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//>>> The latest version of this code can be found at https://github.com/jcw/ !!

// Port library interface to SHT11 sensors connected via "something like I2C"

// 2009-02-16 <jcw@equi4.com> http://opensource.org/licenses/mit-license.php

// $Id$

// rewritten in C++ using the SENSIRION SHTxx Sample Code Application Note

// the CRC calculation is from the SENSIRION SHTxx CRC Application Note

#include <Ports.h>

#include "PortsSHT11.h"

#include <avr/pgmspace.h>

#include <WProgram.h>

enum {

    MEASURE_TEMP = 0x03,

    MEASURE_HUMI = 0x05,

    STATUS_REG_W = 0x06,

    STATUS_REG_R = 0x07,

    RESET        = 0x1e,

};

static uint8_t crcTab [] PROGMEM = {

    0, 49, 98, 83, 196, 245, 166, 151, 185, 136, 219, 234, 125, 76, 31, 46, 67,

    114, 33, 16, 135, 182, 229, 212, 250, 203, 152, 169, 62, 15, 92, 109, 134,

    183, 228, 213, 66, 115, 32, 17, 63, 14, 93, 108, 251, 202, 153, 168, 197,

    244, 167, 150, 1, 48, 99, 82, 124, 77, 30, 47, 184, 137, 218, 235, 61, 12,

    95, 110, 249, 200, 155, 170, 132, 181, 230, 215, 64, 113, 34, 19, 126, 79,

    28, 45, 186, 139, 216, 233, 199, 246, 165, 148, 3, 50, 97, 80, 187, 138,

    217, 232, 127, 78, 29, 44, 2, 51, 96, 81, 198, 247, 164, 149, 248, 201, 154,

    171, 60, 13, 94, 111, 65, 112, 35, 18, 133, 180, 231, 214, 122, 75, 24, 41,

    190, 143, 220, 237, 195, 242, 161, 144, 7, 54, 101, 84, 57, 8, 91, 106, 253,

    204, 159, 174, 128, 177, 226, 211, 68, 117, 38, 23, 252, 205, 158, 175, 56,

    9, 90, 107, 69, 116, 39, 22, 129, 176, 227, 210, 191, 142, 221, 236, 123,

    74, 25, 40, 6, 55, 100, 85, 194, 243, 160, 145, 71, 118, 37, 20, 131, 178,

    225, 208, 254, 207, 156, 173, 58, 11, 88, 105, 4, 53, 102, 87, 192, 241,

    162, 147, 189, 140, 223, 238, 121, 72, 27, 42, 193, 240, 163, 146, 5, 52,

    103, 86, 120, 73, 26, 43, 188, 141, 222, 239, 130, 179, 224, 209, 70, 119,

    36, 21, 59, 10, 89, 104, 255, 206, 157, 172

};

void SHT11::crcCalc(uint8_t x) {

    crc8 = pgm_read_byte(crcTab + (x ^ crc8));

}

static void dummyCRC(uint8_t) {}

// static variables, i.e. CRC can only be enabled for all SHT11 devices at once

// the code below avoids linking in any CRC code if enableCRC() is never called

uint8_t SHT11::crc8 = 0;

void (*SHT11::crcFun)(uint8_t) = &dummyCRC;

void SHT11::enableCRC() {

    SHT11::crcFun = crcCalc;

}

// idle line state is with data as input pulled high, and clock as output low

void SHT11::clock(uint8_t x) const {

    delayMicroseconds(2);

    digiWrite2(x);

    delayMicroseconds(5);

}

void SHT11::release() const {

    mode(INPUT);

    digiWrite(1);

}

uint8_t SHT11::writeByte(uint8_t value) const {

    mode(OUTPUT);

    for (uint8_t i = 0x80; i != 0; i >>= 1) {

        digiWrite(value & i);

        clock(1);

        clock(0);

    }

    release();

    clock(1);

    uint8_t error = digiRead();

    clock(0);

    crcFun(value);

    return error;

}

uint8_t SHT11::readByte(uint8_t ack) const {

    uint8_t value = 0;

    for (uint8_t i = 0x80; i != 0; i >>= 1) {

        clock(1);

        if (digiRead())

            value |= i;

        clock(0);

    }

    mode(OUTPUT);

    digiWrite(!ack);

    clock(1);

    clock(0);

    release();

    crcFun(value);

    return value;

}

void SHT11::start() const {

    clock(0);

    mode(OUTPUT);

    digiWrite(1);

    clock(1);

    digiWrite(0);

    clock(0);

    clock(1);

    digiWrite(1);

    clock(0);

    release();

    crc8 = 0;

}

void SHT11::connReset() const {

    mode2(OUTPUT);

    clock(0);

    mode(OUTPUT);

    digiWrite(1);

    for (uint8_t i = 0; i < 9; ++i) {

        clock(1);

        clock(0);

    }

    start();

}

void SHT11::softReset() const {

    connReset();

    writeByte(RESET);

    delay(11);

}

uint8_t SHT11::readStatus() const {

    start();

    writeByte(STATUS_REG_R);

    uint8_t value = readByte(1);

    readByte(0);

    return value;

}

void SHT11::writeStatus(uint8_t value) const {

    start();

    writeByte(STATUS_REG_W);

    writeByte(value);

}

uint8_t SHT11::measure(uint8_t type, void (*delayFun)()) {

    start();

    writeByte(type == TEMP? MEASURE_TEMP : MEASURE_HUMI);

    for (uint8_t i = 0; i < 250; ++i) {

        if (!digiRead()) {

            meas[type] = readByte(1) << 8;

            meas[type] |= readByte(1);

            uint8_t flipped = 0;

            for (uint8_t j = 0x80; j != 0; j >>= 1) {

                flipped >>= 1;

                if (crc8 & j)

                    flipped |= 0x80;

            }

            if (readByte(0) != flipped)

                break;

            return 0;

        }

        if (delayFun)

            delayFun();

        else

            delay(1);

    }

    connReset();

    return 1;

}

#ifndef __AVR_ATtiny84__

void SHT11::calculate(float& rh_true, float& t_C) const {

    const float C1=-2.0468;

    const float C2= 0.0367;

    const float C3=-1.5955e-6;

    const float T1=0.01;

    const float T2=0.00008;

    t_C = meas[TEMP] * 0.01 - 39.66;  // for 3.3 V

    float rh = meas[HUMI];

    rh_true = (t_C-25)*(T1+T2*rh) + C3*rh*rh + C2*rh + C1;

    if (rh_true > 99) rh_true = 100;

    if (rh_true < 0.1) rh_true = 0.1;

}

float SHT11::dewpoint(float h, float t) {

    float k = (log10(h)-2)/0.4343 + (17.62*t)/(243.12+t);

    return 243.12*k/(17.62-k);

}

#else

//XXX TINY!

#endif