Diff: DHT/Mbed_DHT.cpp

Revision:

1:e7f73d96ddde

Parent:

0:a935d23434d9

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/DHT/Mbed_DHT.cpp	Fri Jun 28 17:52:12 2019 +0000
@@ -0,0 +1,224 @@
+/*
+ *  DHT Library for  Digital-output Humidity and Temperature sensors
+ *
+ *  Works with DHT11, DHT22
+ *             SEN11301P,  Grove - Temperature&Humidity Sensor     (Seeed Studio)
+ *             SEN51035P,  Grove - Temperature&Humidity Sensor Pro (Seeed Studio)
+ *             AM2302   ,  temperature-humidity sensor
+ *             HM2303   ,  Digital-output humidity and temperature sensor
+ *
+ *  Copyright (C) Wim De Roeve
+ *                based on DHT22 sensor library by HO WING KIT
+ *                Arduino DHT11 library
+ *
+ * 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.
+ */
+ 
+#include "Mbed_DHT.h"
+ 
+#define DHT_DATA_BIT_COUNT 40
+ 
+DHT::DHT(PinName pin, eType DHTtype)
+{
+    _pin = pin;
+    _DHTtype = DHTtype;
+    _firsttime = true;
+}
+ 
+DHT::~DHT()
+{
+    
+}
+ 
+eError DHT::stall(DigitalInOut &io, int const level, int const max_time)
+{
+    int cnt = 0;
+    while (level == io) {
+        if (cnt > max_time) {
+            return ERROR_NO_PATIENCE;
+        }
+        cnt++;
+        wait_us(1);
+    }
+    return ERROR_NONE;
+}
+ 
+eError DHT::readData()
+{
+    uint8_t i = 0, j = 0, b = 0, data_valid = 0;
+    uint32_t bit_value[DHT_DATA_BIT_COUNT] = {0};
+ 
+    eError err = ERROR_NONE;
+    time_t currentTime = time(NULL);
+ 
+    DigitalInOut DHT_io(_pin);
+ 
+    // IO must be in hi state to start
+    if (ERROR_NONE != stall(DHT_io, 0, 250)) {
+        return BUS_BUSY;
+    }
+ 
+    // start the transfer
+    DHT_io.output();
+    DHT_io = 0;
+    wait_ms(18);
+    DHT_io = 1;
+    wait_us(30);
+    DHT_io.input();
+    // wait till the sensor grabs the bus
+    if (ERROR_NONE != stall(DHT_io, 1, 100)) {
+        return ERROR_NOT_PRESENT;
+    }
+    // sensor should signal low 80us and then hi 80us
+    if (ERROR_NONE != stall(DHT_io, 0, 100)) {
+        return ERROR_SYNC_TIMEOUT;
+    }
+    if (ERROR_NONE != stall(DHT_io, 1, 100)) {
+        return ERROR_NO_PATIENCE;
+    }
+    // capture the data
+    for (i = 0; i < 5; i++) {
+        for (j = 0; j < 8; j++) {
+            if (ERROR_NONE != stall(DHT_io, 0, 75)) {
+                return ERROR_DATA_TIMEOUT;
+            }
+            // logic 0 is 28us max, 1 is 70us
+            wait_us(40);
+            bit_value[i*8+j] = DHT_io;
+            if (ERROR_NONE != stall(DHT_io, 1, 50)) {
+                return ERROR_DATA_TIMEOUT;
+            }
+        }
+    }
+    // store the data
+    for (i = 0; i < 5; i++) {
+        b=0;
+        for (j=0; j<8; j++) {
+            if (bit_value[i*8+j] == 1) {
+                b |= (1 << (7-j));
+            }
+        }
+        DHT_data[i]=b;
+    }
+ 
+    // uncomment to see the checksum error if it exists
+    //printf(" 0x%02x + 0x%02x + 0x%02x + 0x%02x = 0x%02x \n", DHT_data[0], DHT_data[1], DHT_data[2], DHT_data[3], DHT_data[4]);
+    data_valid = DHT_data[0] + DHT_data[1] + DHT_data[2] + DHT_data[3];
+    if (DHT_data[4] == data_valid) {
+        _lastReadTime = currentTime;
+        _lastTemperature = CalcTemperature();
+        _lastHumidity = CalcHumidity();
+ 
+    } else {
+        err = ERROR_CHECKSUM;
+    }
+ 
+    return err;
+ 
+}
+ 
+float DHT::CalcTemperature()
+{
+    int v;
+ 
+    switch (_DHTtype) {
+        case DHT11:
+            v = DHT_data[2];
+            return float(v);
+        case DHT22:
+            v = DHT_data[2] & 0x7F;
+            v *= 256;
+            v += DHT_data[3];
+            v /= 10;
+            if (DHT_data[2] & 0x80)
+                v *= -1;
+            return float(v);
+    }
+    return 0;
+}
+ 
+float DHT::ReadHumidity()
+{
+    return _lastHumidity;
+}
+ 
+float DHT::ConvertCelciustoFarenheit(float const celsius)
+{
+    return celsius * 9 / 5 + 32;
+}
+ 
+float DHT::ConvertCelciustoKelvin(float const celsius)
+{
+    return celsius + 273.15f;
+}
+ 
+// dewPoint function NOAA
+// reference: http://wahiduddin.net/calc/density_algorithms.htm
+float DHT::CalcdewPoint(float const celsius, float const humidity)
+{
+    float A0= 373.15f/(273.15f + celsius);
+    float SUM = -7.90298 * (A0-1);
+    SUM += 5.02808f * log10(A0);
+    SUM += -1.3816e-7 * (pow(10, (11.344f*(1-1/A0)))-1) ;
+    SUM += 8.1328e-3 * (pow(10,(-3.49149*(A0-1)))-1) ;
+    SUM += log10(1013.246);
+    float VP = pow(10, SUM-3) * humidity;
+    float T = log(VP/0.61078f);   // temp var
+    return (241.88f * T) / (17.558f-T);
+}
+ 
+// delta max = 0.6544 wrt dewPoint()
+// 5x faster than dewPoint()
+// reference: http://en.wikipedia.org/wiki/Dew_point
+float DHT::CalcdewPointFast(float const celsius, float const humidity)
+{
+    float a = 17.271;
+    float b = 237.7;
+    float temp = (a * celsius) / (b + celsius) + log(humidity/100);
+    float Td = (b * temp) / (a - temp);
+    return Td;
+}
+ 
+float DHT::ReadTemperature(eScale Scale)
+{
+    if (Scale == FARENHEIT)
+        return ConvertCelciustoFarenheit(_lastTemperature);
+    else if (Scale == KELVIN)
+        return ConvertCelciustoKelvin(_lastTemperature);
+    else
+        return _lastTemperature;
+}
+ 
+float DHT::CalcHumidity()
+{
+    int v;
+ 
+    switch (_DHTtype) {
+        case DHT11:
+            v = DHT_data[0];
+            return float(v);
+        case DHT22:
+            v = DHT_data[0];
+            v *= 256;
+            v += DHT_data[1];
+            v /= 10;
+            return float(v);
+    }
+    return 0;
+}
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