 #define PIN_LDR_DOWN  1 // PC1
 #define PIN_LDR_LEFT  2 // PC2
 #define PIN_LDR_RIGHT 3 // PC3
-#define THRESHOLD_LDR_VIRT 20
-#define THRESHOLD_LDR_HORZ 20
+#define THRESHOLD_LDR_VIRT 25
+#define THRESHOLD_LDR_HORZ 25
 
 #define SERVO_PIN_VIRT 8 // PB0
 #define SERVO_PIN_HORZ 9 // PB1

    
    servo_virt.attach(SERVO_PIN_VIRT);
    servo_horz.attach(SERVO_PIN_HORZ);
}

void loop()


void tkr_move()
{
    int diff_virt = tkr_diff_virt();
    int diff_horz = tkr_diff_horz();
    Serial.println(); 
    
    if (diff_virt) {
      // move up or down
      int deg = servo_virt.read();
      
      if (diff_virt > 0) {
        ++deg;
        if (deg > 160) deg = 160;
      } else {
        --deg;
        if (deg < 40) deg = 40;
      }
      
      Serial.print(diff_virt);
      Serial.print('-');
      Serial.println(deg); 
      
      // move a degree each loop until target is reached.
      servo_virt.attach(SERVO_PIN_VIRT);
      servo_virt.write(deg);
      
    }

    if (diff_horz) {
      // move left or right.
      int deg = servo_horz.read();
      
      if (diff_horz > 0) {
        ++deg;
        if (deg > 170) deg = 170;
      } else {
        --deg;
        if (deg < 10) deg = 10;
      }
      
      Serial.print(diff_horz);
      Serial.print('-');
      Serial.println(deg); 
      
      // move a degree each loop until target is reached.
      servo_horz.attach(SERVO_PIN_HORZ);
      servo_horz.write(deg);
      
    }
    
}

int tkr_diff_virt()
{
    int up = analogRead(PIN_LDR_UP);
    int down = analogRead(PIN_LDR_DOWN);
