Weather battery temperature compensation

enviro/boards/weather.py

@@ -3,7 +3,7 @@
 from breakout_ltr559 import BreakoutLTR559
 from machine import Pin, PWM
 from pimoroni import Analog
-from enviro import i2c, activity_led
+from enviro import i2c, activity_led, config
 import enviro.helpers as helpers
 from phew import logging
 from enviro.constants import WAKE_REASON_RTC_ALARM, WAKE_REASON_BUTTON_PRESS
@@ -190,10 +190,29 @@ def get_sensor_readings(seconds_since_last, is_usb_power):
   ltr_data = ltr559.get_reading()
   rain, rain_per_second = rainfall(seconds_since_last)
 
+  temperature = bme280_data[0]
+  humidity = bme280_data[2]
+
+  # Compensate for additional heating when on different power sources - this
+  # also changes the relative humidity value
+  logging.info(f"  - recorded temperature: {temperature}")
+  logging.info(f"  - recorded humidity: {humidity}")
+  if is_usb_power:
+    adjusted_temperature = temperature - config.usb_power_temperature_offset
+    logging.info(f"  - USB temperature offset: {config.usb_power_temperature_offset}")
+  else:
+    adjusted_temperature = temperature - config.battery_power_temperature_offset
+    logging.info(f"  - Battery temperature offset: {config.battery_power_temperature_offset}")
+  absolute_humidity = helpers.relative_to_absolute_humidity(humidity, temperature)
+  humidity = helpers.absolute_to_relative_humidity(absolute_humidity, adjusted_temperature)
+  temperature = adjusted_temperature
+  logging.info(f"  - adjusted temperature: {temperature}")
+  logging.info(f"  - adjusted humidity: {humidity}")
+
   from ucollections import OrderedDict
   return OrderedDict({
-    "temperature": round(bme280_data[0], 2),
-    "humidity": round(bme280_data[2], 2),
+    "temperature": round(temperature, 2),
+    "humidity": round(humidity, 2),
     "pressure": round(bme280_data[1] / 100.0, 2),
     "luminance": round(ltr_data[BreakoutLTR559.LUX], 2),
     "wind_speed": wind_speed(),

enviro/config_defaults.py

@@ -2,6 +2,7 @@
 from phew import logging
 
 DEFAULT_USB_POWER_TEMPERATURE_OFFSET = 4.5
+DEFAULT_BATTERY_POWER_TEMPERATURE_OFFSET = 0.0
 
 
 def add_missing_config_settings():
@@ -17,6 +18,12 @@ def add_missing_config_settings():
   except AttributeError:
     warn_missing_config_setting("usb_power_temperature_offset")
     config.usb_power_temperature_offset = DEFAULT_USB_POWER_TEMPERATURE_OFFSET
+
+  try:
+    config.battery_power_temperature_offset
+  except AttributeError:
+    warn_missing_config_setting("battery_power_temperature_offset")
+    config.battery_power_temperature_offset = DEFAULT_BATTERY_POWER_TEMPERATURE_OFFSET
 
 
 def warn_missing_config_setting(setting):

enviro/config_template.py

@@ -53,4 +53,10 @@
 moisture_target_c = 50
 
 # compensate for usb power
+# degrees to remove from measured temperature when running on USB
 usb_power_temperature_offset = 4.5
+
+# compensate for battery power (only on weather boards)
+# degrees to remove from measured temperature when running on battery
+# this will vary based on poll and wifi upload frequency with accumulated heat as these values increase
+battery_power_temperature_offset = 0.0