Temerature Humidity Sensor DHT11 with Explore M3

    DHT11 is super inexpensive, not that accurate digital temperature and Humidity Sensory. It uses single pin to communicate with Explore M3. Let's display the parameters then on a display!

    Hookup and Demo

    • DHT11 uses a single pin which is connected to PIN 2 of Explore M3

    Dht11 ExploreM3.JPG

    Code

    //
    // FILE: dht11_test1.pde
    // PURPOSE: DHT11 library test sketch for Arduino
    //
    #include <dht11.h>
    #include "ST7565.h"
    //Celsius to Fahrenheit conversion
    double Fahrenheit(double celsius)
    {
    return 1.8 * celsius + 32;
    }
    // fast integer version with rounding
    //int Celcius2Fahrenheit(int celcius)
    //{
    // return (celsius * 18 + 5)/10 + 32;
    //}
    //Celsius to Kelvin conversion
    double Kelvin(double celsius)
    {
    return celsius + 273.15;
    }
    // dewPoint function NOAA
    // reference (1) : http://wahiduddin.net/calc/density_algorithms.htm
    // reference (2) : http://www.colorado.edu/geography/weather_station/Geog_site/about.htm
    //
    double dewPoint(double celsius, double humidity)
    {
    // (1) Saturation Vapor Pressure = ESGG(T)
    double RATIO = 373.15 / (273.15 + celsius);
    double RHS = -7.90298 * (RATIO - 1);
    RHS += 5.02808 * log10(RATIO);
    RHS += -1.3816e-7 * (pow(10, (11.344 * (1 - 1/RATIO ))) - 1) ;
    RHS += 8.1328e-3 * (pow(10, (-3.49149 * (RATIO - 1))) - 1) ;
    RHS += log10(1013.246);
    // factor -3 is to adjust units - Vapor Pressure SVP * humidity
    double VP = pow(10, RHS - 3) * humidity;
    // (2) DEWPOINT = F(Vapor Pressure)
    double T = log(VP/0.61078); // temp var
    return (241.88 * T) / (17.558 - T);
    }
    // delta max = 0.6544 wrt dewPoint()
    // 6.9 x faster than dewPoint()
    // reference: http://en.wikipedia.org/wiki/Dew_point
    double dewPointFast(double celsius, double humidity)
    {
    double a = 17.271;
    double b = 237.7;
    double temp = (a * celsius) / (b + celsius) + log(humidity*0.01);
    double Td = (b * temp) / (a - temp);
    return Td;
    }
    ST7565 glcd(29, 28, 27, 26, 25);
    dht11 DHT11;
    #define DHT11PIN 2
    void setup()
    {
    Serial.begin(115200);
    Serial.println("DHT11 TEST PROGRAM ");
    Serial.print("LIBRARY VERSION: ");
    Serial.println(DHT11LIB_VERSION);
    Serial.println();
    glcd.begin(0x18);
    // draw a string at location (0,0)
    // glcd.drawstring(0, 0, " Welcome to Explore Embedded");
    // glcd.display();
    }
    void loop()
    {
    Serial.println("\n");
    int chk = DHT11.read(DHT11PIN);
    glcd.drawstring(0, 0, " Read sensor: " );
    glcd.display();
    //Serial.print("Read sensor: ");
    switch (chk)
    {
    case DHTLIB_OK:
    glcd.drawstring(70, 0, " OK" );
    glcd.display();
    //Serial.println("OK");
    break;
    case DHTLIB_ERROR_CHECKSUM:
    Serial.println("Checksum error");
    break;
    case DHTLIB_ERROR_TIMEOUT:
    Serial.println("Time out error");
    break;
    default:
    Serial.println("Unknown error");
    break;
    }
    //Serial.print("Humidity (%): ");
    glcd.drawstring(0, 2, " Humidity (%): " );
    glcd.drawNumFloat(90,2,DHT11.humidity,2);
    glcd.display();
    // Serial.println((float)DHT11.humidity, 2);
    //Serial.print("Temp (°C): ");
    glcd.drawstring(0, 4, " Temp (C) : " );
    glcd.drawNumFloat(90,4,DHT11.temperature,2);
    glcd.display();
    //Serial.println((float)DHT11.temperature, 2);
    delay(2000);
    }
    //
    // END OF FILE
    //
    view raw dht11_exploreM3.ino hosted with ❤ by GitHub

    References

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