// GLAVNI ARDUINO
        int a = Serial.read();

        display.setCursor(SCR_SPEED_X, SCR_SPEED_Y);
        display.setTextSize(1);
        display.print(a);

        // UPDATE THE TAHOMETER
        display.fillRect(SCR_BRAKE_X, SCR_BRAKE_Y, SCR_BRAKE_W, 64, WHITE);
        display.fillRect(SCR_BRAKE_X, SCR_BRAKE_Y, SCR_BRAKE_W, 64 - map(a, 0, 150, 0, 64), BLACK);

        refreshScreen = true;



// SPOREDNI ARDUINO

// PINS
#define PIN_RPM_SENSOR                                                          3 // INTERRUPT PIN! DO NOT CHANGE IT!!


// GLOBAL VARIABLES
volatile uint32_t revDuration                   =                               60000;
volatile uint32_t revTick                       =                               0;


void revolution()
{
    revDuration = millis() - revTick;
    revTick = millis();
}


void setup()
{
    Serial.begin(9600);

    pinMode(PIN_RPM_SENSOR, INPUT);
    attachInterrupt(digitalPinToInterrupt(PIN_RPM_SENSOR), revolution, RISING); // INTERRUPT PIN 3
}


void loop()
{
   Serial.write(60000 / revDuration);

    delay(500);
}