Andy Pomfret / DHT11

Simple library for the DHT11 temperature and humidity sensor. Forked from an existing Mbed DHT11 project.

Dependents:   UoY-DHT11-test

Simple DHT11 temperature and humidity library.

Example usage

#include "mbed.h"
#include "DHT11.h"

DHT11 dht(D8); // Change pin name here if required

main()
{
    printf("T:%d, H:%d\r\n", dht.readTemperature(), dht.readHumidity());
}

The sensor may be read as often as desired, but temperature and humidity values are cached and will only be updated if they are more than 2 seconds old. This is the underlying sensor update rate.

Please note that this project has been modified only enough to make it work for its intended purpose. Various parts of this project still need work, and the source code should not be seen as an example of best practice.

Diff: DHT11.cpp

Revision:
13:11d0770eb603
Parent:
12:af1eadec17e5
--- a/DHT11.cpp	Mon May 31 07:02:00 2021 +0000
+++ b/DHT11.cpp	Wed Sep 15 14:47:06 2021 +0000
@@ -1,4 +1,5 @@
 /* Copyright (c) 2014 Shigenori Inoue, MIT License
+ * Modified by Andy Pomfret 2021
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software 
  * and associated documentation files (the "Software"), to deal in the Software without restriction, 
@@ -25,7 +26,7 @@
     io_irq.fall(callback(this, &DHT11::neg_edge));
     io_irq.disable_irq();
     t.start();
-    first_time = true;
+    readNewData();
 }
 
 // Destructor
@@ -39,10 +40,10 @@
 int DHT11::readData(void)
 {
     // Checking the measurement frequency
-    if (chrono::duration_cast<chrono::milliseconds>(t.elapsed_time()).count() < 2000 && first_time == false) {
-        t.reset();
-        return READ_TOO_OFTEN;
-    }
+//    if (chrono::duration_cast<chrono::milliseconds>(t.elapsed_time()).count() < 2000) {
+//        t.reset();
+//        return READ_TOO_OFTEN;
+//    }
     
     // Initialize
     init();
@@ -57,8 +58,7 @@
     t.reset();
     io.output();
     io = 0;
-    do {
-    } while (chrono::duration_cast<chrono::milliseconds>(t.elapsed_time()).count() < 20 + t_tol_start);
+    thread_sleep_for(10 + t_tol_start);
     io.input();
     io = 1;
     
@@ -72,7 +72,7 @@
         }
     } while (io == 1);
 
-    // Wainting for the start of the ready signal
+    // Waiting for the start of the ready signal
     t.reset();
     do {
         if (t.elapsed_time().count() > 100) {
@@ -81,7 +81,7 @@
         }
     } while (io == 0);
 
-    // Wainting for the end of the ready signal
+    // Waiting for the end of the ready signal
     t.reset();
     do {
         if (t.elapsed_time().count() > 100) {
@@ -91,7 +91,7 @@
     } while (io == 1);
 
     // Starting the pulse width sensing
-    // by the use of interruptions
+    // by the use of interrupts
     io_irq.enable_irq();
 
     do {
@@ -104,30 +104,39 @@
     } while (eod == false);
 
     // Calculating the check sum
-    chksum = ((data & 0xff00000000) >> 32)
-             + ((data & 0x00ff000000) >> 24)
-             + ((data & 0x0000ff0000) >> 16)
-             + ((data & 0x000000ff00) >> 8);
+    chksum = (data >> 32)
+             + (data >> 24)
+             + (data >> 16)
+             + (data >> 8);
 
-    if (chksum != (data & 0x00000000ff)) {
+    if ((chksum & 0xff) != (data & 0x00000000ff)) {
         t.reset();
         return CHKSUM_ERR;
     } else {
         t.reset();
-        first_time = false;
         return OK;
     }
 }
 
+void DHT11::readNewData(void) {
+    do; while (readData() != OK);
+}
+
 // Extracting humidity data from the received data
 int DHT11::readHumidity(void)
 {
+    if (t.elapsed_time() >= 2000ms) {
+        readNewData();
+    }
     return (data & 0xff00000000) >> 32;
 }
 
 // Extracting temperature data from the received data
 int DHT11::readTemperature(void)
 {
+    if (t.elapsed_time() >= 2000ms) {
+        readNewData();
+    }
     return (data & 0x0000ff0000) >> 16;
 }
 
@@ -145,19 +154,19 @@
 
 void DHT11::pos_edge(void)
 {
-    // Disabling the interruptions
+    // Disabling the interrupts
     io_irq.disable_irq();
 
     // Initializing the Timer
     t.reset();
 
-    // Enabling the interruptions
+    // Enabling the interrupts
     io_irq.enable_irq();
 }
 
 void DHT11::neg_edge(void)
 {
-    // Disabling the interruptions
+    // Disabling the interrupts
     io_irq.disable_irq();
 
     // Reading the positive pulse width