| 175 | */ |
| 176 | |
| 177 | int readRHT03 (const int pin, int *temp, int *rh) |
| 178 | { |
| 179 | static struct timeval then ; // will initialise to zero |
| 180 | static int lastTemp = 0 ; |
| 181 | static int lastRh = 0 ; |
| 182 | |
| 183 | int result ; |
| 184 | struct timeval now, timeOut ; |
| 185 | unsigned char buffer [4] ; |
| 186 | |
| 187 | // The data sheets say to not read more than once every 2 seconds, so you |
| 188 | // get the last good reading |
| 189 | |
| 190 | gettimeofday (&now, NULL) ; |
| 191 | if (timercmp (&now, &then, <)) |
| 192 | { |
| 193 | *rh = lastRh ; |
| 194 | *temp = lastTemp ; |
| 195 | return true ; |
| 196 | } |
| 197 | |
| 198 | // Set timeout for next read |
| 199 | |
| 200 | gettimeofday (&now, NULL) ; |
| 201 | timerclear (&timeOut) ; |
| 202 | timeOut.tv_sec = 2 ; |
| 203 | timeradd (&now, &timeOut, &then) ; |
| 204 | |
| 205 | // Read ... |
| 206 | |
| 207 | result = maxDetectRead (pin, buffer) ; |
| 208 | |
| 209 | if (!result) // Try again, but just once |
| 210 | result = maxDetectRead (pin, buffer) ; |
| 211 | |
| 212 | if (!result) |
| 213 | return false ; |
| 214 | |
| 215 | *rh = (buffer [0] * 256 + buffer [1]) ; |
| 216 | *temp = (buffer [2] * 256 + buffer [3]) ; |
| 217 | |
| 218 | if ((*temp & 0x8000) != 0) // Negative |
| 219 | { |
| 220 | *temp &= 0x7FFF ; |
| 221 | *temp = -*temp ; |
| 222 | } |
| 223 | |
| 224 | // Discard obviously bogus readings - the checksum can't detect a 2-bit error |
| 225 | // (which does seem to happen - no realtime here) |
| 226 | |
| 227 | if ((*rh > 999) || (*temp > 800) || (*temp < -400)) |
| 228 | return false ; |
| 229 | |
| 230 | lastRh = *rh ; |
| 231 | lastTemp = *temp ; |
| 232 | |
| 233 | return true ; |
| 234 | } |