feat(examples):Add absolute humidity mode

diff --git a/examples/all-in-one-enviro-mini-bk.py b/examples/all-in-one-enviro-mini-bk.py
index bff5497ed41360cecb9b9734ef7f9a7aa7ef6f9e..8913cef932c24dda27d91e6cfe62527dcfcc0a9e 100755 (executable)
--- a/examples/all-in-one-enviro-mini-bk.py
+++ b/examples/all-in-one-enviro-mini-bk.py
@@ -142,6 +142,75 @@ def get_cpu_temperature():
     output, _error = process.communicate()
     return float(output[output.index('=') + 1:output.rindex("'")])
 
+def rel_to_abs(T,P,RH):
+    """Returns absolute humidity given relative humidity.
+
+    Inputs:
+    --------
+    T : float
+        Absolute temperature in units Kelvin (K).
+    P : float
+        Total pressure in units Pascals (Pa).
+    RH : float
+        Relative humidity in units percent (%).
+
+    Output:
+    --------
+    absolute_humidity : float
+        Absolute humidity in units [kg water vapor / kg dry air].
+
+    References:
+    --------
+    1. Sonntag, D. "Advancements in the field of hygrometry". 1994. https://doi.org/10.1127/metz/3/1994/51
+    2. Green, D. "Perry's Chemical Engineers' Handbook" (8th Edition). Page "12-4". McGraw-Hill Professional Publishing. 2007.
+
+    Version: 0.0.1
+    Author: Steven Baltakatei Sandoval
+    License: GPLv3+
+    """
+
+    import math;
+
+    # Check input types
+    T = float(T);
+    P = float(P);
+    RH = float(RH);
+
+    #debug
+    # print('DEBUG:Input Temperature   (K)  :' + str(T));
+    # print('DEBUG:Input Pressure      (Pa) :' + str(P));
+    # print('DEBUG:Input Rel. Humidity (%)  :' + str(RH));
+
+    # Set constants and initial conversions
+    epsilon = 0.62198 # (molar mass of water vapor) / (molar mass of dry air)
+    t = T - 273.15; # Celsius from Kelvin
+    P_hpa = P / 100; # hectoPascals (hPa) from Pascals (Pa)
+
+    # Calculate e_w(T), saturation vapor pressure of water in a pure phase, in Pascals
+    ln_e_w = -6096*T**-1 + 21.2409642 - 2.711193*10**-2*T + 1.673952*10**-5*T**2 + 2.433502*math.log(T); # Sonntag-1994 eq 7; e_w in Pascals
+    e_w = math.exp(ln_e_w);
+    e_w_hpa = e_w / 100; # also save e_w in hectoPascals (hPa)
+    # print('DEBUG:ln_e_w:' + str(ln_e_w)); # debug
+    # print('DEBUG:e_w:' + str(e_w)); # debug
+
+    # Calculate f_w(P,T), enhancement factor for water
+    f_w = 1 + (10**-4*e_w_hpa)/(273 + t)*(((38 + 173*math.exp(-t/43))*(1 - (e_w_hpa / P_hpa))) + ((6.39 + 4.28*math.exp(-t / 107))*((P_hpa / e_w_hpa) - 1))); # Sonntag-1994 eq 22.
+    # print('DEBUG:f_w:' + str(f_w)); # debug
+
+    # Calculate e_prime_w(P,T), saturation vapor pressure of water in air-water mixture, in Pascals
+    e_prime_w = f_w * e_w; # Sonntag-1994 eq 18
+    # print('DEBUG:e_prime_w:' + str(e_prime_w)); # debug
+
+    # Calculate e_prime, vapor pressure of water in air, in Pascals
+    e_prime = (RH / 100) * e_prime_w;
+    # print('DEBUG:e_prime:' + str(e_prime)); # debug
+
+    # Calculate r, the absolute humidity, in [kg water vapor / kg dry air]
+    r = (epsilon * e_prime) / (P - e_prime);
+    # print('DEBUG:r:' + str(r)); # debug
+
+    return float(r);
+
 
 # Tuning factor for compensation. Decrease this number to adjust the
 # temperature down, and increase to adjust up
@@ -158,6 +227,7 @@ light = 1
 variables = ["temperature",
              "pressure",
              "humidity",
+             "humidity_abs",
              "light"]
 values = {} # Initialize values dictionary
 for v in variables:
@@ -186,13 +256,15 @@ def pollSensors():
     #         now_temp_tuple (°C)
     #         now_pressure_tuple (hPa)
     #         now_humidity_tuple (%)
+    #         now_humidity_abs_tuple (g water vapor / kg dry air)
     #         now_illuminance_tuple (lux)
-    # Depends: time, bme280, ltr559, get_cpu_temperature()
+    # Depends: time, bme280, ltr559, get_cpu_temperature(), rel_to_abs()
 
     # Tell function to modify these global variables
     global now_temp_tuple
     global now_pressure_tuple
     global now_humidity_tuple
+    global now_humidity_abs_tuple
     global now_illuminance_tuple
     # Initialize
     cpu_temps = []
@@ -209,9 +281,14 @@ def pollSensors():
     now_time_ns = time.time_ns() # Get time reading (unix epoch, nanoseconds)
     now_pressure = bme280.get_pressure() # get hPa from BME280 sensor
     now_pressure_tuple = (time.time_ns(), 'hPa', now_pressure)
-    # Get humidity reading
-    now_humidity = bme280.get_humidity() # get % humidity from BME280 sensor
+    # Get relative humidity reading
+    now_humidity = bme280.get_humidity() # get % relative humidity from BME280 sensor
     now_humidity_tuple = (time.time_ns(), '%', now_humidity)
+    # Calculate absolute humidity reading
+    raw_temp_k = 273.15 + raw_temp; # convert sensor temp from degC to K
+    now_pressure_pa = now_pressure * 100; # convert sensor pressure from hPa to Pa
+    now_humidity_abs = rel_to_abs(raw_temp_k,now_pressure_pa,now_humidity); # calc abs humidity
+    now_humidity_abs_tuple = (time.time_ns(), 'g/kg', now_humidity_abs);
     # Get light reading
     proximity = ltr559.get_proximity() # get proximity reading
     if proximity < 10:
@@ -309,6 +386,7 @@ def updateBuffer():
     global now_temp_tuple
     global now_pressure_tuple
     global now_humidity_tuple
+    global now_humidity_abs_tuple
     global now_illuminance_tuple
     global varLenBuffer
     global fixLenBuffer
@@ -322,6 +400,7 @@ def updateBuffer():
     #print('DEBUG:now_temp_tuple:' + str(now_temp_tuple))
     #print('DEBUG:now_pressure_tuple:' + str(now_pressure_tuple))
     #print('DEBUG:now_humidity_tuple:' + str(now_humidity_tuple))
+    #print('DEBUG:now_humidity_abs_tuple:' + str(now_humidity_abs_tuple))
     #print('DEBUG:now_illuminance_tuple:' + str(now_illuminance_tuple))    
 
     # Append new sensor tuples to varying-length buffer
@@ -329,10 +408,12 @@ def updateBuffer():
     varLenBuffer[variables[0]].append(now_temp_tuple)
     ## Pressure
     varLenBuffer[variables[1]].append(now_pressure_tuple)
-    ## Humidity
+    ## Relative Humidity
     varLenBuffer[variables[2]].append(now_humidity_tuple)
+    ## Absolute Humidity
+    varLenBuffer[variables[3]].append(now_humidity_abs_tuple)
     ## Illuminance
-    varLenBuffer[variables[3]].append(now_illuminance_tuple)
+    varLenBuffer[variables[4]].append(now_illuminance_tuple)
     #print('DEBUG:varLenBuffer:' + str(varLenBuffer))
 
     # Trim outdated sensor tuples from varying-length buffer
@@ -445,8 +526,19 @@ try:
             data = bme280.get_humidity()
             #display_text(variables[mode], data, unit)
             display_text2(variables[mode],data,unit,fixLenBuffer)
-            
+
         if mode == 3:
+            # variable = "humidity_abs"
+            unit = "g/kg"
+            raw_temp = bme280.get_temperature() # get °C from BME280 sensor
+            raw_temp_k = 273.15 + raw_temp; # convert sensor temp from degC to K
+            now_pressure = bme280.get_pressure() # get hPa from BME280 sensor
+            now_pressure_pa = now_pressure * 100; # convert sensor pressure from hPa to Pa
+            now_humidity = bme280.get_humidity() # get % relative humidity from BME280 sensor
+            data = rel_to_abs(raw_temp_k,now_pressure_pa,now_humidity); # calc abs humidity
+            display_text2(variables[mode],data,unit,fixLenBuffer)
+            
+        if mode == 4:
             # variable = "light"
             unit = "Lux"
             if proximity < 10: