Adjust temperature under usb power

enviro/__init__.py

@@ -469,6 +469,11 @@ def sleep(time_override=None):
   rtc.set_alarm(0, minute, hour)
   rtc.enable_alarm_interrupt(True)
 
+  # assume we're running on battery power
+  logging.debug("assume battery power in config")
+  config.usb_power = False
+  helpers.write_config(config)
+
   # disable the vsys hold, causing us to turn off
   logging.info("  - shutting down")
   hold_vsys_en_pin.init(Pin.IN)
@@ -477,6 +482,12 @@ def sleep(time_override=None):
   # case we can't (and don't need to) sleep.
   stop_activity_led()
 
+  # indicate that we're running on usb power - which requires temperature
+  # and humidity adjustments.
+  logging.debug("switching config to usb power")
+  config.usb_power = True
+  helpers.write_config(config)
+
   # if running via mpremote/pyboard.py with a remote mount then we can't
   # reset the board so just exist
   if phew.remote_mount:

enviro/boards/indoor.py

@@ -1,7 +1,9 @@
+import enviro.helpers as helpers
 import math
 from breakout_bme68x import BreakoutBME68X
 from breakout_bh1745 import BreakoutBH1745
 
+from enviro import config
 from enviro import i2c
 
 bme688 = BreakoutBME68X(i2c, address=0x77)
@@ -44,8 +46,17 @@ def get_sensor_readings(seconds_since_last):
   data = bme688.read()
 
   temperature = round(data[0], 2)
-  pressure = round(data[1] / 100.0, 2)
   humidity = round(data[2], 2)
+
+  # Compensate for additional heating when on usb power - this also changes the
+  # relative humidity value.
+  if config.usb_power:
+    adjusted_temperature = temperature - config.usb_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
+
+  pressure = round(data[1] / 100.0, 2)
   gas_resistance = round(data[3])
   # an approximate air quality calculation that accounts for the effect of
   # humidity on the gas sensor
@@ -64,4 +75,4 @@ def get_sensor_readings(seconds_since_last):
     "aqi": aqi,
     "luminance": lux_from_rgbc(r, g, b, c),
     "color_temperature": colour_temperature_from_rgbc(r, g, b, c)
-  })
+  })

enviro/config_template.py

@@ -47,4 +47,8 @@
 auto_water = False
 moisture_target_a = 50
 moisture_target_b = 50
-moisture_target_c = 50
+moisture_target_c = 50
+
+# compensate for usb power
+usb_power = False
+usb_power_temperature_offset = 4

enviro/constants.py

@@ -40,3 +40,8 @@
 UPLOAD_SUCCESS = 0
 UPLOAD_FAILED = 1
 UPLOAD_RATE_LIMITED = 2
+
+# humidity
+WATER_VAPOR_SPECIFIC_GAS_CONSTANT = 461.5
+CRITICAL_WATER_TEMPERATURE = 647.096
+CRITICAL_WATER_PRESSURE = 22064000

enviro/helpers.py

@@ -1,5 +1,5 @@
 from enviro.constants import *
-import machine, os, time
+import machine, math, os, time
 
 # miscellany
 # ===========================================================================
@@ -57,3 +57,61 @@ def copy_file(source, target):
         if not chunk:
           break
         outfile.write(chunk)
+
+def write_config(config):
+  lines = []
+  with open("config.py", "r") as infile:
+    lines = infile.read().split("\n")
+
+  for i in range(0, len(lines)):
+    line = lines[i]
+    parts = line.split("=", 1)
+    if len(parts) == 2:
+      key = parts[0].strip()
+      if hasattr(config, key):
+        value = getattr(config, key)
+        lines[i] = f"{key} = {repr(value)}"
+
+  with open("config.py", "w") as outfile:
+    outfile.write("\n".join(lines))
+
+# temperature and humidity helpers
+# ===========================================================================
+
+# https://www.calctool.org/atmospheric-thermodynamics/absolute-humidity#what-is-and-how-to-calculate-absolute-humidity
+def relative_to_absolute_humidity(relative_humidity, temperature_in_c):
+  temperature_in_k = celcius_to_kelvin(temperature_in_c)
+  actual_vapor_pressure = get_actual_vapor_pressure(relative_humidity, temperature_in_k)
+
+  return actual_vapor_pressure / (WATER_VAPOR_SPECIFIC_GAS_CONSTANT * temperature_in_k)
+
+def absolute_to_relative_humidity(absolute_humidity, temperature_in_c):
+  temperature_in_k = celcius_to_kelvin(temperature_in_c)
+  saturation_vapor_pressure = get_saturation_vapor_pressure(temperature_in_k)
+
+  return (WATER_VAPOR_SPECIFIC_GAS_CONSTANT * temperature_in_k * absolute_humidity) / saturation_vapor_pressure * 100
+
+def celcius_to_kelvin(temperature_in_c):
+  return temperature_in_c + 273.15
+
+# https://www.calctool.org/atmospheric-thermodynamics/absolute-humidity#actual-vapor-pressure
+# http://cires1.colorado.edu/~voemel/vp.html
+def get_actual_vapor_pressure(relative_humidity, temperature_in_k):
+  return get_saturation_vapor_pressure(temperature_in_k) * (relative_humidity / 100)
+
+def get_saturation_vapor_pressure(temperature_in_k):
+  v = 1 - (temperature_in_k / CRITICAL_WATER_TEMPERATURE)
+
+  # empirical constants
+  a1 = -7.85951783
+  a2 = 1.84408259
+  a3 = -11.7866497
+  a4 = 22.6807411
+  a5 = -15.9618719
+  a6 = 1.80122502
+
+  return CRITICAL_WATER_PRESSURE * math.exp(
+      CRITICAL_WATER_TEMPERATURE /
+      temperature_in_k *
+      (a1*v + a2*v**1.5 + a3*v**3 + a4*v**3.5 + a5*v**4 + a6*v**7.5)
+  )

enviro/provisioning.py

@@ -12,24 +12,6 @@
 if not helpers.file_exists("config.py"):
   helpers.copy_file("enviro/config_template.py", "config.py")
 
-# write the current values in config to the config.py file
-def write_config():
-  lines = []
-  with open("config.py", "r") as infile:
-    lines = infile.read().split("\n")
-
-  for i in range(0, len(lines)):
-    line = lines[i]
-    parts = line.split("=", 1)
-    if len(parts) == 2:
-      key = parts[0].strip()
-      if hasattr(config, key):
-        value = getattr(config, key)
-        lines[i] = f"{key} = {repr(value)}"
-
-  with open("config.py", "w") as outfile:
-    outfile.write("\n".join(lines))
-
 import config
 
 
@@ -71,7 +53,7 @@ def provision_welcome(request):
 def provision_step_1_nickname(request):
   if request.method == "POST":
     config.nickname = request.form["nickname"]
-    write_config()
+    helpers.write_config(config)
     return redirect(f"http://{DOMAIN}/provision-step-2-wifi")
   else:
     return render_template("enviro/html/provision-step-1-nickname.html", board=model)
@@ -82,7 +64,7 @@ def provision_step_2_wifi(request):
   if request.method == "POST":
     config.wifi_ssid = request.form["wifi_ssid"]
     config.wifi_password = request.form["wifi_password"]
-    write_config()
+    helpers.write_config(config)
     return redirect(f"http://{DOMAIN}/provision-step-3-logging")
   else:
     return render_template("enviro/html/provision-step-2-wifi.html", board=model)
@@ -93,7 +75,7 @@ def provision_step_3_logging(request):
   if request.method == "POST":
     config.reading_frequency = int(request.form["reading_frequency"])
     config.upload_frequency = int(request.form["upload_frequency"]) if request.form["upload_frequency"] else None
-    write_config()
+    helpers.write_config(config)
     return redirect(f"http://{DOMAIN}/provision-step-4-destination")
   else:
     return render_template("enviro/html/provision-step-3-logging.html", board=model)
@@ -124,7 +106,7 @@ def provision_step_4_destination(request):
     config.influxdb_token = request.form["influxdb_token"]
     config.influxdb_bucket = request.form["influxdb_bucket"]
 
-    write_config()
+    helpers.write_config(config)
 
     if model == "grow":
       return redirect(f"http://{DOMAIN}/provision-step-grow-sensors")
@@ -153,7 +135,7 @@ def provision_step_grow_sensors(request):
     except ValueError:
       pass
 
-    write_config()
+    helpers.write_config(config)
 
     return redirect(f"http://{DOMAIN}/provision-step-5-done")
   else:
@@ -163,7 +145,7 @@ def provision_step_grow_sensors(request):
 @server.route("/provision-step-5-done", methods=["GET", "POST"])
 def provision_step_5_done(request):
   config.provisioned = True
-  write_config()
+  helpers.write_config(config)
 
   # a post request to the done handler means we're finished and
   # should reset the board
@@ -207,4 +189,4 @@ def catchall(request):
 logging.info("  - client connected!", ap.status("stations")[0])
 
 logging.info("> running provisioning application...")
-server.run(host="0.0.0.0", port=80)
+server.run(host="0.0.0.0", port=80)

main.py

@@ -73,9 +73,9 @@
   # here you can customise the sensor readings by adding extra information
   # or removing readings that you don't want, for example:
   # 
-  #   del readings["temperature"]        # remove the temperature reading
+  #   del reading["temperature"]        # remove the temperature reading
   #
-  #   readings["custom"] = my_reading()  # add my custom reading value
+  #   reading["custom"] = my_reading()  # add my custom reading value
 
   # is an upload destination set?
   if enviro.config.destination: