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@9:056d1e9b428c, 2014-09-11 (annotated)

Committer:
s_inoue_mbed
Date:
Thu Sep 11 13:45:00 2014 +0000
Revision:
9:056d1e9b428c
Parent:
5:da586c935e88
Child:
10:f0d789f49df7
Bug fix

Who changed what in which revision?

UserRevisionLine numberNew contents of line
s_inoue_mbed 4:48798b126d93 1 /*
s_inoue_mbed 4:48798b126d93 2 * Library for the use of the DHT11, a temperature and humidity sensor
s_inoue_mbed 4:48798b126d93 3 * Shigenori Inoue, September 10, 2014
s_inoue_mbed 0:4d4c5ea17d86 4 */
s_inoue_mbed 0:4d4c5ea17d86 5 #ifndef __DHT11__
s_inoue_mbed 0:4d4c5ea17d86 6 #define __DHT11__
s_inoue_mbed 0:4d4c5ea17d86 7 #include "mbed.h"
s_inoue_mbed 0:4d4c5ea17d86 8
s_inoue_mbed 0:4d4c5ea17d86 9 /** Example:
s_inoue_mbed 0:4d4c5ea17d86 10 * @code
s_inoue_mbed 0:4d4c5ea17d86 11 * #include "mbed.h"
s_inoue_mbed 0:4d4c5ea17d86 12 * #include "DHT11.h"
s_inoue_mbed 0:4d4c5ea17d86 13 *
s_inoue_mbed 0:4d4c5ea17d86 14 * DHT11 d;
s_inoue_mbed 0:4d4c5ea17d86 15 *
s_inoue_mbed 0:4d4c5ea17d86 16 * main()
s_inoue_mbed 0:4d4c5ea17d86 17 * {
s_inoue_mbed 0:4d4c5ea17d86 18 * int s;
s_inoue_mbed 0:4d4c5ea17d86 19 * s = d.readData();
s_inoue_mbed 2:1e997b7a1f9a 20 * if (s != DHT11::OK) {
s_inoue_mbed 0:4d4c5ea17d86 21 * printf("Error!\r\n");
s_inoue_mbed 0:4d4c5ea17d86 22 * }
s_inoue_mbed 0:4d4c5ea17d86 23 * else {
s_inoue_mbed 0:4d4c5ea17d86 24 * printf("T:%d, H:%d\r\n", d.readTemperature(), d.readHumidity());
s_inoue_mbed 0:4d4c5ea17d86 25 * }
s_inoue_mbed 0:4d4c5ea17d86 26 * }
s_inoue_mbed 0:4d4c5ea17d86 27 * @endcode
s_inoue_mbed 0:4d4c5ea17d86 28 */
s_inoue_mbed 0:4d4c5ea17d86 29
s_inoue_mbed 0:4d4c5ea17d86 30 class DHT11
s_inoue_mbed 9:056d1e9b428c 31 {
s_inoue_mbed 0:4d4c5ea17d86 32 public:
s_inoue_mbed 0:4d4c5ea17d86 33 /** Create a DHT11 interface
s_inoue_mbed 0:4d4c5ea17d86 34 * @param pin 1-wire-like serial I/O port of DHT11
s_inoue_mbed 0:4d4c5ea17d86 35 */
s_inoue_mbed 0:4d4c5ea17d86 36 DHT11(PinName pin);
s_inoue_mbed 0:4d4c5ea17d86 37 ~DHT11();
s_inoue_mbed 0:4d4c5ea17d86 38
s_inoue_mbed 0:4d4c5ea17d86 39 /** Reading the data from the DHT11
s_inoue_mbed 0:4d4c5ea17d86 40 * @return Error code
s_inoue_mbed 0:4d4c5ea17d86 41 * 0: OK.
s_inoue_mbed 0:4d4c5ea17d86 42 * 1: Reading the data too often.
s_inoue_mbed 0:4d4c5ea17d86 43 * 2: 1-wire bus is busy.
s_inoue_mbed 0:4d4c5ea17d86 44 * 3: DHT11 does not respond.
s_inoue_mbed 0:4d4c5ea17d86 45 * 4: DHT11 is not ready.
s_inoue_mbed 0:4d4c5ea17d86 46 * 5: Checksum is incorrect.
s_inoue_mbed 5:da586c935e88 47 * 6: Timeout.
s_inoue_mbed 0:4d4c5ea17d86 48 */
s_inoue_mbed 3:8cd064147bde 49 int readData(void);
s_inoue_mbed 3:8cd064147bde 50
s_inoue_mbed 0:4d4c5ea17d86 51 /** Reading the humidity from the data
s_inoue_mbed 9:056d1e9b428c 52 * @return Humidity in %,
s_inoue_mbed 9:056d1e9b428c 53 * regardless of the error from readData()
s_inoue_mbed 0:4d4c5ea17d86 54 */
s_inoue_mbed 0:4d4c5ea17d86 55 int readHumidity(void);
s_inoue_mbed 3:8cd064147bde 56
s_inoue_mbed 3:8cd064147bde 57 /** Reading the temperature from the data
s_inoue_mbed 9:056d1e9b428c 58 * @return Temperature in Celcius,
s_inoue_mbed 9:056d1e9b428c 59 * regardless of the error from readData()
s_inoue_mbed 0:4d4c5ea17d86 60 */
s_inoue_mbed 0:4d4c5ea17d86 61 int readTemperature(void);
s_inoue_mbed 3:8cd064147bde 62
s_inoue_mbed 0:4d4c5ea17d86 63 enum ErrorDHT11 {
s_inoue_mbed 0:4d4c5ea17d86 64 OK = 0,
s_inoue_mbed 9:056d1e9b428c 65 READ_TOO_OFTEN = 1,
s_inoue_mbed 0:4d4c5ea17d86 66 BUS_BUSY = 2,
s_inoue_mbed 0:4d4c5ea17d86 67 NOT_PRESENT = 3,
s_inoue_mbed 0:4d4c5ea17d86 68 NOT_READY = 4,
s_inoue_mbed 0:4d4c5ea17d86 69 CHKSUM_ERR = 5,
s_inoue_mbed 0:4d4c5ea17d86 70 WATCHDOG_ERR = 6,
s_inoue_mbed 0:4d4c5ea17d86 71 };
s_inoue_mbed 0:4d4c5ea17d86 72
s_inoue_mbed 0:4d4c5ea17d86 73 private:
s_inoue_mbed 0:4d4c5ea17d86 74 DigitalInOut io;
s_inoue_mbed 0:4d4c5ea17d86 75 InterruptIn io_irq;
s_inoue_mbed 0:4d4c5ea17d86 76 Timer t;
s_inoue_mbed 0:4d4c5ea17d86 77 uint32_t t_pulse_us;
s_inoue_mbed 9:056d1e9b428c 78 const static int t_tol_start;
s_inoue_mbed 9:056d1e9b428c 79 const static int t_tol_pulse;
s_inoue_mbed 0:4d4c5ea17d86 80 bool first_time;
s_inoue_mbed 0:4d4c5ea17d86 81 uint64_t data;
s_inoue_mbed 0:4d4c5ea17d86 82 uint32_t chksum;
s_inoue_mbed 0:4d4c5ea17d86 83 uint32_t cnt;
s_inoue_mbed 0:4d4c5ea17d86 84 uint32_t wdt;
s_inoue_mbed 0:4d4c5ea17d86 85 bool eod;
s_inoue_mbed 0:4d4c5ea17d86 86 void init(void);
s_inoue_mbed 0:4d4c5ea17d86 87 void pos_edge(void);
s_inoue_mbed 0:4d4c5ea17d86 88 void neg_edge(void);
s_inoue_mbed 0:4d4c5ea17d86 89 };
s_inoue_mbed 0:4d4c5ea17d86 90
s_inoue_mbed 0:4d4c5ea17d86 91 #endif