Revision 9:056d1e9b428c, committed 2014-09-11

Comitter:

s_inoue_mbed

Date:

Thu Sep 11 13:45:00 2014 +0000

Parent:

8:160047ca45bf

Child:

10:f0d789f49df7

Commit message:

Bug fix

Changed in this revision

--- a/DHT11.cpp	Wed Sep 10 18:00:31 2014 +0000
+++ b/DHT11.cpp	Thu Sep 11 13:45:00 2014 +0000
@@ -11,72 +11,77 @@
     io_irq.rise(this, &DHT11::pos_edge);
     io_irq.fall(this, &DHT11::neg_edge);
     io_irq.disable_irq();
-    init();    
+    t.start();
     first_time = true;
 }
 
 // Destructor
 DHT11::~DHT11(void) {}
 
+// Constants
+const int DHT11::t_tol_start = 2;
+const int DHT11::t_tol_pulse = 10;
+
 // Reading the data bits from the DHT11
-int DHT11::readData()
+int DHT11::readData(void)
 {
+    // Checking the measurement frequency
+    if (t.read_ms() < 2000 && first_time == false) {
+        t.reset();
+        return READ_TOO_OFTEN;
+    }
+    
     // Initialize
     init();
 
-    // Checking the measurement frequency
-    if (t.read_ms() < 2000 & first_time == false) {
-        t.reset();
-        return TOO_FAST_READ;
-    }
-
     // Checking the data bus
     if (io == 0) {
-        io.input();
+        t.reset();
         return BUS_BUSY;
     }
 
-    // Sending start signal, low signal for 20 ms
-    io.output();
+    // Sending start signal, low signal for around 10 ms
     t.reset();
-    t.start();
     do {
         io = 0;
-    } while (t.read_ms() < 20);
+    } while (t.read_ms() < 20 + t_tol_start);
     io = 1;
-    io.input();
 
     // Waiting for the start of the response signal
     t.reset();
-    t.start();
     do {
         if (t.read_us() > 100) {
-            io.input();
+            t.reset();
             return NOT_PRESENT;
         }
     } while (io == 1);
 
     // Wainting for the start of the ready signal
     t.reset();
-    t.start();
     do {
         if (t.read_us() > 100) {
-            io.input();
+            t.reset();
             return NOT_READY;
         }
     } while (io == 0);
 
     // Wainting for the end of the ready signal
     t.reset();
-    t.start();
-    do {} while (io == 1);
+    do {
+        if (t.read_us() > 100) {
+            t.reset();
+            return WATCHDOG_ERR;
+        }
+    } while (io == 1);
 
     // Starting the pulse width sensing
+    // by the use of interruptions
     io_irq.enable_irq();
 
     do {
         wait_us(100);
         if (wdt > 50) {
+            t.reset();
             return WATCHDOG_ERR;
         }
         wdt++;
@@ -87,7 +92,9 @@
              + ((data & 0x00ff000000) >> 24)
              + ((data & 0x0000ff0000) >> 16)
              + ((data & 0x000000ff00) >> 8);
+
     if (chksum != (data & 0x00000000ff)) {
+        t.reset();
         return CHKSUM_ERR;
     } else {
         t.reset();
@@ -97,23 +104,15 @@
 }
 
 // Extracting humidity data from the received data
-int DHT11::readHumidity()
+int DHT11::readHumidity(void)
 {
-    if (err == OK) {
-        return (data & 0xff00000000) >> 32;
-    } else {
-        return 0xffffffff;
-    }
+    return (data & 0xff00000000) >> 32;
 }
 
 // Extracting temperature data from the received data
-int DHT11::readTemperature()
+int DHT11::readTemperature(void)
 {
-    if (err == OK) {
-        return (data & 0x0000ff0000) >> 16;
-    } else {
-        return 0xffffffff;
-    }
+    return (data & 0x0000ff0000) >> 16;
 }
 
 // Initialization of variables
@@ -124,8 +123,8 @@
     chksum = 0;
     cnt = 0;
     wdt = 0;
-    err = OK;
     eod = false;
+    t.reset();
 }
 
 void DHT11::pos_edge(void)
@@ -148,8 +147,8 @@
     // Reading the positive pulse width
     t_pulse_us = t.read_us();
 
-    // Detecting 0 if the pulse width ranges from 20 us to 30 us
-    if (20 <= t_pulse_us && t_pulse_us <= 30) {
+    // Detecting 0 if the pulse width ranges around 25 us
+    if (25 - t_tol_pulse <= t_pulse_us && t_pulse_us <= 30 + t_tol_pulse) {
         // Shifting the data buffer and not adding 1 (because this bit is zero)
         data = data << 1;
 
@@ -157,8 +156,8 @@
         cnt++;
     }
 
-    // Detecting 1 if the pulse width ranges from 60 us to 80 us
-    else if (60 <= t_pulse_us && t_pulse_us <= 80) {
+    // Detecting 1 if the pulse width ranges from 70 us
+    else if (70 - t_tol_pulse <= t_pulse_us && t_pulse_us <= 70 + t_tol_pulse) {
         // Shifting the data buffer and adding 1 (because this bit is one)
         data = data << 1;
         data++;

--- a/DHT11.h	Wed Sep 10 18:00:31 2014 +0000
+++ b/DHT11.h	Thu Sep 11 13:45:00 2014 +0000
@@ -28,7 +28,7 @@
  */
 
 class DHT11
-{
+{   
 public:
     /** Create a DHT11 interface
      * @param pin 1-wire-like serial I/O port of DHT11
@@ -49,20 +49,20 @@
     int readData(void);
 
     /** Reading the humidity from the data
-     * @return Humidity in % if readData() returns no error.
-     * Otherwise, returns 0xffffffff.
+     * @return Humidity in %,
+     * regardless of the error from readData()
      */
     int readHumidity(void);
 
     /** Reading the temperature from the data
-     * @return Temperature in Celcius if readData() returns no error.
-     * Otherwise, returns 0xffffffff.
+     * @return Temperature in Celcius,
+     * regardless of the error from readData()
      */
     int readTemperature(void);
 
     enum ErrorDHT11 {
         OK = 0,
-        TOO_FAST_READ = 1,
+        READ_TOO_OFTEN = 1,
         BUS_BUSY = 2,
         NOT_PRESENT = 3,
         NOT_READY = 4,
@@ -75,13 +75,14 @@
     InterruptIn io_irq;
     Timer t;
     uint32_t t_pulse_us;
+    const static int t_tol_start;    
+    const static int t_tol_pulse;
     bool first_time;
     uint64_t data;
     uint32_t chksum;
     uint32_t cnt;
     uint32_t wdt;
     bool eod;
-    ErrorDHT11 err;
     void init(void);
     void pos_edge(void);
     void neg_edge(void);