int LED1 = 3;
int PB_1 = 2;

void setup() {
  pinMode(LED1, OUTPUT);
  pinMode(PB_1, INPUT_PULLUP);

}

void loop() {
  if (digitalRead(PB_1) == LOW)
{
  digitalWrite(LED1, HIGH);
}
else
{
  digitalWrite(LED1, LOW);
}
}