Revision 0:42ffca439fcc, committed 2012-03-29

Comitter:

crazystick

Date:

Thu Mar 29 06:14:07 2012 +0000

Commit message:

Updates from around the web, still some issues but at least it now reads reliably for me

Changed in this revision

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/DHT22.cpp	Thu Mar 29 06:14:07 2012 +0000
@@ -0,0 +1,217 @@
+/*
+    DHT22.cpp - DHT22 sensor library
+    Developed by HO WING KIT
+    Modifications by Paul Adams
+
+    This library is free software; you can redistribute it and / or
+    modify it under the terms of the GNU Leser General Public
+    License as published by the Free Software Foundation; either
+    version 2.1 of the License, or (at your option) any later version.
+
+    This library is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRENTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PATRICULAR PURPOSE.  See the GNU
+    Lesser General Public License for more details.
+
+    You should have received a copy of the GNU Lesser General Public
+    License along with this library; if not, write to the Free Software
+    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+
+
+    Humidity and Temperature Sensor DHT22 info found at
+    http://www.sparkfun.com/products/10167
+    same as RHT03 http://www.humiditycn.com    
+
+    Version 0.1: 8-Jan-2011 by Ho Wing Kit
+    Version 0.2: 29-Mar-2012 by Paul Adams
+    
+    Additional Credit: All the commenters on http://www.sparkfun.com/products/10167
+    
+*/
+
+#include "DHT22.h"
+
+// This should be 40, but the sensor is adding an extra bit at the start
+#define DHT22_DATA_BIT_COUNT 41
+
+DHT22::DHT22(PinName Data) {
+
+    _data = Data;                // Set Data Pin
+    _lastReadTime = time(NULL);
+    _lastHumidity = 0;
+    _lastTemperature = DHT22_ERROR_VALUE;
+}
+
+DHT22::~DHT22() {
+}
+
+DHT22_ERROR DHT22::readData() {
+    int i, j, retryCount;
+    int currentTemperature=0;
+    int currentHumidity=0;
+    unsigned int checkSum = 0, csPart1, csPart2, csPart3, csPart4;
+    unsigned int bitTimes[DHT22_DATA_BIT_COUNT];
+    DHT22_ERROR err = DHT_ERROR_NONE;
+    time_t currentTime = time(NULL);
+
+    DigitalInOut  DATA(_data);
+       
+    for (i = 0; i < DHT22_DATA_BIT_COUNT; i++) {
+        bitTimes[i] = 0;
+    }
+    
+    if (int(currentTime - _lastReadTime) < 2) {        
+        printf("DHT22 Error Access Time < 2s");
+        err = DHT_ERROR_TOO_QUICK;
+    }   
+    retryCount = 0;
+    // Pin needs to start HIGH, wait unit it is HIGH with a timeout
+    do {
+        if (retryCount > 125) {
+            printf("DHT22 Bus busy!");
+            err = DHT_BUS_HUNG;
+        }
+        retryCount ++;
+        wait_us(2);
+    } while (DATA==0);   // exit on DHT22 return '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, please check the electrical connection status.
+    //
+    DATA.output(); // set pin to output data
+    DATA = 0;      // MCU send out start signal to DHT22
+    wait_ms(18);   // 18 ms wait (spec: at least 1ms)
+    DATA = 1;      // MCU pull up 
+    wait_us(40);
+    DATA.input();  // set pin to receive data
+    // Find the start of the ACK Pulse
+    retryCount = 0;
+    do {
+        if (retryCount > 40)  { // (Spec is 20-40 us high)
+            printf("DHT22 not responding!");
+            err = DHT_ERROR_NOT_PRESENT;
+        }
+        retryCount++;
+        wait_us(1);
+    } while (DATA==1);   // Exit on DHT22 pull low within 40us
+    if (err != DHT_ERROR_NONE) {
+        // initialisation failed
+        return err;    
+    }
+    wait_us(80); // DHT pull up ready to transmit data
+    
+    /*
+    if (DATA == 0) {
+        printf("DHT22 not ready!");
+        err = DHT_ERROR_ACK_TOO_LONG;
+        return err;
+    }
+    */
+    
+    // Reading the 5 byte data stream
+    // Step 2: DHT22 send data to MCU
+    //         Start bit -> low volage within 50us (actually could be anything from 35-75us)
+    //         0         -> high volage within 26-28us (actually could be 10-40us)
+    //         1         -> high volage within 70us (actually could be 60-85us)
+    //         See http://www.sparkfun.com/products/10167#comment-4f118d6e757b7f536e000000
+    
+    
+    for (i = 0; i < 5; i++) {
+        for (j = 0; j < 8; j++) {
+            // Instead of relying on the data sheet, just wait while the RHT03 pin is low
+            retryCount = 0;
+            do {
+                if (retryCount > 75)  {
+                    printf("DHT22 timeout waiting for data!");
+                    err = DHT_ERROR_DATA_TIMEOUT;
+                }
+                retryCount++;
+                wait_us(1);
+            } while (DATA == 0);
+            // We now wait for 40us
+            wait_us(40);
+            if (DATA == 1) {  
+                // If pin is still high, bit value is a 1
+                bitTimes[i*8+j] = 1;
+            } else {  
+                // The bit value is a 0
+                bitTimes[i*8+j] = 0;
+            }
+            int count = 0;
+            while (DATA == 1 && count < 100) {  
+                wait_us(1); // Delay for 1 microsecond  
+                count++;  
+            }
+        }
+    }
+    // Re-init DHT22 pin  
+    DATA.output();  
+    DATA = 1;
+
+    // Now bitTimes have the actual bits
+    // that were needed to find the end of each data bit
+    // Note: the bits are offset by one from the data sheet, not sure why
+    currentHumidity    = 0;
+    currentTemperature = 0;
+    checkSum           = 0;
+    // First 16 bits is Humidity
+    for (i=0; i<16; i++) {
+        //printf("bit %d: %d  ", i, bitTimes[i+1]);
+        if (bitTimes[i+1] > 0) {
+            currentHumidity |= ( 1 << (15-i));
+        }
+    }
+    
+    // Second 16 bits is Temperature 
+    for (i=0; i<16; i ++) {
+        //printf("bit %d: %d  ", i+16, bitTimes[i+17]);
+        if (bitTimes[i+17] > 0) {
+            currentTemperature |= (1 <<(15-i));
+        }
+    }
+
+    // Last 8 bit is Checksum
+    for (i=0; i<8; i++) {
+        //printf("bit %d: %d  ", i+32, bitTimes[i+33]);
+        if (bitTimes[i+33] > 0) {
+            checkSum |= (1 << (7-i));
+        }
+    }
+   
+    _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)) {
+        _lastReadTime = currentTime;
+        printf("OK-->Temperature:%f, Humidity:%f\r\n", _lastTemperature, _lastHumidity);
+        err = DHT_ERROR_NONE;
+    } else {
+        printf("DHT22 Checksum error!\n");
+        printf("Calculate check sum is %d\n",(csPart1 + csPart2 + csPart3 + csPart4) & 0xFF);
+        printf("Reading check sum is %d",checkSum);
+        err = DHT_ERROR_CHECKSUM;
+    }
+    return err;
+}
+
+float DHT22::getTemperatureC() {
+    return _lastTemperature;
+}
+
+float DHT22::getHumidity() {
+    return _lastHumidity;
+}
\ No newline at end of file

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/DHT22.h	Thu Mar 29 06:14:07 2012 +0000
@@ -0,0 +1,84 @@
+/* mbed DHT22 Library
+ * Copyright (c) 2011, sford, http://mbed.org
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documnetation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to  whom the Software is
+ * furished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS OR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#ifndef MBED_DHT22_H
+#define MBED_DHT22_H
+
+#include "mbed.h"
+
+/**
+ * Currently supports DHT22 (SparkFun Electronics)
+ * Humidity and Temperature Sensor
+ *
+ * Features:
+ *  >   3.3-6V Input
+ *  >   1-1.5mA measuring current
+ *  >   40-50uA standby current
+ *  >   Humidity from 0-100% RH
+ *  >   -40 - 80 degrees C  temperature range
+ *  >   +-2% RH accuracy
+ *  >   +-0.5 degrees C
+ *
+ * Usages
+ * #include "DHT22.h"
+ *
+ * DTH22 dth22(PinName sda, PinName scl, int addr);  // pin
+ *
+ * int main() {
+ *     err=dth22.readData();
+ *     if (err==0) {
+          printf("Temperature is %f.2 C\n",dht22.getTemperature());
+          printf("Humidity is %f.2 \%\n",dht22.getHumidity());
+       }
+ *
+ *
+ */
+
+#define DHT22_ERROR_VALUE -99.5
+
+typedef enum {
+    DHT_ERROR_NONE = 0,
+    DHT_BUS_HUNG,
+    DHT_ERROR_NOT_PRESENT,
+    DHT_ERROR_ACK_TOO_LONG,
+    DHT_ERROR_SYNC_TIMEOUT,
+    DHT_ERROR_DATA_TIMEOUT,
+    DHT_ERROR_CHECKSUM,
+    DHT_ERROR_TOO_QUICK
+} DHT22_ERROR;
+
+class DHT22 {
+private:
+    time_t  _lastReadTime;
+    PinName _data;
+    float   _lastHumidity;
+    float   _lastTemperature;
+public:
+    DHT22(PinName Data);
+    ~DHT22();
+    DHT22_ERROR readData(void);
+    float getHumidity();
+    float getTemperatureC();
+    void clockReset();
+};
+
+#endif /*_DHT22_H_*/