SI7021: temperature can be negative, clip at reasonable vlaues

Author: phkehl

examples/ex14/ex14.c

@@ -67,12 +67,12 @@ static void sAppTask(void *pArg)
     {
         sAppCnt++;
 
-        const uint16_t hum1  = si7021MeasHumidity();
-        const uint16_t temp1 = si7021MeasTemperature();
-        uint16_t hum2, temp2;
+        const int16_t hum1  = si7021MeasHumidity();
+        const int16_t temp1 = si7021MeasTemperature();
+        int16_t hum2, temp2;
         si7021MeasHumidityAndTemperature(&hum2, &temp2);
 
-        DEBUG("RH=%.2f (%.2f), T=%.2f (%.2f)",
+        DEBUG("H=%.2f (%.2f), T=%.2f (%.2f)",
             (float)hum1 * 0.01f, (float)hum2 * 0.01f,
             (float)temp1 * 0.01f, (float)temp2 * 0.01f);
 

src/si7021.c

@@ -125,7 +125,7 @@ void si7021Init(void)
         sn1, sn2, fw >> 4, fw & 0x0f);
 }
 
-uint16_t si7021MeasHumidity(void)
+int16_t si7021MeasHumidity(void)
 {
     if (!sSi7021Ready)
     {
@@ -146,12 +146,12 @@ uint16_t si7021MeasHumidity(void)
     }
 
     const uint16_t raw = ((uint16_t)resp[0] << 8) | resp[1];
-    const uint16_t hum = (((uint32_t)raw * (125 * 100)) / 65536) - 600;
+    const int16_t hum = (((int32_t)raw * (125 * 100)) / 65536) - 600;
 
     return CLIP(hum, 0, 10000);
 }
 
-uint16_t si7021MeasTemperature(void)
+int16_t si7021MeasTemperature(void)
 {
     if (!sSi7021Ready)
     {
@@ -172,14 +172,14 @@ uint16_t si7021MeasTemperature(void)
     }
 
     const uint16_t raw = ((uint16_t)resp[0] << 8) | resp[1];
-    const uint16_t temp = (((uint32_t)raw * (uint32_t)(175.72 * 100)) / 65536) - (uint32_t)(46.85 * 100);
+    const int16_t temp = (((int32_t)raw * (int32_t)(175.72 * 100)) / 65536) - (int32_t)(46.85 * 100);
 
-    return temp;
+    return CLIP(temp, -4600, 12800);
 }
 
 
 
-bool si7021MeasHumidityAndTemperature(uint16_t *pHum, uint16_t *pTemp)
+bool si7021MeasHumidityAndTemperature(int16_t *pHum, int16_t *pTemp)
 {
     if (!sSi7021Ready)
     {

src/si7021.h

@@ -32,19 +32,19 @@
 void si7021Init(void);
 
 //! temperature or humidity value to indicate no data available
-#define SI7021_NODATA 0xffff
+#define SI7021_NODATA 0x7fff /* = 32767 = INT16_MAX */
 
 //! measure relative humidity
 /*!
-    \returns the relative humidity value [0.01%], or #SI7021_NODATA on error
+    \returns the relative humidity value [0.01%], value 0..10000 or #SI7021_NODATA on error
 */
-uint16_t si7021MeasHumidity(void);
+int16_t si7021MeasHumidity(void);
 
 //! measure temperature
 /*!
-    \returns the temperature value [0.01C], or #SI7021_NODATA on error
+    \returns the temperature value [0.01C], value -4600..12800 or #SI7021_NODATA on error
 */
-uint16_t si7021MeasTemperature(void);
+int16_t si7021MeasTemperature(void);
 
 
 //! measure relative humidity and temperature at the same time
@@ -53,7 +53,7 @@ uint16_t si7021MeasTemperature(void);
     \param[out] pTemp  the temperature value [0.01C], or #SI7021_NODATA on error
     \returns true if both measurements are available
 */
-bool si7021MeasHumidityAndTemperature(uint16_t *pHum, uint16_t *pTemp);
+bool si7021MeasHumidityAndTemperature(int16_t *pHum, int16_t *pTemp);
 
 
 #endif // __SI7021_H__