Diff: DHT/DHT.cpp

Revision:

0:b1384299f31c

Child:

1:6df9454191d4

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/DHT/DHT.cpp	Fri Dec 21 03:20:04 2018 +0000
@@ -0,0 +1,212 @@
+
+
+#include "DHT.h"
+
+#define DHT_DATA_BIT_COUNT 41
+
+DHT::DHT(PinName pin,int DHTtype) {
+    _pin = pin;
+    _DHTtype = DHTtype;
+    _firsttime=true;
+}
+
+DHT::~DHT() {
+}
+
+int DHT::readData() {
+    int i, j, retryCount,b;
+    unsigned int bitTimes[DHT_DATA_BIT_COUNT];
+
+    eError err = ERROR_NONE;
+    uint32_t currentTime = us_ticker_read() / 1000000;
+
+    DigitalInOut DHT_io(_pin);
+
+    //Clear the bit buffer. 
+    for (i = 0; i < DHT_DATA_BIT_COUNT; i++) {
+        bitTimes[i] = 0;
+    }
+
+    if (!_firsttime) {
+        if (int(currentTime - _lastReadTime) < 2) {
+            err = ERROR_NO_PATIENCE;
+            return err;
+        }
+    } else {
+        _firsttime = false;
+        _lastReadTime = currentTime;
+    }
+    retryCount = 0;
+
+    do {
+        if (retryCount > 125) {
+            err = BUS_BUSY;
+            return err;
+        }
+        retryCount++;
+        wait_us(2);
+    } while (DHT_io == 0);
+
+
+    //Set pin as output
+    DHT_io.output(); 
+    //Put the Line as High impedance 
+    DHT_io = 1;
+    wait_ms(250);
+    
+    //Start of message.
+    DHT_io = 0;
+    wait_ms(20);
+
+    DHT_io = 1;
+    wait_us(40);
+    //Set line as input
+    DHT_io.input();
+
+    wait_us(10);
+    
+    retryCount = 0;
+
+    do {
+        if (retryCount > 40)  {
+            err = ERROR_NOT_PRESENT;
+            return err;
+        }
+        retryCount++;
+        wait_us(1);
+    } while ( DHT_io == 1 );
+
+    if (err != ERROR_NONE) {
+        return err;
+    }
+
+    for (i = 0; i < 5; i++) {
+        for (j = 0; j < 8; j++) {
+            retryCount = 0;
+            do {
+                if (retryCount > 78)  {
+                    err = ERROR_DATA_TIMEOUT;
+                    return err;
+                }
+                retryCount++;
+                wait_us(1);
+            } while (DHT_io == 0);
+            wait_us(40);
+            bitTimes[i*8+j] = DHT_io;
+
+            int count = 0;
+            while (DHT_io == 1 && count < 100) {
+                wait_us(1);
+                count++;
+            }
+        }
+    }
+    DHT_io.output();
+    DHT_io = 1;
+    for (i = 0; i < 5; i++) {
+        b=0;
+        for (j=0; j<8; j++) {
+            if (bitTimes[i*8+j+1] > 0) {
+                b |= ( 1 << (7-j));
+            }
+        }
+        DHT_data[i]=b;
+    }
+
+    if (DHT_data[4] == ((DHT_data[0] + DHT_data[1] + DHT_data[2] + DHT_data[3]) & 0xFF)) {
+        _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 celsius) {
+    return celsius * 9 / 5 + 32;
+}
+
+float DHT::ConvertCelciustoKelvin(float celsius) {
+    return celsius + 273.15;
+}
+
+// dewPoint function NOAA
+// reference: http://wahiduddin.net/calc/density_algorithms.htm
+float DHT::CalcdewPoint(float celsius, float humidity) {
+    float A0= 373.15/(273.15 + celsius);
+    float SUM = -7.90298 * (A0-1);
+    SUM += 5.02808 * log10(A0);
+    SUM += -1.3816e-7 * (pow(10, (11.344*(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/0.61078);   // temp var
+    return (241.88 * T) / (17.558-T);
+}
+
+// delta max = 0.6544 wrt dewPoint()
+// 5x faster than dewPoint()
+// reference: http://en.wikipedia.org/wiki/Dew_point
+float DHT::CalcdewPointFast(float celsius, float 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;
+}
+
+