Temperature control method changed to non-linear PID.

limoControl/puppeteer/_core.py

@@ -377,11 +377,9 @@ class SetupDevice:
             and therefore allows the rest of the program to carry on whilst
             monitoring the temperature.
             
-            The mechanism whereby temperature is regulate is simple: turn heater
-            unit ON or OFF whenever the average temperature is below or above  
-            `target_temperature`.
-            
-            .. TODO:: Implement a more sophisticated algorithm.
+            The temperature is controlled through a PID controller. Heating
+            intensity is defined by the ratio between `current_temperature' and
+            `target_temperature'. If the ratio is above 1, heating stops.
             
             Parameters
             ----------
@@ -406,13 +404,14 @@ class SetupDevice:
             if stop_flag.is_set():
                 break
             
-            # If current_temperature < target_temperature, heat up.
-            if current_temperature.mean() < target_temperature - TEMPERATURE_TOLERANCE:
-                self._heater.set_PWM_dutycycle(self._HEATER_PIN, MAX_POWER)
-            elif  target_temperature - TEMPERATURE_TOLERANCE <= current_temperature.mean() < target_temperature:
-                self._heater.set_PWM_dutycycle(self._HEATER_PIN, int(MAX_POWER*0.7))
+            temperature_ratio = current_temperature.mean() / target_temperature
+            if temperature_ratio <= 1:
+                MOD_POWER = MAX_POWER * (1 - temperature_ratio)**0.125
             else:
-                self._heater.set_PWM_dutycycle(self._HEATER_PIN, 0)
+                MOD_POWER = 0
+            self._heater.set_PWM_dutycycle(self._HEATER_PIN, int(MOD_POWER))
+
+            # Update temperature values.
             temperature = self.report_temperature()
             current_temperature = np.array(temperature)
             t.sleep(1+TEMPERATURE_SAMPLING_FREQ)