       Serial.print("-");
       Serial.println(servo_horz_pos); 
       
-      // move a degree each loop until target is reached.
-      //servo_horz.attach(SERVO_PIN_HORZ);
+      // move a bit each loop until target is reached.
       servo_horz.writeMicroseconds(servo_horz_pos);
       
     }
     
-}
-
-int tkr_diff_virt()
-{
-    int up = analogRead(PIN_LDR_UP);
-    int down = analogRead(PIN_LDR_DOWN);
-
-    /*
-    Serial.print(up); 
-    Serial.print(":");
-    Serial.print(down); 
-    Serial.print(":");
-    */
-    
-    int diff = up - down;
-    if (abs(diff) > THRESHOLD_LDR_VIRT) {
-      return diff;
-    }
-    
-    return 0;
 }
 
 int tkr_diff_horz()


void tkr_move()
{
    int diff_virt = tkr_diff_virt();
    int diff_horz = tkr_diff_horz();
    //Serial.println(); 
    
    if (diff_virt) {
      // move up or down

      if (diff_virt > 0) {
        servo_virt_pos += SERVO_INCREMENT;
        if (servo_virt_pos > SERVO_VIRT_MAX) servo_virt_pos = SERVO_VIRT_MAX;
      } else {
        servo_virt_pos -= SERVO_INCREMENT;
        if (servo_virt_pos < SERVO_VIRT_MIN) servo_virt_pos = SERVO_VIRT_MIN;
      }
      
      Serial.print("V > ");
      Serial.print(diff_virt);
      Serial.print('-');
      Serial.println(servo_virt_pos); 
      
      // move a degree each loop until target is reached.
      //servo_virt.attach(SERVO_PIN_VIRT);
      servo_virt.writeMicroseconds(servo_virt_pos);
      
    }

    if (diff_horz) {
      // move left or right.

#define LED_DEBUG 13
#define PIN_TX 7

#define PIN_LDR_LEFT  2 // PC2
#define PIN_LDR_RIGHT 3 // PC3
#define THRESHOLD_LDR_HORZ 50
#define MOVE_INTERVAL_MILLIS 60

#define SERVO_INCREMENT 5 // How much to move each loop
#define SERVO_PIN_HORZ 8 // PB1
#define SERVO_HORZ_MAX 2800
#define SERVO_HORZ_MIN 700


#define I2C_SLAVE_ADDR 100

