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Dth11.h & cpp

#ifndef DHT11_H
#define DHT11_H

#include "mbed.h"

#define DHTLIB_OK                0
#define DHTLIB_ERROR_CHECKSUM   -1
#define DHTLIB_ERROR_TIMEOUT    -2

/** Class for the DHT11 sensor.
 * 
 * Example:
 * @code
 * #include "mbed.h"
 * #include "Dht11.h"
 *
 * Serial pc(USBTX, USBRX);
 * Dht11 sensor(PTD7);
 * 
 * int main() {
 *     sensor.read()
 *     pc.printf("T: %f, H: %d\r\n", sensor.getFahrenheit(), sensor.getHumidity());
 * }
 * @endcode
 */
class Dht11
{
public:
    /** Construct the sensor object.
     *
     * @param pin PinName for the sensor pin.
     */
    Dht11(PinName const &p);
    
    /** Update the humidity and temp from the sensor.
     *
     * @returns
     *   0 on success, otherwise error.
     */
    int read();
    
    /** Get the temp(f) from the saved object.
     *
     * @returns
     *   Fahrenheit float
     */
    float getFahrenheit();
    
    /** Get the temp(c) from the saved object.
     *
     * @returns
     *   Celsius int
     */
    int getCelsius();
    
    /** Get the humidity from the saved object.
     *
     * @returns
     *   Humidity percent int
     */
    int getHumidity();

private:
    /// percentage of humidity
    int _humidity;
    /// celsius
    int _temperature;
    /// pin to read the sensor info on
    DigitalInOut _pin;
    /// times startup (must settle for at least a second)
    Timer _timer;
};

#endif

#include "Dht11.h"

Dht11::Dht11(PinName const &p) : _pin(p) {
    // Set creation time so we can make 
    // sure we pause at least 1 second for 
    // startup.
    _timer.start();
    
    _temperature = 0;
    _humidity = 0;
}

int Dht11::read()
{
    // BUFFER TO RECEIVE
    uint8_t bits[5];
    uint8_t cnt = 7;
    uint8_t idx = 0;

    // EMPTY BUFFER
    for (int i=0; i< 5; i++) bits[i] = 0;
    
    // Verify sensor settled after boot
    while(_timer.read_ms() < 1500) {}
    _timer.stop();

    // Notify it we are ready to read
    _pin.output();
    _pin = 0;
    wait_ms(18);
    _pin = 1;
    wait_us(40);
    _pin.input();

    // ACKNOWLEDGE or TIMEOUT
    unsigned int loopCnt = 10000;
    while(_pin == 0)
        if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;

    loopCnt = 10000;
    while(_pin == 1)
        if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;

    // READ OUTPUT - 40 BITS => 5 BYTES or TIMEOUT
    for (int i=0; i<40; i++)
    {
        loopCnt = 10000;
        while(_pin == 0)
            if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;

        //unsigned long t = micros();
        Timer t;
        t. start();

        loopCnt = 10000;
        while(_pin == 1)
            if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;

        if (t.read_us() > 40) bits[idx] |= (1 << cnt);
        if (cnt == 0)   // next byte?
        {
            cnt = 7;    // restart at MSB
            idx++;      // next byte!
        }
        else cnt--;
    }

    // WRITE TO RIGHT VARS
    // as bits[1] and bits[3] are allways zero they are omitted in formulas.
    _humidity    = bits[0]; 
    _temperature = bits[2]; 

    uint8_t sum = bits[0] + bits[2];  

    if (bits[4] != sum) return DHTLIB_ERROR_CHECKSUM;
    return DHTLIB_OK;
}

float Dht11::getFahrenheit() {
    return((_temperature * 1.8) + 32);
}

int Dht11::getCelsius() {
    return(_temperature);
}

int Dht11::getHumidity() {
    return(_humidity);
}