refactor: Remove magic numbers in ScienceLab.temperature

pslab/sciencelab.py

@@ -8,8 +8,9 @@
 from __future__ import annotations
 
 import time
-from typing import Iterable, List
+from typing import Dict, Iterable, List, Tuple
 
+import numpy as np
 import pslab.protocol as CP
 from pslab.connection import ConnectionHandler, SerialHandler, autoconnect
 from pslab.instrument.logic_analyzer import LogicAnalyzer
@@ -44,21 +45,57 @@ def __init__(self, device: ConnectionHandler | None = None):
         self.multimeter = Multimeter(device=self.device)
         self.power_supply = PowerSupply(device=self.device)
 
+    # Calibration parameters for CTMU temperature measurement
+    # Format: {current_range_index: (offset_mV, slope)}
+    _CTMU_TEMPERATURE_CALIBRATION: Dict[int, Tuple[float, float]] = {
+        1: (646, 1.92),
+        2: (701.5, 1.74),
+        3: (760, 1.56),
+    }
+
+    # CTMU ADC channel used for internal temperature sensor
+    _CTMU_CHANNEL_TEMPERATURE = 0b11110
+
+    # Unit conversion factor
+    _VOLTS_TO_MILLIVOLTS = 1000
+
+    # Minimum valid CTMU voltage before switching current range (Volts)
+    _MIN_CTMU_VOLTAGE = 0.3
+
     @property
-    def temperature(self):
-        """float: Temperature of the MCU in degrees Celsius."""
-        # TODO: Get rid of magic numbers.
-        cs = 3
-        V = self._get_ctmu_voltage(0b11110, cs, 0)
-
-        if cs == 1:
-            return (646 - V * 1000) / 1.92  # current source = 1
-        elif cs == 2:
-            return (701.5 - V * 1000) / 1.74  # current source = 2
-        elif cs == 3:
-            return (760 - V * 1000) / 1.56  # current source = 3
-
-    def _get_ctmu_voltage(self, channel: int, current_range: int, tgen: bool = True):
+    def temperature(self) -> float:
+        """Get the temperature of the MCU."""
+        # CTMU current range index (higher index = higher current)
+        current_range = 3
+
+        V = self._get_ctmu_voltage(
+            self._CTMU_CHANNEL_TEMPERATURE,
+            current_range,
+            0,
+        )
+
+        # If the voltage is too low, we might be using a too high current source
+        # range. Try to lower the range until we get a reasonable voltage.
+        while V < self._MIN_CTMU_VOLTAGE and current_range > 1:
+            current_range -= 1
+            V = self._get_ctmu_voltage(
+                self._CTMU_CHANNEL_TEMPERATURE,
+                current_range,
+                0,
+            )
+
+        try:
+            offset, slope = self._CTMU_TEMPERATURE_CALIBRATION[current_range]
+        except KeyError as exc:
+            raise ValueError(
+                f"Unsupported CTMU current range: {current_range}"
+            ) from exc
+
+        return (offset - V * self._VOLTS_TO_MILLIVOLTS) / slope
+
+    def _get_ctmu_voltage(
+        self, channel: int, current_range: int, tgen: bool = True
+    ) -> float:
         """Control the Charge Time Measurement Unit (CTMU).
 
         ctmu_voltage(5, 2) will activate a constant current source of 5.5 µA on