diff --git a/snake_arduino/snake_arduino.ino b/snake_arduino/snake_arduino.ino
index dea8e41..582e30a 100644
--- a/snake_arduino/snake_arduino.ino
+++ b/snake_arduino/snake_arduino.ino
@@ -1,5 +1,10 @@
 #include "Arduino_LED_Matrix.h"
 
+#define BTNUP 13
+#define BTNRIGHT 12
+#define BTNBOTTOM 11
+#define BTNLEFT 10
+
 // create LED matrix object
 ArduinoLEDMatrix matrix;
 
@@ -27,6 +32,7 @@ int snake_y[96]= {3, 3, 3, 3};
 int snake_len= 4;
 
 char direction= 'r';
+// used to avoid a double change direction before LED turns on
 char new_direction= 'r';
 
 int points= 0;
@@ -38,49 +44,20 @@ int apple_y= 4;
 int loop_delay= 300;
 long exec_t2= millis();
 
+
 void setup() {
   //Serial.begin(115200);
   Serial.begin(9600);
   // stard LED matrix
   matrix.begin();
-  // btn up
-  pinMode(13, INPUT_PULLUP);
-  // btn right
-  pinMode(12, INPUT_PULLUP);
-  // btn bottom
-  pinMode(11, INPUT_PULLUP);
-  // btn left
-  pinMode(10, INPUT_PULLUP);
+  pinMode(BTNUP, INPUT_PULLUP);
+  pinMode(BTNRIGHT, INPUT_PULLUP);
+  pinMode(BTNBOTTOM, INPUT_PULLUP);
+  pinMode(BTNLEFT, INPUT_PULLUP);
 
   randomSeed(analogRead(0));
 }
 
-void add_tail_block() {
-  snake_len++;
-  snake_y[snake_len-1]= snake_y[snake_len-2];
-  snake_x[snake_len-1]= snake_x[snake_len-2];
-}
-
-void show_apple() {
-  frame[apple_y][apple_x]= 1;
-}
-
-void eat_apple() {
-  points++;
-  Serial.println(points);
-  // increase difficult each 5 apples
-  if (points % 5 == 0) loop_delay-= 50;
-  
-  // generate new apple coordinates
-  frame[apple_y][apple_x]= 0;
-  apple_x= random(11);
-  apple_y= random(7);
-  show_apple();
-  
-  // increase snake length
-  add_tail_block();
-}
-
 void game_over() {
   // show gameover frame
   matrix.loadFrame(frame_game_over);
@@ -107,15 +84,39 @@ void game_over() {
   while (true) delay(10000);
 }
 
-void move_snake() {
-  int i=0;
 
+void add_tail_block() {
+  snake_len++;
+  snake_y[snake_len-1]= snake_y[snake_len-2];
+  snake_x[snake_len-1]= snake_x[snake_len-2];
+}
+
+void show_apple() {
+  frame[apple_y][apple_x]= 1;
+}
+
+void eat_apple() {
+  points++;
+  Serial.println(points);
+  // increase difficult each 5 apples
+  if (points % 5 == 0) loop_delay= max(50, loop_delay-=50);
+  
+  // generate new apple coordinates
+  frame[apple_y][apple_x]= 0;
+  apple_x= random(11);
+  apple_y= random(7);
+  
+  // increase snake length
+  add_tail_block();
+}
+
+void move_snake() {
   int y= snake_y[snake_len-1];
   int x= snake_x[snake_len-1];
   frame[y][x]= 0;
 
   // move and render the snake tail
-  for (i= snake_len-1; i > 0; i--) {
+  for (int i= snake_len-1; i > 0; i--) {
     frame[snake_y[i-1]][snake_x[i-1]]= 1;
     if (snake_x[0] == snake_x[i] && snake_y[0] == snake_y[i])
       game_over();
@@ -145,21 +146,18 @@ void move_snake() {
     snake_y[0]-= 1;
     if (snake_y[0] < 0) snake_y[0]= 7;
   }
-  if (snake_y[0] == apple_y && snake_x[0] == apple_x) eat_apple();
+  if (snake_y[0] == apple_y && snake_x[0] == apple_x)
+    eat_apple();
 
   // render the snake head
   frame[snake_y[0]][snake_x[0]]= 1;
 }
 
 void change_direction() {
-  // up
-  int u= digitalRead(13);
-  // right
-  int r= digitalRead(12);
-  // bottom
-  int b= digitalRead(11);
-  // left
-  int l= digitalRead(10);
+  int u= digitalRead(BTNUP);
+  int r= digitalRead(BTNRIGHT);
+  int b= digitalRead(BTNBOTTOM);
+  int l= digitalRead(BTNLEFT);
   
   if      (u == LOW && direction != 'b') new_direction= 'u';
   else if (r == LOW && direction != 'l') new_direction= 'r';