Diff: AM2303.cpp

Revision:

12:1ad0612823e9

Parent:

11:e91c151d1798

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/AM2303.cpp	Mon Oct 13 14:18:58 2014 +0000
@@ -0,0 +1,192 @@
+/* Copyright (c) 2014 Shigenori Inoue, MIT License
+ *
+ * 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,
+ * 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
+ * furnished 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 FOR 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.
+ */
+
+#include "AM2303.h"
+
+// Constructor
+AM2303::AM2303(PinName pin) : io(pin, PIN_INPUT, OpenDrain, 1), io_irq(pin)
+{
+    io_irq.rise(this, &AM2303::pos_edge);
+    io_irq.fall(this, &AM2303::neg_edge);
+    io_irq.disable_irq();
+    io_irq.mode(OpenDrain);
+    t.start();
+    first_time = true;
+}
+
+// Destructor
+AM2303::~AM2303(void) {}
+
+// Constants
+const int AM2303::t_tol_start = 100;
+const int AM2303::t_tol_pulse = 10;
+
+// Reading the data bits from the AM2303
+int AM2303::readData(void)
+{
+    // Checking the measurement frequency
+    if (t.read_ms() < 2000 && first_time == false) {
+        t.reset();
+        return READ_TOO_OFTEN;
+    }
+
+    // Initialize
+    init();
+
+    // Checking the data bus
+    if (io == 0) {
+        t.reset();
+        return BUS_BUSY;
+    }
+
+    // Sending start signal, low signal for around 10 ms
+    t.reset();
+    io.output();
+    io = 0;
+    do {
+    } while (t.read_us() < 1000 + t_tol_start);
+    io.input();
+    io = 1;
+
+    // Waiting for the start of the response signal
+    t.reset();
+    do {
+        if (t.read_us() > 100) {
+            t.reset();
+            return NOT_PRESENT;
+        }
+    } while (io == 1);
+
+    // Wainting for the start of the ready signal
+    t.reset();
+    do {
+        if (t.read_us() > 100) {
+            t.reset();
+            return NOT_READY;
+        }
+    } while (io == 0);
+
+    // Wainting for the end of the ready signal
+    t.reset();
+    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++;
+    } while (eod == false);
+
+    // Calculating the check sum
+    chksum = ((data & 0xff00000000) >> 32)
+             + ((data & 0x00ff000000) >> 24)
+             + ((data & 0x0000ff0000) >> 16)
+             + ((data & 0x000000ff00) >> 8);
+
+    if ((chksum & 0xff) != (data & 0x00000000ff)) {
+        t.reset();
+        return CHKSUM_ERR;
+    } else {
+        t.reset();
+        first_time = false;
+        return OK;
+    }
+}
+
+// Extracting humidity data from the received data
+float AM2303::readHumidity(void)
+{
+    return static_cast<float>((data & 0xffff000000) >> 24) / 10;
+}
+
+// Extracting temperature data from the received data
+float AM2303::readTemperature(void)
+{
+    return static_cast<float>((data & 0x0000ffff00) >> 8) / 10;
+}
+
+// Initialization of variables
+void AM2303::init(void)
+{
+    t_pulse_us = 0;
+    data = 0;
+    chksum = 0;
+    cnt = 0;
+    wdt = 0;
+    eod = false;
+    t.reset();
+}
+
+void AM2303::pos_edge(void)
+{
+    // Disabling the interruptions
+    io_irq.disable_irq();
+
+    // Initializing the Timer
+    t.reset();
+
+    // Enabling the interruptions
+    io_irq.enable_irq();
+}
+
+void AM2303::neg_edge(void)
+{
+    // Disabling the interruptions
+    io_irq.disable_irq();
+
+    // Reading the positive pulse width
+    t_pulse_us = t.read_us();
+
+    // 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;
+
+        // Counting up the bits
+        cnt++;
+    }
+
+    // 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++;
+
+        // 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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