#define relayPin  5
#define trigPin   9
#define echoPin   10
  

    
bool lampIsOn;
  

    
long duration;
int distance;
  

    
int max_dist=30; // cm
int alert_dist=30; // cm

  

    
bool oneDetectionOnly=true;
int stay_time_ms=30; 
long came_time_ms;

#define DIST_FAR            1
#define DIST_CAME           2
#define DIST_NEAR           3
#define DIST_WENT           4
#define DIST_WAIT_2_LEAVE   5

byte currect_dist_state;
bool long_near=false;

  

    
float maxLenInMicroSec=max_dist * 2 / 0.034; 

  

    
void setup() {
  pinMode(trigPin, OUTPUT); 
  pinMode(echoPin, INPUT); 
    pinMode(relayPin, OUTPUT);

    killTheLight();
  currect_dist_state=DIST_FAR;
}
  

    

byte nearCnt=0;
bool handIsNear(){
  dist_state_handler(); 
  return detect_stay();
}
  

    
void loop() {
  if(handIsNear()){
    toggle_light();
  }
  delay(50);
}
  

    

bool detect_stay(){
  bool ret=false;

  if((currect_dist_state==DIST_NEAR) and (long_near == true)){
    ret = true;
    if(oneDetectionOnly){
      currect_dist_state=DIST_WAIT_2_LEAVE;
      long_near=false;
    }
  }
  return ret;

}
  

    

void dist_state_handler() {
  byte nextState;

  calc_dist();

  bool detected=((distance==0)||(distance > alert_dist))?false:true;
  switch(currect_dist_state){
    case DIST_FAR:
                  nextState=(detected)?DIST_CAME:DIST_FAR;
                  break;
    case DIST_CAME:
                  nextState=DIST_FAR;
                  if(detected){
                    nextState=DIST_NEAR;
                    came_time_ms=millis();
                  }
                  break;
    case DIST_NEAR:
                  nextState=(detected)?DIST_NEAR:DIST_WENT;
                  break;
    case DIST_WENT:
                  nextState=DIST_FAR;
                  if(detected){
                    nextState=(oneDetectionOnly)?DIST_WAIT_2_LEAVE:DIST_NEAR;
                  }
                  break;
    case DIST_WAIT_2_LEAVE:
                  nextState=(detected)?DIST_WAIT_2_LEAVE:DIST_WENT;
                  break;
  }
  currect_dist_state=nextState;
}
  

    
void calc_dist(){
  sendTrig();
  duration = pulseIn(echoPin, HIGH,maxLenInMicroSec);
  distance= round(duration*0.034/2); 
}
void sendTrig(){
    // Clears the trigPin
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  // Sets the trigPin on HIGH state for 10 micro seconds
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
}
  

    
void lightTheLamp(){
    digitalWrite(relayPin, HIGH);
    lampIsOn=true;
}
void killTheLight(){
    digitalWrite(relayPin, LOW);
    lampIsOn=false;
}
void toggle_light(){
  if(lampIsOn){
    killTheLight();
  }
  else {
    lightTheLamp();
  }
}