Make car mass configurable at runtime

Replace the compile‑time CAR_MASS constant with a runtime‑settable
_member _carMass. Add Engine::setCarMass, default it to 1200 kg, and
use it in the acceleration calculation. Prompt the user for the
car mass on startup via Serial and update the enable/disable messages.

Engine.cpp

@@ -33,7 +33,7 @@ void Engine::update(float dt, uint8_t gearIdx) {
   const float dragForce = 0.5f * DRAG_COEFF * FRONTAL_AREA * (_speedMs * _speedMs);
   const int direction = (gearIdx == -1) ? -1 : 1;
   const float netForce = direction * engineForce - brakeForce - dragForce;
-  const float acceleration = netForce / CAR_MASS;
+  const float acceleration = netForce / _carMass;
 
   _speedMs += acceleration * dt;
   if (_speedMs < 0.0f) _speedMs = 0.0f;

Engine.h

@@ -13,7 +13,6 @@ constexpr float GEAR_RATIO[6] = {
 
 constexpr float FINAL_DRIVE = 3.74f;   // przekładnia różnicowa
 constexpr float WHEEL_RADIUS = 0.30f;  // m
-constexpr float CAR_MASS = 1200.0f;    // kg
 constexpr float RPM_IDLE = 800.0f;     // obroty jałowe
 constexpr float RPM_MAX = 7000.0f;     // maksymalne obroty
 
@@ -31,6 +30,8 @@ public:
 
   void begin();
 
+  void setCarMass(float mass) { _carMass = mass; }
+
   void update(float dt, uint8_t gearIdx);
 
   int getRPM() const;
@@ -46,6 +47,7 @@ private:
 
   float _engineRPM = EngineConsts::RPM_IDLE;
   float _speedMs = 0.0f;
+  float _carMass = 1200.0f;
 
   float readNormalized(uint8_t pin) const;
 };

Projekt_Arduino.ino

@@ -21,6 +21,29 @@ bool seatBelts = false;
 void setup() {
   Serial.begin(9600);
 
+    // -----------------------------------------------------------------
+    // 1. Ask the user for the car mass (kg) via the Serial monitor.
+    //    We block only until a valid number is received – this is OK
+    //    because it happens once at startup.
+    // -----------------------------------------------------------------
+    Serial.println(F("Enter car mass in kg (e.g. 1200):"));
+    while (true) {
+      // Wait until something is typed
+      if (Serial.available() > 0) {
+        float mass = Serial.parseFloat();          // reads the number
+        if (mass > 0) {                            // basic sanity check
+          engine.setCarMass(mass);
+          Serial.print(F("Car mass set to "));
+          Serial.print(mass);
+          Serial.println(F(" kg"));
+          break;
+        } else {
+          Serial.println(F("Invalid value – try again:"));
+        }
+      }
+    }
+
+
   pinMode(IN_1, OUTPUT);
   pinMode(IN_2, OUTPUT);
   pinMode(ENA_1, OUTPUT);
@@ -41,8 +64,12 @@ void loop() {
 
   if (rfid.check() && rfid.matches(AUTH_UID, AUTH_UID_SIZE)) {
     carEnabled = !carEnabled;
-    Serial.print("Auto działa: ");
-    Serial.println(carEnabled);
+
+    if (carEnabled)
+      Serial.println("Uruchamiam auto");
+    else
+      Serial.println("Gaszę auto");
+
     display.startOrEnd(carEnabled);
   };