Rev 2766 Rev 2779
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1 /////////////////////////////////////////////////////////////////////////////// 1 ///////////////////////////////////////////////////////////////////////////////
2 // // 2 // //
3 // Driver file for SHT75 Temperature & Humidity Sensor // 3 // Driver file for SHT75 Temperature & Humidity Sensor //
4 // // 4 // //
5 // ***** To initialise SHT75 sensor upon power up ***** // 5 // ***** To initialise SHT75 sensor upon power up ***** //
6 // // 6 // //
7 // Function : sht_init() // 7 // Function : sht_init() //
8 // Return : none // 8 // Return : none //
9 // // 9 // //
10 // // 10 // //
11 // ***** To measure and caluculate SHT75 temp & real RH ***** // 11 // ***** To measure and caluculate SHT75 temp & real RH ***** //
12 // // 12 // //
13 // Function : sht_rd (temp, truehumid) // 13 // Function : sht_rd (temp, truehumid) //
14 // Return : temperature & true humidity in float values // 14 // Return : temperature & true humidity in float values //
15 // // 15 // //
16 /////////////////////////////////////////////////////////////////////////////// 16 ///////////////////////////////////////////////////////////////////////////////
17   17  
18 #define sht_data_pin PIN_D0 18 //#define sht_data_pin PIN_D0
19 #define sht_clk_pin PIN_D1 19 //#define sht_clk_pin PIN_D1
20   20  
21   21  
22 //***** Function to alert SHT75 ***** 22 //***** Function to alert SHT75 *****
23   23  
24 void comstart (void) 24 void comstart (void)
25 { 25 {
26 output_float(sht_data_pin); //data high 26 output_float(sht_data_pin); //data high
27 output_low(sht_clk_pin); //clk low 27 output_low(sht_clk_pin); //clk low
28 delay_us(2); 28 delay_us(2);
29 output_high(sht_clk_pin); //clk high 29 output_high(sht_clk_pin); //clk high
30 delay_us(2); 30 delay_us(2);
31 output_low(sht_data_pin); //data low 31 output_low(sht_data_pin); //data low
32 delay_us(2); 32 delay_us(2);
33 output_low(sht_clk_pin); //clk low 33 output_low(sht_clk_pin); //clk low
34 delay_us(5); 34 delay_us(5);
35 output_high(sht_clk_pin); //clk high 35 output_high(sht_clk_pin); //clk high
36 delay_us(2); 36 delay_us(2);
37 output_float(sht_data_pin); //data high 37 output_float(sht_data_pin); //data high
38 delay_us(2); 38 delay_us(2);
39 output_low(sht_clk_pin); //clk low 39 output_low(sht_clk_pin); //clk low
40 } 40 }
41   41  
42   42  
43 //***** Function to write data to SHT75 ***** 43 //***** Function to write data to SHT75 *****
44   44  
45 int1 comwrite (int8 iobyte) 45 int1 comwrite (int8 iobyte)
46 { 46 {
47 int8 i, mask = 0x80; 47 int8 i, mask = 0x80;
48 int1 ack; 48 int1 ack;
49   49  
50 //Shift out command 50 //Shift out command
51 delay_us(5); 51 delay_us(5);
52 for(i=0; i<8; i++) 52 for(i=0; i<8; i++)
53 { 53 {
54 output_low(sht_clk_pin); //clk low 54 output_low(sht_clk_pin); //clk low
55 if((iobyte & mask) > 0) output_float(sht_data_pin); //data high if MSB high 55 if((iobyte & mask) > 0) output_float(sht_data_pin); //data high if MSB high
56 else output_low(sht_data_pin); //data low if MSB low 56 else output_low(sht_data_pin); //data low if MSB low
57 delay_us(2); 57 delay_us(2);
58 output_high(sht_clk_pin); //clk high 58 output_high(sht_clk_pin); //clk high
59 delay_us(2); 59 delay_us(2);
60 mask = mask >> 1; //shift to next bit 60 mask = mask >> 1; //shift to next bit
61 } 61 }
62   62  
63 //Shift in ack 63 //Shift in ack
64 output_low(sht_clk_pin); //clk low 64 output_low(sht_clk_pin); //clk low
65 delay_us(2); 65 delay_us(2);
66 ack = input(sht_data_pin); //get ack bit 66 ack = input(sht_data_pin); //get ack bit
67 output_high(sht_clk_pin); //clk high 67 output_high(sht_clk_pin); //clk high
68 delay_us(2); 68 delay_us(2);
69 output_low(sht_clk_pin); //clk low 69 output_low(sht_clk_pin); //clk low
70 return(ack); 70 return(ack);
71 } 71 }
72   72  
73   73  
74 //***** Function to read data from SHT75 ***** 74 //***** Function to read data from SHT75 *****
75   75  
76 int16 comread (void) 76 int16 comread (void)
77 { 77 {
78 int8 i; 78 int8 i;
79 int16 iobyte = 0; 79 int16 iobyte = 0;
80 const int16 mask0 = 0x0000; 80 const int16 mask0 = 0x0000;
81 const int16 mask1 = 0x0001; 81 const int16 mask1 = 0x0001;
82   82  
83 //shift in MSB data 83 //shift in MSB data
84 for(i=0; i<8; i++) 84 for(i=0; i<8; i++)
85 { 85 {
86 iobyte = iobyte << 1; 86 iobyte = iobyte << 1;
87 output_high(sht_clk_pin); //clk high 87 output_high(sht_clk_pin); //clk high
88 delay_us(2); 88 delay_us(2);
89 if (input(sht_data_pin)) iobyte |= mask1; //shift in data bit 89 if (input(sht_data_pin)) iobyte |= mask1; //shift in data bit
90 else iobyte |= mask0; 90 else iobyte |= mask0;
91 output_low(sht_clk_pin); //clk low 91 output_low(sht_clk_pin); //clk low
92 delay_us(2); 92 delay_us(2);
93 } 93 }
94   94  
95 //send ack 0 bit 95 //send ack 0 bit
96 output_low(sht_data_pin); //data low 96 output_low(sht_data_pin); //data low
97 delay_us(2); 97 delay_us(2);
98 output_high(sht_clk_pin); //clk high 98 output_high(sht_clk_pin); //clk high
99 delay_us(5); 99 delay_us(5);
100 output_low(sht_clk_pin); //clk low 100 output_low(sht_clk_pin); //clk low
101 delay_us(2); 101 delay_us(2);
102 output_float(sht_data_pin); //data high 102 output_float(sht_data_pin); //data high
103   103  
104 //shift in LSB data 104 //shift in LSB data
105 for(i=0; i<8; i++) 105 for(i=0; i<8; i++)
106 { 106 {
107 iobyte = iobyte << 1; 107 iobyte = iobyte << 1;
108 output_high(sht_clk_pin); //clk high 108 output_high(sht_clk_pin); //clk high
109 delay_us(2); 109 delay_us(2);
110 if (input(sht_data_pin)) iobyte |= mask1; //shift in data bit 110 if (input(sht_data_pin)) iobyte |= mask1; //shift in data bit
111 else iobyte |= mask0; 111 else iobyte |= mask0;
112 output_low(sht_clk_pin); //clk low 112 output_low(sht_clk_pin); //clk low
113 delay_us(2); 113 delay_us(2);
114 } 114 }
115   115  
116 //send ack 1 bit 116 //send ack 1 bit
117 output_float(sht_data_pin); //data high 117 output_float(sht_data_pin); //data high
118 delay_us(2); 118 delay_us(2);
119 output_high(sht_clk_pin); //clk high 119 output_high(sht_clk_pin); //clk high
120 delay_us(5); 120 delay_us(5);
121 output_low(sht_clk_pin); //clk low 121 output_low(sht_clk_pin); //clk low
122   122  
123 return(iobyte); 123 return(iobyte);
124 } 124 }
125   125  
126   126  
127 //***** Function to wait for SHT75 reading ***** 127 //***** Function to wait for SHT75 reading *****
128   128  
129 void comwait (void) 129 void comwait (void)
130 { 130 {
131 int16 sht_delay; 131 int16 sht_delay;
132   132  
133 output_float(sht_data_pin); //data high 133 output_float(sht_data_pin); //data high
134 output_low(sht_clk_pin); //clk low 134 output_low(sht_clk_pin); //clk low
135 delay_us(2); 135 delay_us(2);
136 for(sht_delay=0; sht_delay<30000; sht_delay++) // wait for max 300ms 136 for(sht_delay=0; sht_delay<30000; sht_delay++) // wait for max 300ms
137 { 137 {
138 if (!input(sht_data_pin)) break; //if sht_data_pin low, SHT75 ready 138 if (!input(sht_data_pin)) break; //if sht_data_pin low, SHT75 ready
139 delay_us(10); 139 delay_us(10);
140 } 140 }
141 } 141 }
142   142  
143   143  
144 //***** Function to reset SHT75 communication ***** 144 //***** Function to reset SHT75 communication *****
145   145  
146 void comreset (void) 146 void comreset (void)
147 { 147 {
148 int8 i; 148 int8 i;
149   149  
150 output_float(sht_data_pin); //data high 150 output_float(sht_data_pin); //data high
151 output_low(sht_clk_pin); //clk low 151 output_low(sht_clk_pin); //clk low
152 delay_us(5); 152 delay_us(5);
153 for(i=0; i<9; i++) 153 for(i=0; i<9; i++)
154 { 154 {
155 output_high(sht_clk_pin); //toggle clk 9 times 155 output_high(sht_clk_pin); //toggle clk 9 times
156 delay_us(5); 156 delay_us(5);
157 output_low(sht_clk_pin); 157 output_low(sht_clk_pin);
158 delay_us(5); 158 delay_us(5);
159 } 159 }
160 comstart(); 160 comstart();
161 } 161 }
162   162  
163   163  
164 //***** Function to soft reset SHT75 ***** 164 //***** Function to soft reset SHT75 *****
165   165  
166 void sht_soft_reset (void) 166 void sht_soft_reset (void)
167 { 167 {
168 comreset(); //SHT75 communication reset 168 comreset(); //SHT75 communication reset
169 comwrite(0x1e); //send SHT75 reset command 169 comwrite(0x1e); //send SHT75 reset command
170 delay_ms(15); //pause 15 ms 170 delay_ms(15); //pause 15 ms
171 } 171 }
172   172  
173   173  
174 //***** Function to measure SHT75 temperature ***** 174 //***** Function to measure SHT75 temperature *****
175   175  
176 int16 measuretemp (void) 176 int16 measuretemp (void)
177 { 177 {
178 int1 ack; 178 int1 ack;
179 int16 iobyte; 179 int16 iobyte;
180   180  
181 comstart(); //alert SHT75 181 comstart(); //alert SHT75
182 ack = comwrite(0x03); //send measure temp command and read ack status 182 ack = comwrite(0x03); //send measure temp command and read ack status
183 if(ack == 1) return; 183 if(ack == 1) return;
184 comwait(); //wait for SHT75 measurement to complete 184 comwait(); //wait for SHT75 measurement to complete
185 iobyte = comread(); //read SHT75 temp data 185 iobyte = comread(); //read SHT75 temp data
186 return(iobyte); 186 return(iobyte);
187 } 187 }
188   188  
189   189  
190 //***** Function to measure SHT75 RH ***** 190 //***** Function to measure SHT75 RH *****
191   191  
192 int16 measurehumid (void) 192 int16 measurehumid (void)
193 { 193 {
194 int1 ack; 194 int1 ack;
195 int16 iobyte; 195 int16 iobyte;
196   196  
197 comstart(); //alert SHT75 197 comstart(); //alert SHT75
198 ack = comwrite(0x05); //send measure RH command and read ack status 198 ack = comwrite(0x05); //send measure RH command and read ack status
199 if(ack == 1) return; 199 if(ack == 1) return;
200 comwait(); //wait for SHT75 measurement to complete 200 comwait(); //wait for SHT75 measurement to complete
201 iobyte = comread(); //read SHT75 temp data 201 iobyte = comread(); //read SHT75 temp data
202 return(iobyte); 202 return(iobyte);
203 } 203 }
204   204  
205   205  
206 //***** Function to calculate SHT75 temp & RH ***** 206 //***** Function to calculate SHT75 temp & RH *****
207   207  
208 void calculate_data (int16 temp, int16 humid, float & tc, float & rhlin, float & rhtrue) 208 void calculate_data (int16 temp, int16 humid, float & tc, float & rhlin, float & rhtrue)
209 { 209 {
210 float truehumid1, rh; 210 float truehumid1, rh;
211   211  
212 //calculate temperature reading 212 //calculate temperature reading
213 tc = ((float) temp * 0.01) - 40.0; 213 tc = ((float) temp * 0.01) - 40.0;
214   214  
215 //calculate Real RH reading 215 //calculate Real RH reading
216 rh = (float) humid; 216 rh = (float) humid;
217   217  
218 rhlin = (rh * 0.0405) - (rh * rh * 0.0000028) - 4.0; 218 rhlin = (rh * 0.0405) - (rh * rh * 0.0000028) - 4.0;
219   219  
220 //calculate True RH reading 220 //calculate True RH reading
221 rhtrue = ((tc - 25.0) * (0.01 + (0.00008 * rh))) + rhlin; 221 rhtrue = ((tc - 25.0) * (0.01 + (0.00008 * rh))) + rhlin;
222 } 222 }
223   223  
224   224  
225 //***** Function to measure & calculate SHT75 temp & RH ***** 225 //***** Function to measure & calculate SHT75 temp & RH *****
226   226  
227 void sht_rd (float & temp, float & truehumid) 227 void sht_rd (float & temp, float & truehumid)
228 { 228 {
229 int16 restemp, reshumid; 229 int16 restemp, reshumid;
230 float realhumid; 230 float realhumid;
231 restemp = 0; truehumid = 0; 231 restemp = 0; truehumid = 0;
232   232  
233 restemp = measuretemp(); //measure temp 233 restemp = measuretemp(); //measure temp
234 reshumid = measurehumid(); //measure RH 234 reshumid = measurehumid(); //measure RH
235 calculate_data (restemp, reshumid, temp, realhumid, truehumid); //calculate temp & RH 235 calculate_data (restemp, reshumid, temp, realhumid, truehumid); //calculate temp & RH
236 } 236 }
237   237  
238   238  
239 //***** Function to initialise SHT75 on power-up ***** 239 //***** Function to initialise SHT75 on power-up *****
240   240  
241 void sht_init (void) 241 void sht_init (void)
242 { 242 {
243 comreset(); //reset SHT75 243 comreset(); //reset SHT75
244 delay_ms(20); //delay for power-up 244 delay_ms(20); //delay for power-up
245 } 245 }