Suga koubou / SHT1x

mbed library to use a SENSIRION SHT1x/SHT7x sensor humidity and temperature

SHT1x.cpp@0:ad72ec3d85e8, 2012-06-21 (annotated)

Committer:
okini3939
Date:
Thu Jun 21 03:56:43 2012 +0000
Revision:
0:ad72ec3d85e8

        

        
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/*





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 * mbed library to use a SENSIRION SHT1x/SHT7x sensor





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 * Copyright (c) 2011 Hiroshi Suga





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 * Released under the MIT License: http://mbed.org/license/mit





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 */





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/** @file





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 * @brief mbed library to use a SENSIRION SHT1x/SHT7x sensor





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 * humidity/temperature sensor SHT11, SHT15, SHT71, SHT75 (SENSIRION) Ver.4





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 * interface: I2C digital





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 */





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#include "mbed.h"





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#include "SHT1x.h"





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enum SHT_cmd {





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    SHT_cmd_temperature = 0x03,





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    SHT_cmd_humidity = 0x05,





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    SHT_cmd_read_status = 0x07,





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    SHT_cmd_write_status = 0x06,





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    SHT_cmd_reset = 0x1e





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};





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SHT1x::SHT1x (PinName p_sda, PinName p_scl, SHT_acc p_acc, SHT_vdd p_vdd) : i2c(p_sda, p_scl) {





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    init(p_acc, p_vdd);





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}





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SHT1x::SHT1x (I2C& p_i2c, SHT_acc p_acc, SHT_vdd p_vdd) : i2c(p_i2c) {





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    init(p_acc, p_vdd);





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}





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float SHT1x::get_temperature() {





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    return temperature;





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}





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float SHT1x::get_humidity() {





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    return humidity;





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}





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void SHT1x::update () {





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    float t, rhl, rht;





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    unsigned short sot, sorh;





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    sot = twi_readshort(SHT_cmd_temperature, (accuracy == SHT_low ? 80 : 320));





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    sorh = twi_readshort(SHT_cmd_humidity, (accuracy == SHT_low ? 20 : 80));





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    if (sot == 0xffff || sorh == 0xffff) return;





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    if (accuracy == SHT_low) {





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        sot &= 0x0fff; // 12bit





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        sorh &= 0x00ff; // 8bit





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    } else {





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        sot &= 0x3fff; // 14bit





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        sorh &= 0x0fff; // 12bit





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    }    





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    t = d1 + d2 * (float)sot;





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    temperature = t;





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    rhl = c1 + c2 * (float)sorh + c3 * (float)(sorh * sorh);





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    rht = (t - 25.0) * (t1 + t2 * (float)sorh) + rhl;





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    if (rht > 99.0) rht = 100.0;





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    humidity = rht;





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}





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void SHT1x::init (SHT_acc p_acc, SHT_vdd p_vdd) {





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    humidity = 0;





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    temperature = 0;





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    if (p_vdd == SHT_3V3) {





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        d1 = -39.66; // 3.3V





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    } else {





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        d1 = -40.1; // 5V





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    }





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    accuracy = p_acc;





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    if (accuracy == SHT_low) {





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        d2 = 0.04;





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        c1 = -2.0468; c2 = 0.5872; c3 = -4.0845/10000.0;





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        t1 = 0.01; t2 = 0.00128;





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        twi_writechar(SHT_cmd_write_status, 1);





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    } else {





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        d2 = 0.01;





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        c1 = -2.0468; c2 = 0.0367; c3 = -1.5955/1000000.0;





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        t1 = 0.01; t2 = 0.00008;





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        twi_writechar(SHT_cmd_write_status, 0);





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    }    





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}





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unsigned short SHT1x::twi_readshort (int addr, int wait) {





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    unsigned short i;





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    i2c.start();





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    i2c.stop();





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    i2c.start();





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    i2c.write(addr);





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    wait_ms(wait);





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    i = i2c.read(1) << 8;





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    i |= i2c.read(1);





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    i2c.read(0);





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    i2c.stop();





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    return i;





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}





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void SHT1x::twi_writechar (int addr, int dat) {





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    i2c.start();





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    i2c.stop();





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    i2c.start();





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    i2c.write(addr);





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    i2c.write(dat);





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    i2c.stop();





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}