File content as of revision 1:c9ef27da97b5:

#ifndef SI7021_H
#define SI7021_H

#include "mbed.h"

/** Si7012 Read Temperature Command */
#define READ_TEMP        0xE0 /* Read previous T data from RH measurement command*/
/** Si7012 Read RH Command */
#define READ_RH          0xE5 /* Perform RH (and T) measurement. */

/** Si7012 Read ID */
#define READ_ID1_1       0xFA
#define READ_ID1_2       0x0F
#define READ_ID2_1       0xFC
#define READ_ID2_2       0xC9

/** Si7012 Read Firmware Revision */
#define READ_FWREV_1     0x84
#define READ_FWREV_2     0xB8

/** I2C device address for Si7021 */
#define ADDR    0x80

/** I2C device frequency for Si7021 */
#define FREQ    100000

/** Device ID value for Si7021 */
#define DEVICE_ID 0x15

class Si7021
{
public:
    Si7021(PinName sda, PinName scl);
    ~Si7021();
    
    /*
     * Get last measured temperature data
     * return: int32_t = temperature in millidegrees centigrade
     */
    int32_t get_temperature();

    /*
     * Get last measured relative humidity data
     * return: uint32_t = relative humidity value in milli-percent
     */
    uint32_t get_humidity();
    
    /*
     * Perform measurement.
     * Asynchronous callback can be provided (type void (*)(void)).
     * return: 0 if successful, else one of the defined error codes.
     */
    bool measure();
    
    /*
     * Check if the sensor is active and responding. This will update the get_active value.
     * Asynchronous callback can be provided (type void (*)(void)).
     * return: 0 if successful, else one of the defined error codes.
     */
    bool check();
    
private:
    I2C i2c;
    
    uint8_t  rx_buff[8];
    uint8_t  tx_buff[2];

    uint32_t rhData;
    int32_t  tData;
};

#endif
Si7021::Si7021(PinName sda, PinName scl):i2c(sda, scl)
{
    i2c.frequency(FREQ);
}

Si7021::~Si7021()
{
    
}

int32_t Si7021::get_temperature()
{
    return tData;
}

uint32_t Si7021::get_humidity()
{
    return rhData;
}

bool Si7021::measure()
{
    tx_buff[0] = READ_RH;
    if(i2c.write(ADDR, (char*)tx_buff, 1) != 0) return 0;
    if(i2c.read(ADDR, (char*)rx_buff, 2) != 0) return 0;
    
    rhData = ((uint32_t)rx_buff[0] << 8) + (rx_buff[1] & 0xFC);
    rhData = (((rhData) * 15625L) >> 13) - 6000;
    
    tx_buff[0] = READ_TEMP;
    if(i2c.write(ADDR, (char*)tx_buff, 1) != 0) return 0;
    if(i2c.read(ADDR, (char*)rx_buff, 2) != 0) return 0;
    
    tData = ((uint32_t)rx_buff[0] << 8) + (rx_buff[1] & 0xFC);
    tData = (((tData) * 21965L) >> 13) - 46850;
    
    return 1;
}

bool Si7021::check()
{
    tx_buff[0] = READ_ID2_1;
    tx_buff[1] = READ_ID2_2;
    if(i2c.write(ADDR, (char*)tx_buff, 2) != 0) return 0;
    if(i2c.read(ADDR, (char*)rx_buff, 8) != 0) return 0;
    
    if(rx_buff[0] == DEVICE_ID)
        return true;
    else return 0;
}