Celsius to Fahrenheit Conversion with HTU21DF



  • I am building a humidity controller using the humidity and temperature sensor. So far everything is working correctly but I was wondering how I could get the temperature to read back in Fahrenheit rather than Celsius. I know the formula is 9/5*C+32=F but I don't know exactly how to get this to work with my code.

    Here is the code I have written:
    Code: [Select]

    #include <Wire.h>
    #include "Adafruit_HTU21DF.h"

    Adafruit_HTU21DF htu = Adafruit_HTU21DF ();

    int ledPin = 13;
    int relayPin = 9;

    void setup() {

    pinMode (ledPin, OUTPUT);
    pinMode (relayPin, OUTPUT);
    Serial.begin(9600);
    Serial.println("HTU21DF Humidity Controller");

    if (!htu.begin()) {
    Serial.println("Couldn't find sensor!");
    }
    }

    void loop() {

    if (htu.readHumidity()>=75) {
    Serial.print("Humidifier Off");
    digitalWrite(ledPin, LOW);
    digitalWrite(relayPin, LOW);
    Serial.print("\t\tTemp: "); Serial.print(htu.readTemperature());
    Serial.print("\t\tHum: "); Serial.println(htu.readHumidity());
    }

    else {
    Serial.print("Humidifier On");
    digitalWrite(ledPin, HIGH);
    digitalWrite(relayPin, HIGH);
    Serial.print("\t\tTemp: "); Serial.print(htu.readTemperature());
    Serial.print("\t\tHum: "); Serial.println(htu.readHumidity());
    }

    delay(1000);

    }
    This is the section of the file "Adafruit_HTU21DF.cpp" that deals with temperature:

    Code: [Select]

    float Adafruit_HTU21DF::readTemperature(void) {

    // OK lets ready!
    Wire.beginTransmission(HTU21DF_I2CADDR);
    Wire.write(HTU21DF_READTEMP);
    Wire.endTransmission();

    delay(50); // add delay between request and actual read!

    Wire.requestFrom(HTU21DF_I2CADDR, 3);
    while (!Wire.available()) {}

    uint16_t t = Wire.read();
    t <<= 8;
    t |= Wire.read();

    uint8_t crc = Wire.read();

    float temp = t;
    temp *= 175.72;
    temp /= 65536;
    temp -= 46.85;

    return temp;
    }


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