diff --git a/src/main.cpp b/src/main.cpp
index 675b1d6..6537301 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -4,15 +4,15 @@
 #define MIDI_NAME {'P', 'i', 'n', 'g', 'b', 'o', 'a', 'r', 'd'}
 #define MIDI_NAME_LEN 9
 
-#define CHECK_PINS 9
+#define KEY_GROUP_NUM 9
 #define KEY_PINS 6
+#define NUMBER_OF_KEYS 49
 #define BOUNCE_TIME 5
 #define POWER_SUPPLY_CHECK_PIN 13
 
-#define NUMBER_OF_KEYS 49
 #define SELF_DRIVE_INTERVAL 100
 
-Bounce check_pins[CHECK_PINS] {
+Bounce group_pins[KEY_GROUP_NUM] {
   {14, BOUNCE_TIME}, // not KEYS1..6
   {15, BOUNCE_TIME}, // not KEYS7..12
   {16, BOUNCE_TIME}, // not KEYS13..18
@@ -25,20 +25,20 @@ Bounce check_pins[CHECK_PINS] {
 };
 
 // not KEY0%6..not KEY5%6
-const unsigned char key_pins[KEY_PINS] {2, 3, 4, 5, 6, 7};
+const uint8_t key_pins[KEY_PINS] {2, 3, 4, 5, 6, 7};
 // Array of pressed keys (initially all 0)
 bool keys_pressed[NUMBER_OF_KEYS];
 // K1, K2, K3, K4, K5, K12, K13, K14, K15
-const unsigned char self_drive_pins[CHECK_PINS] {8, 9, 10, 11, 12, 26, 23, 24, 25};
-volatile unsigned char curr_self_drive_pin = 0;
+const uint8_t self_drive_pins[KEY_GROUP_NUM] {8, 9, 10, 11, 12, 26, 23, 24, 25};
+volatile uint8_t current_self_drive_pin = 0;
 IntervalTimer self_drive_timer = IntervalTimer();
 
 // Map the current array and pressed key to a MIDI note
-unsigned char mapToMidi(char curr_arr, char key) {
-  unsigned char offset = (curr_arr >> 1) * 12;
+uint8_t mapToMidi(uint8_t active_key_group, uint8_t key) {
+  uint8_t offset = (active_key_group >> 1) * 12;
   // TODO: maybe we have to switch the notes and array offsets
   // Uneven offset are the upper octave, even the lower
-  if (curr_arr & 1) {
+  if (active_key_group & 1) {
     switch (key) {
       case 0: return offset + 42; // F#2 + offset
       case 1: return offset + 43; // G2 + offset
@@ -63,18 +63,18 @@ unsigned char mapToMidi(char curr_arr, char key) {
 }
 
 // Check if any of the array pins fell since last time
-char findCurrentArrPin() {
-  for (unsigned char i = 0; i < CHECK_PINS; i++) {
+int8_t getActiveKeyGroup() {
+  for (uint8_t i = 0; i < KEY_GROUP_NUM; i++) {
     // Update status
-    check_pins[i].update();
+    group_pins[i].update();
     // Check if the pin fell or is low
     // ! inverted
-    if (check_pins[i].fell()) return i;
+    if (group_pins[i].fell()) return i;
   }
 
   // If none fell we should have enough time to see which one is low
-  for (unsigned char i = 0; i < CHECK_PINS; i++) {
-    if (check_pins[i].read() == LOW) return i;
+  for (uint8_t i = 0; i < KEY_GROUP_NUM; i++) {
+    if (group_pins[i].read() == LOW) return i;
   }
 
   // Default return
@@ -84,17 +84,17 @@ char findCurrentArrPin() {
 // Set the next self drive pin
 FASTRUN void nextSelfDrivePin() {
   // Set the current pin to high
-  digitalWriteFast(self_drive_pins[curr_self_drive_pin], HIGH);
+  digitalWriteFast(self_drive_pins[current_self_drive_pin], HIGH);
   // Set the next pin
-  curr_self_drive_pin = (curr_self_drive_pin + 1) % CHECK_PINS;
+  current_self_drive_pin = (current_self_drive_pin + 1) % KEY_GROUP_NUM;
 }
 
 // Interrupt for power supply check
 FASTRUN void powerStateChanged() {
-  unsigned char state = digitalReadFast(POWER_SUPPLY_CHECK_PIN);
+  uint8_t state = digitalReadFast(POWER_SUPPLY_CHECK_PIN);
   // ! inverted
   if (state == LOW) {
-    curr_self_drive_pin = 0;
+    current_self_drive_pin = 0;
     self_drive_timer.begin(nextSelfDrivePin, SELF_DRIVE_INTERVAL);
   } else {
     self_drive_timer.end();
@@ -104,11 +104,11 @@ FASTRUN void powerStateChanged() {
 // Initial start function
 void setup() {
   // Set all in- and outputs
-  for (unsigned char i = 0; i < CHECK_PINS; i++) {
-    pinMode(check_pins[i].getPin(), INPUT);
+  for (uint8_t i = 0; i < KEY_GROUP_NUM; i++) {
+    pinMode(group_pins[i].getPin(), INPUT);
     pinMode(self_drive_pins[i], INPUT);
   }
-  for (unsigned char i = 0; i < KEY_PINS; i++) {
+  for (uint8_t i = 0; i < KEY_PINS; i++) {
     pinMode(key_pins[i], INPUT);
   }
   pinMode(POWER_SUPPLY_CHECK_PIN, INPUT);
@@ -121,32 +121,32 @@ void setup() {
 // Main loop
 void loop() {
   // Find active arr pin
-  char curr_arr = findCurrentArrPin();  
+  int8_t active_key_group = getActiveKeyGroup();  
 
   // If none is active, we do nothing, else we check the keys
-  if (curr_arr >= 0) {
+  if (active_key_group >= 0) {
     // Get all the key values ans send the MIDI message if needed
-    unsigned char value;
+    uint8_t value;
     
-    for (unsigned char i = 0; i < KEY_PINS; i++) {
+    for (uint8_t i = 0; i < KEY_PINS; i++) {
       value = digitalReadFast(key_pins[i]);
       // If the key is pressed, we send a MIDI message and set the entry in the array
       // ! inverted
       if (value == LOW) { 
         // Check if the key is not already pressed
-        if (keys_pressed[curr_arr * 6 + i] == 0) {
+        if (keys_pressed[active_key_group * 6 + i] == 0) {
           // Send MIDI message
-          usbMIDI.sendNoteOn(mapToMidi(curr_arr, i), 127, 1);
+          usbMIDI.sendNoteOn(mapToMidi(active_key_group, i), 127, 1);
           // Set the entry in the array
-          keys_pressed[curr_arr * 6 + i] = 1;
+          keys_pressed[active_key_group * 6 + i] = 1;
         }
       } else {
         // Check if the key is not already released
-        if (keys_pressed[curr_arr * 6 + i] == 1) {
+        if (keys_pressed[active_key_group * 6 + i] == 1) {
           // Send MIDI message
-          usbMIDI.sendNoteOff(mapToMidi(curr_arr, i), 0, 1);
+          usbMIDI.sendNoteOff(mapToMidi(active_key_group, i), 0, 1);
           // Set the entry in the array
-          keys_pressed[curr_arr * 6 + i] = 0;
+          keys_pressed[active_key_group * 6 + i] = 0;
         }
       }
     }