The Nicla Sense ME is a wonderful board that has a multitude of sensors. For this project, I am using all the sensors available on the Nicla in different ways, and one of my objective for the project, was to enchance the outputs available by using Physics formulas and mathematics to derivate other meaninful data.
As I have talked in one of my latest posts (available here: https://ciprianaa30.wixsite.com/aurismartwatch/post/compass-nicla-sense-me) I added a compass function based on the Nicla Magnetometer and Accelerometer.
Secondly, I have talked in the past how I used the hypsometric formula to calculate the altitude from the level of the sea, by using the pressure and temperature.
temp_value - 0.55 * (1 -0.01 * hum_value) * (temp_value - 14.5); By using the research paper "Bolton 1980 - The Computation of Equivalent Potential Temperature"(https://journals.ametsoc.org/view/journals/mwre/108/7/1520-0493_1980_108_1046_tcoept_2_0_co_2.xml), I can calculate the Relative Humidity from the humidity value, pressure and temperature.
((hum_value * pressure_value)/(0.378 * hum_value + 0.622))/(6.112 * exp((17.67 * temp_value)/(temp_value+243.5)));Now, thanks to the Relative Humidity, the Air Dew Point, the temperature to which air must be cooled to become saturated with water vapor, can be calculated in 2 ways, the second being more complex, but ultimately more accurate:
method1 = temp_value - ((100-relative_humidity)/5);
method2 = (243.12 * (log(relative_humidity/100) + ((17.62* temp_value)/(243.12+temp_value)))) / (17.62 - (log(relative_humidity/100) + ((17.62* temp_value)/(243.12+temp_value))));With only the temperature, I can calculate the Saturation Vapor Pressure, necessary to calculate the Air Density.
6.1078 * pow(10, ((7.5*temp_value)/(temp_value + 237.3))); With the Saturation Vapor Pressure calculated, I can derive the pressure of the water vapor and the pressure of the dry air. Moist air, which is the common type of air in the real world (not a lab) creates a pressure force that is equal to the sum of the 2 separate pressures. The calculation happens thanks to the Relative Humidity and the total Barometric Pressure.
float water_vapor_pressure = (saturation_vapor_pressure * relative_humidity)/100;
float dry_air_pressure = pressure_value - water_vapor_pressure;Now that we have all these values, we can calculate the Air Density in kg/m^3(kilograms per cubic meter). An in depth explanation of the formulas with an online calculator is available here: https://www.omnicalculator.com/physics/air-density#how-to-calculate-the-air-density
float air_density = ((dry_air_pressure/(dry_air_constant * (temp_value+273.15))) + (water_vapor_pressure / ( water_vapor_constant * (temp_value+273.15))))*100;Thanks to the Saturation Vapor Pressure and Relative Humidity, I can calculate the Absolute Humidity. The mass of water vapor in a unit volume of air. It is a measure of the actual water vapor content of the air. Expressed in kilograms per cubic meter of moist air. More details here: https://planetcalc.com/2167/. I have used the double precision because of the measurement type, as specified this is in kg/m^3, which creates an output similar to 0.000189, in this case decimals long after the point can highly affect the output.
double absolute_humidity = (((saturation_vapor_pressure * relative_humidity)/10) / (water_vapor_constant * temp_value)) ;With the Temperature and Relative Humidity, I can calculate the Heat Index which represents the felt air temperature. This does not take into consideration activities such as running or hiking or direct sunlight. It is an index to be used for regular outdoor walking activities. More information here: //https://ncalculators.com/meteorology/heat-index-calculator.htm
float heat_index_part1 = -42.379+(2.04901523*temp_value)+(10.14333127*relative_humidity)-(0.22475541*temp_value*relative_humidity)-(6.83783*pow(10,-3)*pow(temp_value,2))-(5.481717*pow(10,-2)*pow(relative_humidity,2)) ;
float heat_index_part2 = +(1.22874*pow(10, -3)*pow(temp_value,2)*relative_humidity)+(8.5282*pow(10, -4)*temp_value*pow(relative_humidity,2))-(1.99*pow(10, -6) *pow(temp_value, 2)*pow(relative_humidity, 2));
int heat_index = heat_index_part1 + heat_index_part2; And lastly the 2 extra values that can be calculated are Cloud Base Altitude and Cloud Base Temperature. This can inform us at what altitude from the level of the sea or our current elevation, do the clouds form. Useful information for navigation and piloting. Moreover, the temperature of the clouds can also be calculated. The lower the temperature, the higher the chance for rain or fog.
float cloud_base_altitude = 125 * (temp_value - air_dew_point_accurate) + altitude;
int cloud_base_temperature = ((1.8*temp_value + 32) - 5.4*((cloud_base_altitude - altitude)*3.28084) - 32) * 5/9;
Finally, the output looks as following:
And the whole code looks like this:
//------------------------------------------------------------------------------------------------------------------------------------------------------------------------
//--------------------------------------------------------------------------LIBRARIES-------------------------------------------------------------------------------
//------------------------------------------------------------------------------------------------------------------------------------------------------------------------
#include "Arduino_BHY2.h"
#include "Nicla_System.h"
//------------------------------------------------------------------------------------------------------------------------------------------------------------------------
//-------------------------------------------------------------------------DECLARATIONS------------------------------------------------------------------------
//------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Sensor humidity(SENSOR_ID_HUM);
Sensor temperature(SENSOR_ID_TEMP);
Sensor pressure(SENSOR_ID_BARO);
Sensor gas(SENSOR_ID_GAS);
SensorBSEC bsec(SENSOR_ID_BSEC);
SensorOrientation orientation(SENSOR_ID_ORI);
Sensor tilt(SENSOR_ID_WRIST_TILT_GESTURE);
String voc_air_quality = "";
String iaq_air_quality = "";
String co2_air_quality = "";
String pressure_effect ="";
String discomfort_condition = "";
String heat_index_condition ="";
float sea_level_pressure = 1013.25;
float dry_air_constant = 287.058; //specific gas constant for dry air equal in J/(kg·K)
float water_vapor_constant = 461.495; //specific gas constant for water vapor in J/(kg·K)
String compass_array[13];
int StringCount = 0;
String compass_heading = "";
//------------------------------------------------------------------------------------------------------------------------------------------------------------------------
//-------------------------------------------------------------------------SYSTEM SETUP------------------------------------------------------------------------
//------------------------------------------------------------------------------------------------------------------------------------------------------------------------
void setup(){
nicla::begin();
Serial.begin(115200);
BHY2.begin();
temperature.begin();
humidity.begin();
pressure.begin();
gas.begin();
bsec.begin();
orientation.begin();
tilt.begin();
}
//------------------------------------------------------------------------------------------------------------------------------------------------------------------------
//---------------------------------------------------------------------------MAIN CODE-----------------------------------------------------------------------------
//------------------------------------------------------------------------------------------------------------------------------------------------------------------------
void loop(){
static auto lastCheck= millis();
BHY2.update();
// Check sensor values every second
if (millis() - lastCheck >= 2000) {
lastCheck = millis();
//the word "Temperature" is already taken by the Nicla board, so I use "temp_value"
float temp_value = temperature.value();
int hum_value = humidity.value();
int gas_resistance = gas.value();
float pressure_value = pressure.value();
int iaq = ((bsec.toString()).substring(25,28)).toInt();
float voc_eq = ((bsec.toString()).substring(53,57)).toFloat();
int co2_eq = ((bsec.toString()).substring(68,72)).toInt();
int accuracy = ((bsec.toString()).substring(84,85)).toInt();
float comp_temp = ((bsec.toString()).substring(95,101)).toFloat();
int comp_hum = ((bsec.toString()).substring(112,117)).toInt();
int comp_gas_res = ((bsec.toString()).substring(128,130)).toInt();
string_separator(orientation.toString(), compass_array, 0);
float heading = (compass_array[4]).toFloat() + 28;
float roll = (compass_array[12]).toFloat();
float temp_fusion = (temp_value+comp_temp)/2;
float humidity_fusion = (hum_value+comp_hum)/2;
int altitude = ((pow((sea_level_pressure/pressure_value), (1/5.257)) -1) * (temp_value + 273.15))/0.0065; //altitude hypsometric formula
int discomfort_index = temp_value - 0.55 * (1 -0.01 * hum_value) * (temp_value - 14.5); //discomfort index formula
//the ratio of the actual amount of water vapor in the air to the amount it could hold when saturated
float relative_humidity = ((hum_value * pressure_value)/(0.378 * hum_value + 0.622))/(6.112 * exp((17.67 * temp_value)/(temp_value+243.5))); // relative humidity from Bolton 1980 The computation of Equivalent Potential Temperature
float air_dew_point = temp_value - ((100-relative_humidity)/5); //The dew point is the temperature to which air must be cooled to become saturated with water vapor
float air_dew_point_accurate = (243.12 * (log(relative_humidity/100) + ((17.62* temp_value)/(243.12+temp_value)))) / (17.62 - (log(relative_humidity/100) + ((17.62* temp_value)/(243.12+temp_value))));
float saturation_vapor_pressure = 6.1078 * pow(10, ((7.5*temp_value)/(temp_value + 237.3))); //from https://www.omnicalculator.com/physics/air-density#how-to-calculate-the-air-density
float water_vapor_pressure = (saturation_vapor_pressure * relative_humidity)/100; //multiplication of saturation vapor pressure with the relative humidity, divided by 100%
float dry_air_pressure = pressure_value - water_vapor_pressure;
float air_density = ((dry_air_pressure/(dry_air_constant * (temp_value+273.15))) + (water_vapor_pressure / ( water_vapor_constant * (temp_value+273.15))))*100; //air density formula, can be used for air buoyancy
//the mass of water vapor in a unit volume of air. It is a measure of the actual water vapor content of the air.
double absolute_humidity = (((saturation_vapor_pressure * relative_humidity)/10) / (water_vapor_constant * temp_value)) ; //expressed in kilograms per cubic meter of moist air - https://planetcalc.com/2167/
//https://ncalculators.com/meteorology/heat-index-calculator.htm
float heat_index_part1 = -42.379+(2.04901523*temp_value)+(10.14333127*relative_humidity)-(0.22475541*temp_value*relative_humidity)-(6.83783*pow(10,-3)*pow(temp_value,2))-(5.481717*pow(10,-2)*pow(relative_humidity,2)) ;
float heat_index_part2 = +(1.22874*pow(10, -3)*pow(temp_value,2)*relative_humidity)+(8.5282*pow(10, -4)*temp_value*pow(relative_humidity,2))-(1.99*pow(10, -6) *pow(temp_value, 2)*pow(relative_humidity, 2));
int heat_index = heat_index_part1 + heat_index_part2; //felt air temperature, does not take into consideration direct sunlight effect
//https://www.omnicalculator.com/physics/cloud-base#how-to-use-the-cloud-altitude-calculator
float cloud_base_altitude_method1 = 125 * (temp_value - air_dew_point_accurate) + altitude;
float cloud_base_altitude_method2 = ((1.8*( temp_value - air_dew_point_accurate)+64) / 4.4) * 1000 + altitude*3.28084;
int cloud_base_temperature = ((1.8*temp_value + 32) - 5.4*((cloud_base_altitude_method1 - altitude)*3.28084) - 32) * 5/9;
if (voc_eq <= 5.0) voc_air_quality = "Clean Air! No Volatile Detected!";
else if (5.0 < voc_eq <= 10.0) voc_air_quality = "Ethane Alkane Detected!";
else if (10.0 < voc_eq <= 15.0) voc_air_quality = "Isoprene/Methyl/Butadiene/Ethanol Detected!";
else if (15.0 < voc_eq <= 50.0) voc_air_quality = "Carbon Monoxide Detected!";
else if (voc_eq > 50.0) voc_air_quality = "Acetone Detected!";
if (iaq <= 50) iaq_air_quality = "Pure air. No measures needed!";
else if (50 < iaq <= 100) iaq_air_quality = "Good Air! No irritation or impact on well-being. No health measures needed! ";
else if (100 < iaq <= 150) iaq_air_quality = "Lightly polluted air! Reduction of well-being possible! Fresh air or ventilation suggested!";
else if (150 < iaq <= 200) iaq_air_quality = "Moderately polluted. Reduction of well-being possible! Increase ventilation with clean air!";
else if (200 < iaq <= 250) iaq_air_quality = "Heavily polluted. Continous exposition might lead to migraines! Immediately increase ventilation or leave the environment!";
else if (250 < iaq <= 350) iaq_air_quality = "Severely polluted. Severe health issues possible! Contamination should be identified! Maximise ventilation or leave environment";
else if (iaq > 350) iaq_air_quality = "Extremely polluted. Neurotoxic effects possible! Contamination must be identified! Avoid the environment!";
if (co2_eq <= 400) co2_air_quality = "Normal CO2 concentration in outdoor ambient air!";
else if (400 < co2_eq <= 600) co2_air_quality = "Excellent air! CO2 concentrations typical of occupied indoor spaces with good air exchange!";
else if (600 < co2_eq <= 900) co2_air_quality = "Good air! CO2 concentrations typical of occupied indoor spaces with decent air exchange!";
else if (900 < co2_eq <= 1100) co2_air_quality = "Fair air! CO2 concentrations typical of occupied indoor spaces with no air exchange!";
else if (1100 < co2_eq <= 1600) co2_air_quality = "Mediocre air! High CO2 concentrations! Increase ventilation or leave environment!";
else if (1600 < co2_eq <= 2000) co2_air_quality = "Bad air! High CO2 concentrations! Ventilation necessary! Leave environment!";
else if (2000 < co2_eq <= 5000) co2_air_quality = "Headaches, sleepiness, increased heart rate and slight nausea can be caused. Leave environment immediately!";
else if (5000 < co2_eq < 40000) co2_air_quality = "Environment exposure may lead to oxygen deprivation resulting in adverse health effects. Leave environment immediately!";
else if (co2_eq > 40000) co2_air_quality = "Environment exposure may lead to oxygen deprivation resulting in permanent brain damage and coma! Leave environment urgently!";
if (discomfort_index <= 21) discomfort_condition = "No discomfort!";
else if (21 < discomfort_index <= 25) discomfort_condition = "Under 50% of the population feels discomfort!";
else if (24 < discomfort_index <= 27) discomfort_condition = "Over 50% of the population feels discomfort!";
else if (27 < discomfort_index <= 29) discomfort_condition = "Most of the population suffers discomfort!";
else if (29 < discomfort_index <= 32) discomfort_condition = "Discomfort Index High! The environment will cause severe stress!";
else if (discomfort_index > 32) discomfort_condition = "State of medical emergency! Please leave environment!";
if (pressure_value > 1022.678) pressure_effect = "Caution! High pressure which pushes against the body and limits how much the tissue can expand. Potential of joint paint!";
else if (pressure_value < 1007) pressure_effect = "Caution! Low pressure allowing the body's tissues to expand, affecting the nerves, which can cause migraines!";
else if (1007 <= pressure_value <= 1022.678) pressure_effect = "Expected pressure range!";
if (27 <= heat_index <= 32) heat_index_condition = "Caution Advised. High heat!";
else if (33 <= heat_index <= 39) heat_index_condition = "Increased Caution Advised. High heat!";
else if (40 <= heat_index <= 51) heat_index_condition = "Danger! Only stay outdoor if necessary!";
else if (heat_index > 52) heat_index_condition = "Extreme Danger! Do not stay oudoor, migraine and negative skin effects possible!";
if (0 <= heading <= 11.25) compass_heading = "You are heading NORTH!";
else if (348.75 < heading <= 360) compass_heading = "You are heading NORTH!";
else if (78.75 < heading <= 101.25) compass_heading = "You are heading EAST!";
else if (168.75 < heading <= 191.25) compass_heading = "You are heading SOUTH!";
else if (258.75 < heading <= 281.25) compass_heading = "You are heading WEST!";
else if (33.75 < heading <= 56.25) compass_heading = "You are heading NORTH-EAST!";
else if (123.75 < heading <= 146.25) compass_heading = "You are heading SOUTH-EAST!";
else if (213.75 < heading <= 236.25) compass_heading = "You are heading SOUTH-WEST!";
else if (303.75 < heading <= 326.25) compass_heading = "You are heading NORTH-WEST!";
else if (11.25 < heading <= 33.75) compass_heading = "You are heading NORTH-NORTH-EAST!";
else if (56.25 < heading <= 78.75) compass_heading = "You are heading EAST-SOUTH-EAST!";
else if (101.25 < heading <= 123.75) compass_heading = "You are heading EAST-SOUTH-EAST!";
else if (146.25 < heading <= 168.75) compass_heading = "You are heading SOUTH-SOUTH-EAST!";
else if (191.25 < heading <= 213.75) compass_heading = "You are heading SOUTH-SOUTH-WEST!";
else if (236.25 < heading <= 258.75) compass_heading = "You are heading WEST-SOUTH-WEST!";
else if (281.25 < heading <= 303.75) compass_heading = "You are heading WEST-NORTH-WEST!";
else if (326.25 < heading <= 348.75) compass_heading = "You are heading NORTH-NORTH-WEST!";
Serial.print("\r\n");
Serial.println(String("---------------------------------------------------------------------------------------------------------"));
Serial.println(String("Temperature is: ") + String(temp_value) + String(" C"));
Serial.println(String("Compensated Temperature is: ") + String(comp_temp) + String(" C"));
Serial.println(String("Humidity is: ") + String(hum_value) + String(" %"));
Serial.println(String("Compensated Humidity is: ") + String(comp_hum) + String(" %"));
Serial.println(String("Pressure: ") + String(pressure_value) + String(" hPa"));
Serial.println(String("Altitude: ") + String(altitude) + String(" m"));
Serial.println(String("Relative Humidity: ") + String(relative_humidity) + String(" %"));
Serial.println(String("Air Dew Point: ") + String(air_dew_point) + String(" C"));
Serial.println(String("Air Dew Point Accurate: ") + String(air_dew_point_accurate) + String(" C"));
Serial.println(String("Saturation Vapor Pressure: ") + String(saturation_vapor_pressure));
Serial.println(String("Water Vapor Pressure: ") + String(water_vapor_pressure) + String(" hPa"));
Serial.println(String("Dry Air Pressure ") + String(dry_air_pressure) + String(" hPa"));
Serial.println(String("Air Density: ") + String(air_density) + String(" kg/m^3"));
Serial.println(String("Absolute Humidity: ") + String(absolute_humidity, 4) + String(" kg/m^3"));
Serial.println(String("Cloud Base Altitude Method 1: ") + String(cloud_base_altitude_method1, 4) + String(" m"));
Serial.println(String("Cloud Base Altitude Method 2: ") + String(cloud_base_altitude_method2, 4) + String(" ft"));
Serial.println(String("Cloud Base Temperature: ") + String(cloud_base_temperature));
Serial.println(String("Heat Index: ") + String(heat_index));
Serial.println(String("Discomfort level: ") + String(discomfort_index));
Serial.println(discomfort_condition);
Serial.println(pressure_effect);
Serial.println(String("Gas resistance: ") + String(gas_resistance));
Serial.println(String("Compensated Gas Resistance is: ") + String(comp_gas_res) + String(" Ohms"));
Serial.println(String("Temperature Fusion is: ") + String(temp_fusion) + String(" C"));
Serial.println(String("Humidity Fusion is: ") + String(humidity_fusion) + String(" %"));
Serial.println(String("Volatile Organic: ") + String(voc_eq) + String(" ppm"));
Serial.println(voc_air_quality);
Serial.println(String("Estimation of CO2 levels: ") + String(co2_eq) + String(" ppm"));
Serial.println(co2_air_quality);
Serial.println(String("Air Quality Index is: ") + String(iaq));
Serial.println(String("IAQ Accuracy Level: ") + String(accuracy));
Serial.println(iaq_air_quality);
Serial.println(String("Tilt info: ") + tilt.toString() + String(" - Binary value:") + tilt.value());
Serial.println(String(compass_heading) + String(" Heading Angle: ") + String(heading));
Serial.println(String("Compass Roll/Tilt: ") + String(roll, 2));
Serial.println(String("---------------------------------------------------------------------------------------------------------"));
}
}
void string_separator(String str, String strs[], int result) { //split the string into substrings, second value
memset(strs, 0, sizeof(strs)); //reset char array to empty values
StringCount = 0; //reset string index to 0
while (str.length() > 6)
{
int index = str.indexOf(' ');
if (index == -1) // No space found
{
strs[StringCount++] = str;
break;
}
else
{
strs[StringCount++] = str.substring(0, index);
str = str.substring(index + 1);
}
}
if (result == 1)
{
for (int i = 0; i < StringCount; i++)
{
Serial.print(String("[") + String(i) + String("] = "));
Serial.print(strs[i]);
Serial.print("\r\n");
}
}
}
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