GroveDht22.h

00001 #ifndef __GROVE_DHT_22_H__
00002 #define __GROVE_DHT_22_H__
00003 
00004 #include "DHT.h"
00005 #include "mbed.h"
00006 #include "AbstractHandler.h"
00007 
00008 class MeasurementHandler;
00009 
00010 /*!
00011  * \brief The Dht22Result struct is the information read from a Dht22 Grove sensor
00012  */
00013 struct Dht22Result {
00014     time_t resultTime;      ///< timestamp of when the result was returned from the Dht22
00015     float  lastCelcius;     ///< Temperature result (degC)
00016     float  lastHumidity;    ///< Humidity result
00017     float  lastDewpoint;    ///< Dewpoint result
00018 };
00019 
00020 /*!
00021  * \brief The GroveDht22 class handles the interface to the DHT22 humidity and temperature sensor.
00022  *
00023  * The state machine checks for errors and retries and will power cycle the sensor if there are
00024  * GROVE_NUM_RETRIES number of retries.
00025 
00026  * The state machine also ensures that at least two seconds is left between readings.
00027 
00028  * At any time the parent class can access the last good readings, or the last error.
00029 
00030  * The newInfo flag exists so that the parent can decide to only notify (print to terminal or otherwise) when there
00031  * is new information available. Calling the newInfo getter will clear the newInfo flag.
00032  */
00033 class GroveDht22 : public AbstractHandler
00034 {
00035 public:
00036     GroveDht22(MeasurementHandler *_measure, MyTimers * _timer);
00037     ~GroveDht22();
00038 
00039     void run();
00040 
00041     void setRequest(int request, void *data = 0);
00042 
00043     // getters
00044     float  lastCelcius()  { return _lastCelcius; }
00045     float  lastHumidity() { return _lastHumidity; }
00046     float  lastDewPoint() { return _lastDewpoint; }
00047     eError lastError()    { return _lastError; }
00048     unsigned char newInfo();
00049 
00050 private:
00051     // state machine
00052     typedef enum {
00053         dht_StartTurnOff,       ///< Begin by ensuring the sensor is switched off
00054         dht_StartTurnOffWait,   ///< Allow it to power down completely
00055         dht_StartTurnOn,        ///< Turn the sensor on
00056         dht_StartTurnOnWait,    ///< Allow sensor to settle after powering on
00057         dht_TakeMeasurement,    ///< Take a measurement, check if valid, update measurment vars, set newInfo
00058         dht_WaitMeasurement     ///< Wait for 2 seconds between measurements
00059     } mode_t;
00060 
00061     mode_t mode;            ///< The current state in the state machine
00062 
00063     float _lastCelcius;     ///< Last temperature reading from the Dht22 sensor
00064     float _lastHumidity;    ///< Last humidity reading from the Dht22 sensor
00065     float _lastDewpoint;    ///< Last dewpoint calculation from last temp, humidity vales
00066     unsigned char _newInfo; ///< This flag indicates there is new information (an error, or a measurement)
00067     int _retries;           ///< Number of bad readings from the Dht22 sensor
00068     eError _lastError;      ///< The last error, or lack thereof
00069 
00070     /*!
00071      * \brief powerOn powers the Dht22 on or off, by toggling the enable pin
00072      * \param ON true to power on, false to power off
00073      */
00074     void powerOn(unsigned char ON);
00075 
00076     MeasurementHandler *m_measure;  ///< Reference to send measurement results and errors to for handling
00077 
00078     DHT *m_sensor;                  ///< Interface to hardware DHT sensor
00079 };
00080 
00081 #endif // __GROVE_DHT_22_H__