Calculation for g/m^3

RaspberryPi/.gitignore

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+*.c~
+*.h~

RaspberryPi/calculate.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <math.h> /* link against math lib */
+#include "calculate.h"
+
+
+/*
+Bezeichnungen:
+r = relative Luftfeuchte
+T = Temperatur in °C
+TK = Temperatur in Kelvin (TK = T + 273.15)
+TD = Taupunkttemperatur in °C
+DD = Dampfdruck in hPa
+SDD = Sättigungsdampfdruck in hPa
+
+Parameter:
+a = 7.5, b = 237.3 für T >= 0
+a = 7.6, b = 240.7 für T < 0 über Wasser (Taupunkt)
+a = 9.5, b = 265.5 für T < 0 über Eis (Frostpunkt)
+
+R* = 8314.3 J/(kmol*K) (universelle Gaskonstante)
+mw = 18.016 kg/kmol (Molekulargewicht des Wasserdampfes)
+AF = absolute Feuchte in g Wasserdampf pro m3 Luft
+
+Formeln:
+
+    SDD(T) = 6.1078 * 10^((a*T)/(b+T))
+    DD(r,T) = r/100 * SDD(T)
+    r(T,TD) = 100 * SDD(TD) / SDD(T)
+    TD(r,T) = b*v/(a-v) mit v(r,T) = log10(DD(r,T)/6.1078)
+    AF(r,TK) = 10^5 * mw/R* * DD(r,T)/TK; AF(TD,TK) = 10^5 * mw/R* * SDD(TD)/TK
+*/
+
+float sdd(float temperature) {
+  //select constant based on input temperature
+  float a = 7.5, b = 237.3;
+  if (sensor->temperature >= 0) {
+    a = 7.6;
+    b = 240.7;
+  } 
+  return 6.1078 * pow(10, (a*temperature) / (b*temperature));
+}
+
+float dd(float relativeHumidity, float temperature) {
+  return relativeHumidity / 100 * sdd(temperature);
+}
+
+float r(float temperature, float dewTemperature) {
+  /* This is optional. Necessary with dew point measurements. */
+  return 100 * sdd(dewTemperature) / sdd(temperature);
+}
+
+//TD(r,T) = b*v/(a-v) mit v(r,T) = log10(DD(r,T)/6.1078)
+
+float v(float relativeHumidity, float temperature) {
+  log10(dd(relativeHumidity, temperature)/6.1078);
+}
+
+float td(float relativeHumidity, float temperature) {
+  //select constant based on input temperature
+  float a = 7.5, b = 237.3;
+  if (sensor->temperature >= 0) {
+    a = 7.6;
+    b = 240.7;
+  } 
+  return b * v(relativeHumidity, temperature) / (a - v(relativeHumidity, temperature));
+}
+
+float absoluteHumidity(sensor *sensor) {
+  //select constant based on input temperature
+  float a = 7.5, b = 237.3;
+  if (sensor->temperature >= 0) {
+    a = 7.6;
+    b = 240.7;
+  }
+  
+  
+  float sdd_T = sdd(sensor->temperature);
+  float dd = dd(sensor->humidity, sensor->temperature);
+  float relativeHumidity = r( 
+
+}
+  

RaspberryPi/calculate.h

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+/* Include guard */
+#include "dht22.h"
+
+double absoluteHumidity(sensor *sensor);