Revision 2:340957cc8fef, committed 2011-07-09

Comitter:

hwkit

Date:

Sat Jul 09 02:18:38 2011 +0000

Parent:

1:5b20ff4fd227

Commit message:

0.1 -> Beta test

Changed in this revision

diff -r 5b20ff4fd227 -r 340957cc8fef DHT22.cpp
--- a/DHT22.cpp	Mon Jul 04 07:35:03 2011 +0000
+++ b/DHT22.cpp	Sat Jul 09 02:18:38 2011 +0000
@@ -1,6 +1,6 @@
 /*
     DHT22.cpp - DHT22 sensor library
-    Developed by Ben Adams = 2011
+    Developed by HO WING KIT
 
     This library is free software; you can redistribute it and / or
     modify it under the terms of the GNU Leser General Public
@@ -19,19 +19,11 @@
 
     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
-    Return DHT_ERROR_CHECKSUM on check sum mismatch
+    same as RHT03 http://www.humiditycn.com    
 
-    Version 0.3: 17-Jan-2011 by Ben Adams
-    This version reads data
-    Needs check sum code added at the end of readData
-
-    Version 0.2: 16-Jan-2011 by Ben Adams
-    Changed coding style to match other Arduino Libraries.
-    This version will not read data either!
-
+    Version 0.1: 8-Jan-2011 by Ho Wing Kit
+                 Beata test
+    
 */
 
 #include "DHT22.h"
@@ -39,11 +31,12 @@
 
 // This should be 40, but the sensor is adding an extra bit at the start
 #define DHT22_DATA_BIT_COUNT 41
-
+                           // debug
 Serial pc(USBTX, USBRX);   // Tx, Rx Using USB Virtual Serial Port
                            // Read Data From /etc/ttyACM* (linux port)
 
 DHT22::DHT22(PinName Data) {
+
     _data = Data;                // Set Data Pin
     _lastReadTime = time(NULL);
     _lastHumidity = 0;
@@ -59,114 +52,149 @@
     int currentHumidity=0;
     unsigned int checkSum = 0, csPart1, csPart2, csPart3, csPart4;
     unsigned int bitTimes[DHT22_DATA_BIT_COUNT];
+    
     time_t currentTime = time(NULL);
 
     DigitalInOut  DATA(_data);
-
+   
        
     for (i = 0; i < DHT22_DATA_BIT_COUNT; i++) {
         bitTimes[i] = 0;
     }
     
-    if (currentTime - _lastReadTime < 2) {
-        // Caller needs to wait 2 seconds between each call to read Data        
-        pc.printf("Current Time: %s\n",currentTime);
-        pc.printf("Last Read Time: %s\n", _lastReadTime);
+    if (int(currentTime - _lastReadTime) < 2) {        
+        pc.printf("DHT22 Error Too Quick, wiat...");
         return DHT_ERROR_TOOQUICK;
-    }
-    _lastReadTime = currentTime;
+    }   
     retryCount = 0;
     // Pin needs to start HIGH, wait unit it is HIGH with a timeout
     do {
         if (retryCount > 125) {
+            pc.printf("DHT22 Bus busy! ");
             return DHT_BUS_HUNG;
         }
         retryCount ++;
         wait_us(2);
-    } while (DATA==1);
+    } while (DATA==0);   // exit on DHT22 retrun 'High' Signal within 250us
+    
     // Send the activate pulse
+    // Step 1: MCU send out start signal to DHT22 and DHT22 send
+    //         response signal to MCU.
+    // If always signal high-voltage-level, it means DHT22 is not 
+    // working properly, plesee check the electrical connection status.
+    //
     DATA = 0;        // MCU send out start signal to DHT22
     wait_us(1100);   // 1.1 ms
+    DATA = 1;        // MCU pull up 
+    wait_us(30);     // 30 us
     // Find the start of the ACK Pulse
     retryCount = 0;
     do {
-        if (retryCount > 25)  {// (Spec is 20 to 40 us, 25*2 == 50us
+        if (retryCount > 40)  {// (Spec is 80 us, 40*2 == 80us
+            pc.printf("DHT22 is not present! ");
             return DHT_ERROR_NOT_PRESENT;
         }
         retryCount ++;
         wait_us(2);
-    } while (DATA==1);
-    // Find the end of the ACK Pulse
+    } while (DATA==1);   // Exit on DHT22 pull low within 80us
+    
+    // Find the last of the ACK Pulse
     retryCount = 0;
     do {
-        if (retryCount > 50) {// (Spec is 80 us, 50 * 2 == 100us)
+        if (retryCount > 40) {// (Spec is 80 us, 40 * 2 == 100us)
+            pc.printf("DHT22 error timeout for receiveing last ack signal! ");
             return DHT_ERROR_ACK_TOO_LONG;
         }
         retryCount++;
         wait_us(2);
-    } while (DATA==0);
-    // Read the 40 bit data stream
+    } while (DATA==0); // Exit on DHT22 pull high within 80us
+
+    // Reading the 40 bit data stream
+    // Step 2: DHT22 send data to MCU
+    //         Start bit -> low volage within 50us
+    //         0         -> high volage within 26-28 us
+    //         1         -> high volage within 70us
+    // 
+         
     for (i=0; i < DHT22_DATA_BIT_COUNT; i++) {
         retryCount = 0;
-        do {
-            if (retryCount > 35) { // spec is 50 u, 35*2 = 70 us
+        do {                       // Getting start bit signal 
+            if (retryCount > 25) { // spec is 50 u, 25*2 = 50 us
+                pc.printf("DHT22 sync timeout error! ");
                 return DHT_ERROR_SYNC_TIMEOUT;
             }
             retryCount ++;
             wait_us(2);
-        } while (DATA==1);
+        } while (DATA==0);   // Exit on high volage within 50us
         // Measure the width of the data pulse
         retryCount = 0;
         do {
-            if (retryCount > 50) { // spec is 80us, 50*2 == 100us
+            if (retryCount > 40) { // spec is 80us, 50*2 == 100us
+                pc.printf("DHT22 ERROR DATA TIMEOUT\n");
                 return DHT_ERROR_DATA_TIMEOUT;
             }
             retryCount++;
             wait_us(2);
-        } while (DATA==0);
-        bitTimes[i] = retryCount;
+        } while (DATA==1);        // Exit on low volage below 80us
+        bitTimes[i] = retryCount; // Assign bitTimes in us
     }
 
     // Now bitTimes have the number of retries (us *2)
     // that were needed to find the end of each data bit
     // Spec: 0 is 26 to 28 us
     // Spec: 1 is 70 us
-    // bitTimes[x] <= 11 is a 0
-    // bitTimes[x] > 11 is a 1
+    // bitTimes[x] <= 14 is a 0 (14x2us = 28us)
+    // bitTimes[x] > 15  is a 1 (15x2us = 30us)
     // Note: the bits are offset by one from the data sheet, not sure why
+    currentHumidity   = 0;
+    currentTemperature = 0;
+    checkSum           = 0;
+    // First 16 bit is Humidity
     for (i=0; i<16; i++) {
-        if (bitTimes[i+1] > 11) {
+        if (bitTimes[i] > 14) {
+            pc.printf("%d: bit time is %d us. ", i, bitTimes[i]);
             currentHumidity |= ( 1 << (15-i));
         }
     }
-
+    
+    // Second 16 bit is Temperature 
     for (i=0; i<16; i ++) {
-        if (bitTimes[i+17] > 11) {
+        if (bitTimes[i+16] > 14) {
             currentTemperature |= (1 <<(15-i));
         }
     }
 
+    // Last 8 bit is Checksum
     for (i=0; i<8; i++) {
-        if (bitTimes[i+33]>11) {
+        if (bitTimes[i+32] > 14) {
             checkSum |= (1 << (7-i));
         }
     }
-    _lastHumidity = (float(currentHumidity & 0x7FFF) / 10.0);
-    if (currentTemperature &= 0x8000) {
-        currentTemperature &= 0x7FFF;
-        _lastTemperature = (float(currentTemperature) / 10.0) * -1.0;
+   
+    _lastHumidity = (float(currentHumidity) / 10.0);
+    
+    // if first bit of currentTemperature is 1, it is negative value.
+    
+    if ((currentTemperature &= 0x8000)==0x8000) {        
+        _lastTemperature = (float(currentTemperature & 0x7FFF) / 10.0) * -1.0;
     } else {
         _lastTemperature = float(currentTemperature) / 10.0;
     }
 
     // Calculate Check Sum
+    //           
     csPart1 = currentHumidity >> 8;
     csPart2 = currentHumidity & 0xFF;
     csPart3 = currentTemperature >> 8;
     csPart4 = currentTemperature & 0xFF;
     if (checkSum == ((csPart1 + csPart2 + csPart3 + csPart4) & 0xFF)) {
+        pc.printf("Calculate check sum is %d.",(csPart1 + csPart2 + csPart3 + csPart4) & 0xFF);
+        pc.printf("Reading check sum is %d.",checkSum);
+        _lastReadTime = currentTime;
+        pc.printf("OK-->Temperature:%d, Humidity:%d\n", _lastTemperature, _lastHumidity);
         return DHT_ERROR_NONE;
     }
+    pc.printf("DHT22 Checksum error!");
     return DHT_ERROR_CHECKSUM;
 }