Version 0.4

Author: nethoncho

DHT22.cpp

@@ -20,6 +20,10 @@
 Humidity and Temperature Sensor DHT22 info found at
 http://www.sparkfun.com/products/10167
 
+Version 0.4: 24-Jan-2011 by Ben Adams
+Added return code constants to keywords.txt
+Returns DHT_ERROR_CHECKSUM on check sum mismatch 
+
 Version 0.3: 17-Jan-2011 by Ben Adams
 This version reads data
 Needs check sum code added at the end of readData
@@ -76,7 +80,7 @@ DHT22_ERROR_t DHT22::readData()
   uint8_t bitTimes[DHT22_DATA_BIT_COUNT];
   int currentHumidity;
   int currentTemperature;
-  uint8_t checkSum;
+  uint8_t checkSum, csPart1, csPart2, csPart3, csPart4;
   unsigned long currentTime;
   int i;
 
@@ -209,9 +213,15 @@ DHT22_ERROR_t DHT22::readData()
     _lastTemperature = float(currentTemperature) / 10.0;
   }
 
-  // TODO: Test the checksum and return DHT_ERROR_CHECKSUM if bad
-
-  return DHT_ERROR_NONE;
+  csPart1 = currentHumidity >> 8;
+  csPart2 = currentHumidity & 0xFF;
+  csPart3 = currentTemperature >> 8;
+  csPart4 = currentTemperature & 0xFF;
+  if(checkSum == ((csPart1 + csPart2 + csPart3 + csPart4) & 0xFF))
+  {
+    return DHT_ERROR_NONE;
+  }
+  return DHT_ERROR_CHECKSUM;
 }
 
 float DHT22::getHumidity()

README

@@ -4,6 +4,10 @@
 Humidity and Temperature Sensor DHT22 info found at
 http://www.sparkfun.com/products/10167
 
+Version 0.4: 24-Jan-2011 by Ben Adams
+Added return code constants to keywords.txt
+Returns DHT_ERROR_CHECKSUM on check sum mismatch 
+
 Version 0.3: 17-Jan-2011 by Ben Adams
 This version reads data
 Needs check sum code added at the end of readData

examples/Serial/Serial.pde

@@ -21,18 +21,39 @@ void loop(void)
   delay(2000);
   Serial.print("Requesting data...");
   errorCode = myDHT22.readData();
-  if(errorCode == DHT_ERROR_NONE)
+  switch(errorCode)
   {
-    Serial.print("Got Data ");
-    Serial.print(myDHT22.getTemperatureC());
-    Serial.print("C ");
-    Serial.print(myDHT22.getHumidity());
-    Serial.println("%");
-  }
-  else
-  {
-    Serial.print("Error Code ");
-    Serial.print(errorCode);
-    Serial.println(" readData Failed");
+    case DHT_ERROR_NONE:
+      Serial.print("Got Data ");
+      Serial.print(myDHT22.getTemperatureC());
+      Serial.print("C ");
+      Serial.print(myDHT22.getHumidity());
+      Serial.println("%");
+      break;
+    case DHT_ERROR_CHECKSUM:
+      Serial.print("check sum error ");
+      Serial.print(myDHT22.getTemperatureC());
+      Serial.print("C ");
+      Serial.print(myDHT22.getHumidity());
+      Serial.println("%");
+      break;
+    case DHT_BUS_HUNG:
+      Serial.println("BUS Hung ");
+      break;
+    case DHT_ERROR_NOT_PRESENT:
+      Serial.println("Not Present ");
+      break;
+    case DHT_ERROR_ACK_TOO_LONG:
+      Serial.println("ACK time out ");
+      break;
+    case DHT_ERROR_SYNC_TIMEOUT:
+      Serial.println("Sync Timeout ");
+      break;
+    case DHT_ERROR_DATA_TIMEOUT:
+      Serial.println("Data Timeout ");
+      break;
+    case DHT_ERROR_TOOQUICK:
+      Serial.println("Polled to quick ");
+      break;
   }
 }

keywords.txt

@@ -25,3 +25,12 @@ clockReset	KEYWORD2
 #######################################
 # Constants (LITERAL1)
 #######################################
+
+DHT_ERROR_NONE	LITERAL1
+DHT_BUS_HUNG	LITERAL1
+DHT_ERROR_NOT_PRESENT	LITERAL1
+DHT_ERROR_ACK_TOO_LONG	LITERAL1
+DHT_ERROR_SYNC_TIMEOUT	LITERAL1
+DHT_ERROR_DATA_TIMEOUT	LITERAL1
+DHT_ERROR_CHECKSUM	LITERAL1
+DHT_ERROR_TOOQUICK	LITERAL1