Diff: DHT11.cpp

Revision:

0:4d4c5ea17d86

Child:

1:95b80cc3f676

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/DHT11.cpp	Wed Sep 10 15:14:31 2014 +0000
@@ -0,0 +1,186 @@
+/** @file
+ Library for the use of the DHT11, a temperature and humidity sensor
+ Shigenori Inoue, September 10, 2014
+ */
+
+#include "DHT11.h"
+
+// Constructor
+DHT11::DHT11(PinName pin) : io(pin, PIN_INPUT, OpenDrain, 1), io_irq(pin)
+{
+    io_irq.rise(this, &DHT11::pos_edge);
+    io_irq.fall(this, &DHT11::neg_edge);
+    io_irq.disable_irq();
+    init();
+}
+
+// Destructor
+DHT11::~DHT11(void) {}
+
+// Reading the data bits from DHT11
+int DHT11::readData()
+{
+    // Initialize
+    eod = false;
+    err = OK;
+    data = 0;
+    cnt = 0;
+    wdt = 0;
+
+    // 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();
+        return BUS_BUSY;
+    }
+
+    // Sending start signal
+    io.output();
+    t.reset();
+    t.start();
+    do {
+        io = 0;
+    } while (t.read_ms() < 18);
+    io.input();
+    io = 1;
+
+    // Waiting for the start of the response signal
+    t.reset();
+    t.start();
+    do {
+        if (t.read_us() > 100) {
+            io.input();
+            io = 1;
+            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();
+            io = 1;
+            return NOT_READY;
+        }
+    } while (io == 0);
+
+    // Wainting for the end of the ready signal
+    t.reset();
+    t.start();
+    do {} while (io == 1);
+
+    // Starting the pulse width sensing
+
+    io_irq.enable_irq();
+
+    do {
+        wait_us(100);
+        if (wdt > 50) {
+            return WATCHDOG_ERR;
+        }
+        wdt++;
+    } while (eod == false);
+
+    // Calculating the check sum
+    chksum = ((data & 0xff00000000) >> 32)
+             + ((data & 0x00ff000000) >> 24)
+             + ((data & 0x0000ff0000) >> 16)
+             + ((data & 0x000000ff00) >> 8);
+    if (chksum != (data & 0x00000000ff)) {
+        io.input();
+        io = 1;
+        return CHKSUM_ERR;
+    } else {
+        t.reset();
+        first_time = false;
+        return OK;
+    }
+}
+
+// Extracting humidity data from the received data
+int DHT11::readHumidity()
+{
+    if (err == OK) {
+        return (data & 0xff00000000) >> 32;
+    } else {
+        return 0xffffffff;
+    }
+}
+
+// Extracting temperature data from the received data
+int DHT11::readTemperature()
+{
+    if (err == OK) {
+        return (data & 0x0000ff0000) >> 16;
+    } else {
+        return 0xffffffff;
+    }
+}
+
+// Initialization of variables
+void DHT11::init(void)
+{
+    t_pulse_us = 0;
+    first_time = true;
+    data = 0;
+    chksum = 0;
+    cnt = 0;
+    wdt = 0;
+    err = OK;
+    eod = false;
+}
+
+void DHT11::pos_edge(void)
+{
+    // Disabling the interruptions
+    io_irq.disable_irq();
+
+    // Initializing the Timer
+    t.reset();
+
+    // Enabling the interruptions
+    io_irq.enable_irq();
+}
+
+void DHT11::neg_edge(void)
+{
+    // Disabling the interruptions
+    io_irq.disable_irq();
+
+    // Reading the length of
+    t_pulse_us = t.read_us();
+
+    // Detecting 0 if the pulse width ranges from 26 us to 28 us
+    if (20 <= t_pulse_us && t_pulse_us <= 30) {
+        // Shifting the data buffer and not adding 1 (because this bit is zero)
+        data = data << 1;
+
+        // Counting up the bits
+        cnt++;
+    }
+
+    // Detecting 1 if the pulse width ranges from 68 us to 72 us
+    else if (60 <= t_pulse_us && t_pulse_us <= 80) {
+        // Shifting the data buffer and adding 1 (because this bit is one)
+        data = data << 1;
+        data++;
+
+        // Counting up the bits
+        cnt++;
+    }
+
+    // Detecting the end of Data
+    if (cnt < 40) {
+        // Enabling the interruptions
+        io_irq.enable_irq();
+    } else {
+        eod = true;
+    }
+}
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