;
int buttonpin=12;
int ledstate=0;
int buttonnew;
int buttonold=1;
int dt=500;
void setup() {
  // put your setup code here, to run once:
Serial.begin(9600);
pinMode(buttonpin, INPUT);
pinMode(ledpin, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
buttonnew=digitalRead(buttonpin);
if (buttonold==0 && buttonnew==1){
 if (ledstate==0){
digitalWrite(ledpin, HIGH);
ledstate=1;
}

else{
digitalWrite(ledpin,LOW);
ledstate=0;
}
}
buttonold=buttonnew;
delay(dt);
}