library HTU21D results in float

Dependents:   HTU21D_HELLOWORLD Major_dHome

Fork of HTU21D by Alex Lipford

HTU21D/HTU21D.cpp

Committer:
hwing91
Date:
2014-03-28
Revision:
0:db86ad1b4459
Child:
1:d7568a103ef5

File content as of revision 0:db86ad1b4459:

/**
 * @author Alan Lai & Nelson Diaz
 * The Georgia Institute of Technology 
 * ECE 4180 Embeded Systems
 * Professor Hamblen
 * 03/28/2014
 * 
 * @section LICENSE
 * ----------------------------------------------------------------------------
 * "THE BEER-WARE LICENSE" (Revision 42):
 * <alanhlai91@gmail.com> wrote this file. As long as you retain this notice you
 * can do whatever you want with this stuff. If we meet some day, and you think
 * this stuff is worth it, you can buy me a beer in return.
 * ----------------------------------------------------------------------------
 *
 *
 * @section DESCRIPTION
 *
 * HTU21D Humidity and Temperature sensor.
 *
 * Datasheet, specs, and information:
 *
 * https://www.sparkfun.com/products/12064
 */

/**
 * Includes
 */
#include "HTU21D.h"

HTU21D::HTU21D(PinName sda, PinName scl) {

    i2c_ = new I2C(sda, scl);
    //400KHz, as specified by the datasheet.
    i2c_->frequency(400000);



}

int HTU21D::sample_ctemp(void) {

    char tx[1];
    char rx[2];

    tx[0] = TRIGGER_TEMP_MEASURE; // Triggers a temperature measure by feeding correct opcode.
    i2c_->write((HTU21D_I2C_ADDRESS << 1) & 0xFE, tx, 1);
    wait_ms(1);
    
    // Reads triggered measure
    i2c_->read((HTU21D_I2C_ADDRESS << 1) | 0x01, rx, 2);
    wait_ms(1);
    
    // Algorithm from datasheet to compute temperature.
    unsigned int rawTemperature = ((unsigned int) rx[0] << 8) | (unsigned int) rx[1];
    rawTemperature &= 0xFFFC;

    float tempTemperature = rawTemperature / (float)65536; //2^16 = 65536
    float realTemperature = -46.85 + (175.72 * tempTemperature); //From page 14

    return (int)realTemperature;

}

int HTU21D::sample_ftemp(void){
    int temptemp = sample_ctemp();
    int ftemp = temptemp * 1.8 + 32;
    
    return ftemp;
}

int HTU21D::sample_ktemp(void){
    int temptemp = sample_ctemp();
    int ktemp = temptemp + 274;
    
    return ktemp;
    
    
}

int HTU21D::sample_humid(void) {

    char tx[1];
    char rx[2];


    tx[0] = TRIGGER_HUMD_MEASURE; // Triggers a humidity measure by feeding correct opcode.
    i2c_->write((HTU21D_I2C_ADDRESS << 1) & 0xFE, tx, 1);
    wait_ms(1);
    
    // Reads triggered measure
    i2c_->read((HTU21D_I2C_ADDRESS << 1) | 0x01, rx, 2);
    wait_ms(1);
    
    //Algorithm from datasheet.
    unsigned int rawHumidity = ((unsigned int) rx[0] << 8) | (unsigned int) rx[1];

    rawHumidity &= 0xFFFC; //Zero out the status bits but keep them in place
    
    //Given the raw humidity data, calculate the actual relative humidity
    float tempRH = rawHumidity / (float)65536; //2^16 = 65536
    float rh = -6 + (125 * tempRH); //From page 14


    return (int)rh;

}