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/////////////////////////////////////////////////////////////////////////////// |
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/////////////////////////////////////////////////////////////////////////////// |
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//#define sht_data_pin PIN_D0 |
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//#define sht_data_pin PIN_D0 |
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//#define sht_clk_pin PIN_D1 |
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//#define sht_clk_pin PIN_D1 |
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#include <math.h> |
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#define noACK 0 |
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#define ACK 1 |
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//adr command r/w |
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#define STATUS_REG_W 0x06 //000 0011 0 |
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#define STATUS_REG_R 0x07 //000 0011 1 |
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#define MEASURE_TEMP 0x03 //000 0001 1 |
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#define MEASURE_HUMI 0x05 //000 0010 1 |
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#define RESET 0x1e //000 1111 0 |
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//***** Function to alert SHT75 ***** |
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//***** Function to alert SHT75 ***** |
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// generates a transmission start |
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// generates a transmission start |
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// _____ ________ |
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// _____ ________ |
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// DATA: |_______| |
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// DATA: |_______| |
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// communication reset: DATA-line=1 and at least 9 SCK cycles followed by transstart |
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// communication reset: DATA-line=1 and at least 9 SCK cycles followed by transstart |
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// _____________________________________________________ ________ |
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// _____________________________________________________ ________ |
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// DATA: |_______| |
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// DATA: |_______| |
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// _ _ _ _ _ _ _ _ _ ___ ___ |
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// _ _ _ _ _ _ _ _ _ ___ ___ |
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// SCK : __| |__| |__| |__| |__| |__| |__| |__| |__| |______| |___| |______ |
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// SCK : __| |__| |__| |__| |__| |__| |__| |__| |__| |______| |___| |______ |
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void sht_comreset (void) |
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void sht_comreset (void) |
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{ |
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{ |
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int8 i; |
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int8 i; |
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output_float(sht_data_pin); //data high |
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output_float(sht_data_pin); //data high |
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sht_comreset(); //SHT75 communication reset |
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sht_comreset(); //SHT75 communication reset |
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sht_comwrite(0x1e); //send SHT75 reset command |
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sht_comwrite(0x1e); //send SHT75 reset command |
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delay_ms(15); //pause 15 ms |
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delay_ms(15); //pause 15 ms |
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} |
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} |
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//---------------------------------------------------------------------------------- |
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char sht_write_statusreg(unsigned char *p_value) |
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//---------------------------------------------------------------------------------- |
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// writes the status register with checksum (8-bit) |
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{ |
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unsigned char error=0; |
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sht_comstart(); //transmission start |
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error+=sht_comwrite(STATUS_REG_W);//send command to sensor |
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error+=sht_comwrite(*p_value); //send value of status register |
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return error; //error>=1 in case of no response form the sensor |
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} |
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//***** Function to measure SHT75 temperature ***** |
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//***** Function to measure SHT75 temperature ***** |
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int16 sht_measuretemp (void) |
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int16 sht_measuretemp (void) |
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{ |
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{ |
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//***** Function to calculate SHT75 temp & RH ***** |
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//***** Function to calculate SHT75 temp & RH ***** |
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void calculate_data (int16 temp, int16 humid, float & tc, float & rhlin, float & rhtrue) |
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void calculate_data (int16 temp, int16 humid, float & tc, float & rhlin, float & rhtrue) |
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{ |
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{ |
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const float C1=-2.0468; // for 12 Bit RH |
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const float C2=+0.0367; // for 12 Bit RH |
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const float C3=-0.0000015955; // for 12 Bit RH |
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const float T1=+0.01; // for 12 Bit RH |
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const float T2=+0.00008; // for 12 Bit RH |
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float rh; |
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float rh; |
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//calculate temperature reading |
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//calculate temperature reading |
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tc = ((float) temp * 0.01) - 40.0; |
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tc = ((float) temp * 0.01) - 40.0; |
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//calculate Real RH reading |
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//calculate Real RH reading |
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rh = (float) humid; |
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rh = (float) humid; |
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rhlin = (rh * 0.0405) - (rh * rh * 0.0000028) - 4.0; |
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rhlin = C1 + (rh * C2) + (rh * rh * C3); |
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//calculate True RH reading |
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//calculate True RH reading |
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rhtrue = ((tc - 25.0) * (0.01 + (0.00008 * rh))) + rhlin; |
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rhtrue = ((tc - 25.0) * (0.01 + (0.00008 * rh))) + rhlin; |
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if(rhtrue>99)rhtrue=100; //cut if the value is outside of |
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if(rhtrue<0.1)rhtrue=0.1; //the physical possible range |
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} |
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} |
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//***** Function to measure & calculate SHT75 temp & RH ***** |
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//***** Function to measure & calculate SHT75 temp & RH ***** |
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void sht_init (void) |
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void sht_init (void) |
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{ |
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{ |
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sht_comreset(); //reset SHT75 |
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sht_comreset(); //reset SHT75 |
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delay_ms(20); //delay for power-up |
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delay_ms(20); //delay for power-up |
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} |
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} |
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//-------------------------------------------------------------------- |
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float calc_dewpoint(float h,float t) |
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//-------------------------------------------------------------------- |
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// calculates dew point |
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// input: humidity [%RH], temperature [K] |
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// output: dew point [K] |
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{ float k,dew_point ; |
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k = (log10(h)-2)/0.4343 + (17.62*t)/(243.12+t); |
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dew_point = 243.12*k/(17.62-k); |
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return dew_point; |
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} |
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