bttn.ino

const int in = 1,
          out = 3;
boolean on = false,
        switchable = true;
void setup() {
  pinMode(in, INPUT);
  pinMode(out,OUTPUT);
}

void loop(){
  if(digitalRead(in)==LOW && switchable == true){
    if(on)on = false;
    else on = true;
    switchable = false;
    if(on) analogWrite(out,200);
    else analogWrite(out,0);
  }
  else if(digitalRead(in)==HIGH){
    switchable = true;
  }
}

Read about the project here