#define led_pin 2
#define chave_pin 21
unsigned char sinal_chave ;

void setup() {
pinMode(led_pin, OUTPUT);
pinMode(chave_pin, INPUT);
}
void loop() 
{
sinal_chave = digitalRead(chave_pin);
if (!sinal_chave){
digitalWrite(led_pin , HIGH);
}
else{
digitalWrite(led_pin, LOW);  
}

  delay(100); // this speeds up the simulation
}