add PID

src/pid.h

@@ -0,0 +1,25 @@
+#ifndef PID_CONTROLLER_H
+#define PID_CONTROLLER_H
+
+class PIDController
+{
+private:
+    double kp, ki, kd, setpoint, integral, prev_error;
+    double max_output, min_output, integral_max, dt;
+    bool first_run;
+
+    // Clamp function (C++11 compatible)
+    double clamp(double value, double min_val, double max_val) const;
+
+public:
+    PIDController(double Kp, double Ki, double Kd,
+                  double max_out = 100.0, double min_out = 0.0,
+                  double integ_max = 50.0);
+
+    void setSetpoint(double sp);
+    void setDt(double sample_time);
+    double compute(double current_temp);
+    void reset();
+};
+
+#endif