Rev Author Line No. Line
2754 kaklik 1 ///////////////////////////////////////////////////////////////////////////////
2 // //
3 // Driver file for SHT75 Temperature & Humidity Sensor //
4 // //
5 // ***** To initialise SHT75 sensor upon power up ***** //
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_D3 //(I use A1 as data input)
19 #define sht_clk_pin PIN_C4
20  
21  
22  
23  
24 //***** Function to alert SHT75 *****
25  
26 void comstart (void)
27 {
28 output_float(sht_data_pin); //data high
29 output_bit(sht_clk_pin, 0); //clk low
30 delay_us(1);
31 output_bit(sht_clk_pin, 1); //clk high
32 delay_us(1);
33 output_bit(sht_data_pin, 0); //data low
34 delay_us(1);
35 output_bit(sht_clk_pin, 0); //clk low
36 delay_us(2);
37 output_bit(sht_clk_pin, 1); //clk high
38 delay_us(1);
39 output_float(sht_data_pin); //data high
40 delay_us(1);
41 output_bit(sht_clk_pin, 0); //clk low
42 }
43  
44  
45 //***** Function to write data to SHT75 *****
46  
47 int1 comwrite (int8 iobyte)
48 {
49 int8 i, mask = 0x80;
50 int1 ack;
51  
52 //Shift out command
53 delay_us(4);
54 for(i=0; i<8> 0) output_float(sht_data_pin); //data high if MSB high
55 else output_bit(sht_data_pin, 0); //data low if MSB low
56 delay_us(1);
57 output_bit(sht_clk_pin, 1); //clk high
58 delay_us(1);
59 mask = mask >> 1; //shift to next bit
60 }
61  
62 //Shift in ack
63 output_bit(sht_clk_pin, 0); //clk low
64 delay_us(1);
65 ack = input(sht_data_pin); //get ack bit
66 output_bit(sht_clk_pin, 1); //clk high
67 delay_us(1);
68 output_bit(sht_clk_pin, 0); //clk low
69 return(ack);
70 }
71  
72  
73 //***** Function to read data from SHT75 *****
74  
75 int16 comread (void)
76 {
77 int8 i;
78 int16 iobyte = 0;
79 const int16 mask0 = 0x0000;
80 const int16 mask1 = 0x0001;
81  
82 //shift in MSB data
83 for(i=0; i<8; i++)
84 {
85 iobyte = iobyte << 1;
86 output_bit(sht_clk_pin, 1); //clk high
87 delay_us(1);
88 if (input(sht_data_pin)) iobyte |= mask1; //shift in data bit
89 else iobyte |= mask0;
90 output_bit(sht_clk_pin, 0); //clk low
91 delay_us(1);
92 }
93  
94 //send ack 0 bit
95 output_bit(sht_data_pin, 0); //data low
96 delay_us(1);
97 output_bit(sht_clk_pin, 1); //clk high
98 delay_us(2);
99 output_bit(sht_clk_pin, 0); //clk low
100 delay_us(1);
101 output_float(sht_data_pin); //data high
102  
103 //shift in LSB data
104 for(i=0; i<8; i++)
105 {
106 iobyte = iobyte << 1;
107 output_bit(sht_clk_pin, 1); //clk high
108 delay_us(1);
109 if (input(sht_data_pin)) iobyte |= mask1; //shift in data bit
110 else iobyte |= mask0;
111 output_bit(sht_clk_pin, 0); //clk low
112 delay_us(1);
113 }
114  
115 //send ack 1 bit
116 output_float(sht_data_pin); //data high
117 delay_us(1);
118 output_bit(sht_clk_pin, 1); //clk high
119 delay_us(2);
120 output_bit(sht_clk_pin, 0); //clk low
121  
122 return(iobyte);
123 }
124  
125  
126 //***** Function to wait for SHT75 reading *****
127  
128 void comwait (void)
129 {
130 int16 sht_delay;
131  
132 output_float(sht_data_pin); //data high
133 output_bit(sht_clk_pin, 0); //clk low
134 delay_us(1);
135 for(sht_delay=0; sht_delay<30000; sht_delay++) // wait for max 300ms
136 {
137 if (!input(sht_data_pin)) break; //if sht_data_pin low, SHT75 ready
138 delay_us(10);
139 }
140 }
141  
142  
143 //***** Function to reset SHT75 communication *****
144  
145 void comreset (void)
146 {
147 int8 i;
148  
149 output_float(sht_data_pin); //data high
150 output_bit(sht_clk_pin, 0); //clk low
151 delay_us(2);
152 for(i=0; i<9; i++)
153 {
154 output_bit(sht_clk_pin, 1); //toggle clk 9 times
155 delay_us(2);
156 output_bit(sht_clk_pin, 0);
157 delay_us(2);
158 }
159 comstart();
160 }
161  
162  
163 //***** Function to soft reset SHT75 *****
164  
165 void sht_soft_reset (void)
166 {
167 comreset(); //SHT75 communication reset
168 comwrite(0x1e); //send SHT75 reset command
169 delay_ms(15); //pause 15 ms
170 }
171  
172  
173 //***** Function to measure SHT75 temperature *****
174  
175 int16 measuretemp (void)
176 {
177 int1 ack;
178 int16 iobyte;
179  
180 comstart(); //alert SHT75
181 ack = comwrite(0x03); //send measure temp command and read ack status
182 if(ack == 1) return;
183 comwait(); //wait for SHT75 measurement to complete
184 iobyte = comread(); //read SHT75 temp data
185 return(iobyte);
186 }
187  
188  
189 //***** Function to measure SHT75 RH *****
190  
191 int16 measurehumid (void)
192 {
193 int1 ack;
194 int16 iobyte;
195  
196 comstart(); //alert SHT75
197 ack = comwrite(0x05); //send measure RH command and read ack status
198 if(ack == 1) return;
199 comwait(); //wait for SHT75 measurement to complete
200 iobyte = comread(); //read SHT75 temp data
201 return(iobyte);
202 }
203  
204  
205 //***** Function to calculate SHT75 temp & RH *****
206  
207 void calculate_data (int16 temp, int16 humid, float & tc, float & rhlin, float & rhtrue)
208 {
209 float truehumid1, rh;
210  
211 //calculate temperature reading
212 tc = ((float) temp * 0.01) - 40.0;
213  
214 //calculate Real RH reading
215 rh = (float) humid;
216  
217 rhlin = (rh * 0.0405) - (rh * rh * 0.0000028) - 4.0;
218  
219 //calculate True RH reading
220 rhtrue = ((tc - 25.0) * (0.01 + (0.00008 * rh))) + rhlin;
221 }
222  
223  
224 //***** Function to measure & calculate SHT75 temp & RH *****
225  
226 void sht_rd (float & temp, float & truehumid)
227 {
228 int16 restemp, reshumid;
229 float realhumid;
230 restemp = 0; truehumid = 0;
231  
232 restemp = measuretemp(); //measure temp
233 reshumid = measurehumid(); //measure RH
234 calculate_data (restemp, reshumid, temp, realhumid, truehumid); //calculate temp & RH
235 }
236  
237  
238 //***** Function to initialise SHT75 on power-up *****
239  
240 void sht_init (void)
241 {
242 comreset(); //reset SHT75
243 delay_ms(20); //delay for power-up
244 }
245