Chapter 11 code changes - async and bluetooth

ch-11/_test_encoder_output/pid_controller.py

@@ -0,0 +1,20 @@
+class PIDController:
+    def __init__(self, kp, ki, kd, d_filter_gain=0.1):
+        self.kp = kp
+        self.ki = ki
+        self.kd = kd
+        self.d_filter_gain = d_filter_gain
+
+        self.integral = 0
+        self.error_prev = 0
+        self.derivative = 0
+
+    def calculate(self, error, dt):
+        self.integral += error * dt
+
+        # Add a low pass filter to the difference
+        difference = (error - self.error_prev) * self.d_filter_gain
+        self.error_prev += difference
+        self.derivative = difference / dt
+
+        return self.kp * error + self.ki * self.integral + self.kd * self.derivative