sht.c

// Sensirion SHT Sensor

#include <io430.h>

#include <intrinsics.h>

#include "sht.h"

#include "delay.h"

#define SHTDIR P5DIR

#define SHTOUT P5OUT

#define SHTIN P5IN

#define PIN_CLK 0x40

#define PIN_DAT 0x80

#define SHT_CMD_TEMP    0x03

#define SHT_CMD_HUMID   0x05

#define SHT_CMD_WR_STAT 0x06

#define SHT_CMD_RD_STAT 0x07

#define SHT_CMD_RESET   0x1E

#define SHT_VOLTAGE_COMPENSATION_D1_5V   -40.1

#define SHT_VOLTAGE_COMPENSATION_D1_4V   -39.8

#define SHT_VOLTAGE_COMPENSATION_D1_3_5V -39.7

#define SHT_VOLTAGE_COMPENSATION_D1_3_3V -39.7

#define SHT_VOLTAGE_COMPENSATION_D1_3V   -39.6

#define SHT_VOLTAGE_COMPENSATION_D1_2_5V -39.4

#define SHT_VOLTAGE_COMPENSATION_D1 SHT_VOLTAGE_COMPENSATION_D1_3_3V

#define NOP __no_operation()

inline static char sht_getdat(void)

{

  NOP;

  return (SHTIN&PIN_DAT);

}

inline static void sht_setdat(unsigned char c)

{

  if (c) SHTDIR&=~PIN_DAT; // bei 1 Pullup wirken lassen

  else   SHTDIR|=PIN_DAT;  // ansonsten auf Ausgang schalten,

                           // wo eine 0 ausgegeben wird

  NOP;

}

inline static void sht_clkhi(void)

{

  SHTOUT|=PIN_CLK;

  NOP;

}

inline static void sht_clklo(void)

{

  SHTOUT&=~PIN_CLK;

  NOP;

}

void sht_init(void)

{

  SHTDIR|=PIN_CLK;

  SHTDIR&=~PIN_DAT;

  SHTOUT&=~(PIN_CLK|PIN_DAT);

  delayms(50); // Power Up Delay

}

static void sht_start(void)

{

  int i;

  sht_setdat(1);

  for (i=0;i<10;i++)

  {

    sht_clkhi();

    sht_clklo();

  }

  sht_clkhi();

  sht_setdat(0);

  sht_clklo();

  sht_clkhi();

  sht_setdat(1);

  sht_clklo();

}

static void sht_sendbyte(unsigned char c)

{

  int i;

  // Datenbits rausschieben

  for (i=8;i>0;--i)

  {

    sht_setdat(c&0x80);

    sht_clkhi();

    sht_clklo();

    c<<=1;

  }

  // Ack empfangen

  sht_setdat(1);

  sht_clkhi();

  sht_clklo();

//  while(sht_getdat());

}

static unsigned char sht_recvbyte_msb(unsigned char a)

{

  int i;

  unsigned char c;

  sht_setdat(1);

  // Datenbits reinschieben

  for (i=8;i>0;--i)

  {

    c<<=1;

    sht_clkhi();

    if (sht_getdat()) c|=1;

    sht_clklo();

  }

  // Ack senden

  sht_setdat(a);

  sht_clkhi();

  sht_clklo();

  sht_setdat(1);

  return c;

}

static unsigned char sht_recvbyte_lsb(unsigned char a)

{

  int i;

  unsigned char c;

  sht_setdat(1);

  // Datenbits reinschieben

  for (i=8;i>0;--i)

  {

    c>>=1;

    sht_clkhi();

    if (sht_getdat()) c|=128;

    sht_clklo();

  }

  // Ack senden

  sht_setdat(a);

  sht_clkhi();

  sht_clklo();

  sht_setdat(1);

  return c;

}

static unsigned char sht_crc(unsigned char crc, unsigned char data)

{

  static const unsigned char crctab[]={

      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

  };

  return crctab[crc^data];

}

unsigned short sht_measure(char is_rh)

{

  int i;

  unsigned short s;

  unsigned char cmd,ch,cl,crc;

  unsigned char mycrc;

  sht_start();

  if (is_rh) cmd=SHT_CMD_HUMID;

  else       cmd=SHT_CMD_TEMP;

  sht_sendbyte(cmd);

  delayms(5);

  sht_setdat(1);

  for (i=0;i<1024;i++)

  {

    if(sht_getdat()==0) break;

    delayms(5);

  }

  if (sht_getdat()) return 0xfffe;

  ch=sht_recvbyte_msb(0);

  cl=sht_recvbyte_msb(0);

  crc=sht_recvbyte_lsb(1);

  s=((unsigned short)ch<<8)+(unsigned short)cl;

  mycrc=sht_crc(0,cmd);

  mycrc=sht_crc(mycrc,ch);

  mycrc=sht_crc(mycrc,cl);

  if (mycrc!=crc) s=0xffff;

  return s;

}

// temp is returned in two-digit fixedpoint (celsius*100)

short sht_convert_temp(unsigned short raw_temp)

{

  return ((short)raw_temp+(((short)SHT_VOLTAGE_COMPENSATION_D1)*100));

}

// humidity is returned in one-digit fixedpoint (RH percent*10)

unsigned short sht_convert_humid(unsigned short raw_temp,unsigned short raw_humid)

{

  unsigned long humid;

  /**** first step: relative humidity ****/

  // constants from datasheet (values for V4 sensors), shifted and adapted

  const unsigned long c1 = (unsigned long)((2.0468 * 100 * (1L<<18))+0.5);

  const unsigned long c2 = (unsigned long)((0.0367 * 100 * (1L<<18))+0.5);

  const unsigned long c3 = (unsigned long)((1.5955e-6 * 100 * (1L<<27))+0.5);

  // uncompensated = c2*raw - (c3 * raw * raw) - c1

  humid = (c2 * (unsigned long)raw_humid) \

        - (((((unsigned long)raw_humid * (unsigned long)raw_humid) >> 7) * c3) >> 2) \

        - c1;

  // humid >> 18 would now be the uncompensated humidity in RH% * 100

  /**** second step: temperature compensation ****/

  // constants from datasheet, shifted and adapted

  const long t1 = (long)((0.01 * 100 * (1L<<18))+0.5);

  const long t2 = (long)((0.00008 * 100 * (1L<<18))+0.5);

  // humid += (temp-25) * (t1 + t2*raw_temp)

  humid += (long)((sht_convert_temp(raw_temp)/100)-25) \

           * (t1 + (t2 * (long)raw_humid));

  // humid >> 18 now is the real humidity in RH% * 100

  // shift it back and round to RH% * 10

  // (the sensor doesn't really provide enough accuracy to justify more resolution)

  return (unsigned short)(((humid >> 18)+5)/10);

}