Andy Pomfret / DHT11

Simple library for the DHT11 temperature and humidity sensor. Forked from an existing Mbed DHT11 project.

Dependents:   UoY-DHT11-test

Simple DHT11 temperature and humidity library.

Example usage

#include "mbed.h"
#include "DHT11.h"

DHT11 dht(D8); // Change pin name here if required

main()
{
    printf("T:%d, H:%d\r\n", dht.readTemperature(), dht.readHumidity());
}

The sensor may be read as often as desired, but temperature and humidity values are cached and will only be updated if they are more than 2 seconds old. This is the underlying sensor update rate.

Please note that this project has been modified only enough to make it work for its intended purpose. Various parts of this project still need work, and the source code should not be seen as an example of best practice.

DHT11.h

Committer:
ajp109
Date:
2021-09-15
Revision:
13:11d0770eb603
Parent:
12:af1eadec17e5

File content as of revision 13:11d0770eb603:

/* 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.
 */
 
#ifndef __DHT11__
#define __DHT11__
#include "mbed.h"

/**  Example:
 * @code
 * #include "mbed.h"
 * #include "DHT11.h"
 *
 * DHT11 d(D8); // Here fill your PIN mask/name
 *
 * main()
 * {
 *     printf("T:%d, H:%d\r\n", d.readTemperature(), d.readHumidity());
 * }
 * @endcode
 */

class DHT11
{   
public:
    /** Create a DHT11 interface
     * @param pin 1-wire-like serial I/O port of DHT11
     */
    DHT11(PinName pin);
    ~DHT11();

    /** Reading the data from the DHT11.  Calling this is not required, but
     * may be useful for debug.
     * @return Error code
     *     0: OK.
     *     1: Reading the data too often.
     *     2: 1-wire bus is busy.
     *     3: DHT11 does not respond.
     *     4: DHT11 is not ready.
     *     5: Checksum is incorrect.
     *     6: Timeout.
     */
    int readData(void);

    /** Returns the current humidity from the DHT11.  If the existing data record
     * is older than 2000ms, initiates a read from the device.  Note that errors
     * may result in infinite attempts to read.
     * @return Humidity in %
     */
    int readHumidity(void);

    /** Returns the current temperature from the DHT11.  If the existing data record
     * is older than 2000ms, initiates a read from the device.  Note that errors
     * may result in infinite attempts to read.
     * @return Temperature in Celcius
     */
    int readTemperature(void);

    enum ErrorDHT11 {
        OK = 0,
        READ_TOO_OFTEN = 1,
        BUS_BUSY = 2,
        NOT_PRESENT = 3,
        NOT_READY = 4,
        CHKSUM_ERR = 5,
        WATCHDOG_ERR = 6,
    };

private:
    DigitalInOut io;
    InterruptIn io_irq;
    Timer t;
    uint32_t t_pulse_us;
    const static int t_tol_start;    
    const static int t_tol_pulse;
    uint64_t data;
    uint32_t chksum;
    uint32_t cnt;
    uint32_t wdt;
    bool eod;
    void init(void);
    void pos_edge(void);
    void neg_edge(void);
    void readNewData(void);
};

#endif