Rev Author Line No. Line
2779 kaklik 1 ///////////////////////////////////////////////////////////////////////////////
2 // //
2836 kaklik 3 // Driver file for SHT1x Temperature & Humidity Sensor //
2779 kaklik 4 // //
2836 kaklik 5 // ***** To initialise SHT1x sensor upon power up ***** //
2779 kaklik 6 // //
7 // Function : sht_init() //
8 // Return : none //
9 // //
10 // //
11 // ***** To measure and caluculate SHT75 temp & real RH ***** //
12 // //
13 // Function : sht_rd (temp, truehumid) //
14 // Return : temperature & true humidity in float values //
15 // //
16 ///////////////////////////////////////////////////////////////////////////////
17  
18 //#define sht_data_pin PIN_D0
19 //#define sht_clk_pin PIN_D1
20  
2837 kaklik 21 #include <math.h>
2779 kaklik 22  
2837 kaklik 23  
24 #define noACK 0
25 #define ACK 1
26 //adr command r/w
27 #define STATUS_REG_W 0x06 //000 0011 0
28 #define STATUS_REG_R 0x07 //000 0011 1
29 #define MEASURE_TEMP 0x03 //000 0001 1
30 #define MEASURE_HUMI 0x05 //000 0010 1
31 #define RESET 0x1e //000 1111 0
32  
2779 kaklik 33 //***** Function to alert SHT75 *****
2836 kaklik 34 // generates a transmission start
35 // _____ ________
36 // DATA: |_______|
37 // ___ ___
38 // SCK : ___| |___| |______
2779 kaklik 39  
2836 kaklik 40 void sht_comstart (void)
2779 kaklik 41 {
42 output_float(sht_data_pin); //data high
43 output_low(sht_clk_pin); //clk low
44 delay_us(2);
45 output_high(sht_clk_pin); //clk high
46 delay_us(2);
47 output_low(sht_data_pin); //data low
48 delay_us(2);
49 output_low(sht_clk_pin); //clk low
50 delay_us(5);
51 output_high(sht_clk_pin); //clk high
52 delay_us(2);
53 output_float(sht_data_pin); //data high
54 delay_us(2);
55 output_low(sht_clk_pin); //clk low
56 }
57  
58  
59 //***** Function to write data to SHT75 *****
60  
2836 kaklik 61 int1 sht_comwrite (int8 iobyte)
2779 kaklik 62 {
63 int8 i, mask = 0x80;
64 int1 ack;
65  
66 //Shift out command
67 delay_us(5);
68 for(i=0; i<8; i++)
69 {
70 output_low(sht_clk_pin); //clk low
71 if((iobyte & mask) > 0) output_float(sht_data_pin); //data high if MSB high
72 else output_low(sht_data_pin); //data low if MSB low
73 delay_us(2);
74 output_high(sht_clk_pin); //clk high
75 delay_us(2);
76 mask = mask >> 1; //shift to next bit
77 }
78  
79 //Shift in ack
80 output_low(sht_clk_pin); //clk low
81 delay_us(2);
82 ack = input(sht_data_pin); //get ack bit
83 output_high(sht_clk_pin); //clk high
84 delay_us(2);
85 output_low(sht_clk_pin); //clk low
86 return(ack);
87 }
88  
89  
90 //***** Function to read data from SHT75 *****
91  
2836 kaklik 92 int16 sht_comread (void)
2779 kaklik 93 {
94 int8 i;
95 int16 iobyte = 0;
96 const int16 mask0 = 0x0000;
97 const int16 mask1 = 0x0001;
98  
99 //shift in MSB data
100 for(i=0; i<8; i++)
101 {
102 iobyte = iobyte << 1;
103 output_high(sht_clk_pin); //clk high
104 delay_us(2);
105 if (input(sht_data_pin)) iobyte |= mask1; //shift in data bit
106 else iobyte |= mask0;
107 output_low(sht_clk_pin); //clk low
108 delay_us(2);
109 }
110  
111 //send ack 0 bit
112 output_low(sht_data_pin); //data low
113 delay_us(2);
114 output_high(sht_clk_pin); //clk high
115 delay_us(5);
116 output_low(sht_clk_pin); //clk low
117 delay_us(2);
118 output_float(sht_data_pin); //data high
119  
120 //shift in LSB data
121 for(i=0; i<8; i++)
122 {
123 iobyte = iobyte << 1;
124 output_high(sht_clk_pin); //clk high
125 delay_us(2);
126 if (input(sht_data_pin)) iobyte |= mask1; //shift in data bit
127 else iobyte |= mask0;
128 output_low(sht_clk_pin); //clk low
129 delay_us(2);
130 }
131  
132 //send ack 1 bit
133 output_float(sht_data_pin); //data high
134 delay_us(2);
135 output_high(sht_clk_pin); //clk high
136 delay_us(5);
137 output_low(sht_clk_pin); //clk low
138  
139 return(iobyte);
140 }
141  
142  
143 //***** Function to wait for SHT75 reading *****
144  
2836 kaklik 145 void sht_comwait (void)
2779 kaklik 146 {
147 int16 sht_delay;
148  
149 output_float(sht_data_pin); //data high
150 output_low(sht_clk_pin); //clk low
151 delay_us(2);
2836 kaklik 152 for(sht_delay=0; sht_delay<350; sht_delay++) // wait for max 350ms (for 14bit measurement)
2779 kaklik 153 {
154 if (!input(sht_data_pin)) break; //if sht_data_pin low, SHT75 ready
2836 kaklik 155 delay_ms(1);
2779 kaklik 156 }
157 }
158  
159  
160 //***** Function to reset SHT75 communication *****
2836 kaklik 161 // communication reset: DATA-line=1 and at least 9 SCK cycles followed by transstart
162 // _____________________________________________________ ________
163 // DATA: |_______|
164 // _ _ _ _ _ _ _ _ _ ___ ___
165 // SCK : __| |__| |__| |__| |__| |__| |__| |__| |__| |______| |___| |______
2837 kaklik 166  
2836 kaklik 167 void sht_comreset (void)
2779 kaklik 168 {
169 int8 i;
170  
171 output_float(sht_data_pin); //data high
172 output_low(sht_clk_pin); //clk low
173 delay_us(5);
174 for(i=0; i<9; i++)
175 {
176 output_high(sht_clk_pin); //toggle clk 9 times
177 delay_us(5);
178 output_low(sht_clk_pin);
179 delay_us(5);
180 }
2836 kaklik 181 sht_comstart();
2779 kaklik 182 }
183  
184  
185 //***** Function to soft reset SHT75 *****
186  
187 void sht_soft_reset (void)
188 {
2836 kaklik 189 sht_comreset(); //SHT75 communication reset
190 sht_comwrite(0x1e); //send SHT75 reset command
2779 kaklik 191 delay_ms(15); //pause 15 ms
192 }
193  
2837 kaklik 194 //----------------------------------------------------------------------------------
195 char sht_write_statusreg(unsigned char *p_value)
196 //----------------------------------------------------------------------------------
197 // writes the status register with checksum (8-bit)
198 {
199 unsigned char error=0;
200 sht_comstart(); //transmission start
201 error+=sht_comwrite(STATUS_REG_W);//send command to sensor
202 error+=sht_comwrite(*p_value); //send value of status register
203 return error; //error>=1 in case of no response form the sensor
204 }
2779 kaklik 205  
206 //***** Function to measure SHT75 temperature *****
207  
2836 kaklik 208 int16 sht_measuretemp (void)
2779 kaklik 209 {
210 int1 ack;
211 int16 iobyte;
212  
2836 kaklik 213 sht_comstart(); //alert SHT75
214 ack = sht_comwrite(0x03); //send measure temp command and read ack status
2779 kaklik 215 if(ack == 1) return;
2836 kaklik 216 sht_comwait(); //wait for SHT75 measurement to complete
217 iobyte = sht_comread(); //read SHT75 temp data
2779 kaklik 218 return(iobyte);
219 }
220  
221  
222 //***** Function to measure SHT75 RH *****
223  
2836 kaklik 224 int16 sht_measurehumid (void)
2779 kaklik 225 {
226 int1 ack;
227 int16 iobyte;
228  
2836 kaklik 229 sht_comstart(); //alert SHT75
230 ack = sht_comwrite(0x05); //send measure RH command and read ack status
2779 kaklik 231 if(ack == 1) return;
2836 kaklik 232 sht_comwait(); //wait for SHT75 measurement to complete
233 iobyte = sht_comread(); //read SHT75 temp data
2779 kaklik 234 return(iobyte);
235 }
236  
237  
238 //***** Function to calculate SHT75 temp & RH *****
239  
240 void calculate_data (int16 temp, int16 humid, float & tc, float & rhlin, float & rhtrue)
241 {
2837 kaklik 242 const float C1=-2.0468; // for 12 Bit RH
243 const float C2=+0.0367; // for 12 Bit RH
244 const float C3=-0.0000015955; // for 12 Bit RH
245 const float T1=+0.01; // for 12 Bit RH
246 const float T2=+0.00008; // for 12 Bit RH
2836 kaklik 247 float rh;
2779 kaklik 248  
249 //calculate temperature reading
250 tc = ((float) temp * 0.01) - 40.0;
251  
252 //calculate Real RH reading
253 rh = (float) humid;
254  
2837 kaklik 255 rhlin = C1 + (rh * C2) + (rh * rh * C3);
2779 kaklik 256  
257 //calculate True RH reading
258 rhtrue = ((tc - 25.0) * (0.01 + (0.00008 * rh))) + rhlin;
2837 kaklik 259  
260 if(rhtrue>99)rhtrue=100; //cut if the value is outside of
261 if(rhtrue<0.1)rhtrue=0.1; //the physical possible range
2779 kaklik 262 }
263  
264  
265 //***** Function to measure & calculate SHT75 temp & RH *****
266  
267 void sht_rd (float & temp, float & truehumid)
268 {
269 int16 restemp, reshumid;
270 float realhumid;
271 restemp = 0; truehumid = 0;
272  
2836 kaklik 273 restemp = sht_measuretemp(); //measure temp
274 reshumid = sht_measurehumid(); //measure RH
2779 kaklik 275 calculate_data (restemp, reshumid, temp, realhumid, truehumid); //calculate temp & RH
276 }
277  
278  
279 //***** Function to initialise SHT75 on power-up *****
280  
281 void sht_init (void)
282 {
2836 kaklik 283 sht_comreset(); //reset SHT75
2779 kaklik 284 delay_ms(20); //delay for power-up
285 }
2837 kaklik 286  
287 //--------------------------------------------------------------------
288 float calc_dewpoint(float h,float t)
289 //--------------------------------------------------------------------
290 // calculates dew point
291 // input: humidity [%RH], temperature [K]
292 // output: dew point [K]
293 { float k,dew_point ;
294  
295 k = (log10(h)-2)/0.4343 + (17.62*t)/(243.12+t);
296 dew_point = 243.12*k/(17.62-k);
297 return dew_point;
298 }
299