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      1 /*
      2  * Author: Jon Trulson <jtrulson (at) ics.com>
      3  * Copyright (c) 2015 Intel Corporation.
      4  *
      5  * Permission is hereby granted, free of charge, to any person obtaining
      6  * a copy of this software and associated documentation files (the
      7  * "Software"), to deal in the Software without restriction, including
      8  * without limitation the rights to use, copy, modify, merge, publish,
      9  * distribute, sublicense, and/or sell copies of the Software, and to
     10  * permit persons to whom the Software is furnished to do so, subject to
     11  * the following conditions:
     12  *
     13  * The above copyright notice and this permission notice shall be
     14  * included in all copies or substantial portions of the Software.
     15  *
     16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
     17  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
     18  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
     19  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
     20  * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
     21  * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
     22  * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
     23  */
     24 #pragma once
     25 
     26 #include <iostream>
     27 #include <string>
     28 #include <mraa/aio.hpp>
     29 #include <mraa/gpio.hpp>
     30 
     31 namespace upm {
     32   /**
     33    * @brief DFRobot CO2 Sensor
     34    * @defgroup mg811 libupm-mg811
     35    * @ingroup dfrobot analog gas
     36    */
     37 
     38   /**
     39    * @library mg811
     40    * @sensor mg811
     41    * @comname DFRobot CO2 Sensor
     42    * @altname MG811
     43    * @type gas
     44    * @man dfrobot
     45    * @web http://www.dfrobot.com/index.php?route=product/product&product_id=1023
     46    * @con analog
     47    *
     48    * @brief API for the DFRobot CO2 Sensor
     49    *
     50    * This sensor returns an an analog voltage that falls as the
     51    * concentration of CO2 increases.  It contains a heater that must
     52    * be allowed to 'warm' up the sensor before measurements are stable
     53    * (hours to days is the recommendation).  It requires that the MCU
     54    * be powered from an external power supply (not USB) at 5v, since
     55    * the heater will consume significant current.
     56    *
     57    * The sensor should be allowed to 'heat' up for some time before
     58    * beginning use, typically a couple of hours minimum.  It also
     59    * needs fairly precise calibration at 400ppm and 1000ppm to return
     60    * meaningful results.
     61    *
     62    * The sensor also incorporates a potentiometer that can be adjusted
     63    * to specific threshold.  Once that threshold is reached, an LED
     64    * on the sensor will light, and the digital pin will be driven
     65    * high.
     66    *
     67    * @snippet mg811.cxx Interesting
     68    */
     69 
     70   class MG811 {
     71   public:
     72 
     73     /**
     74      * MG811 constructor
     75      *
     76      * @param pin Analog pin to use
     77      * @param dpin Digital pin that indicates threshold
     78      * @param aref Analog reference voltage; default is 5.0 V
     79      */
     80     MG811(int pin, int dpin, float aref=5.0);
     81 
     82     /**
     83      * MG811 destructor
     84      */
     85     ~MG811();
     86 
     87     /**
     88      * Return a cumputed reference voltage to be used in calibration.
     89      * @return Computed reference voltage
     90      */
     91     float getReferenceVoltage();
     92 
     93     /**
     94      * Set calibration parameters.  You should measure the reference
     95      * voltage you get when at CO2 concentrations of 400ppm (ambient)
     96      * and 1000ppm using the getReferenceVoltage() method.  Then
     97      * specify those voltages here for more accurate results.
     98      *
     99      * @param ppm400 The measured reference voltage at 400 ppm
    100      * @param ppm40000 The measured reference voltage at 1000 ppm
    101      */
    102     void setCalibration(float ppm400, float ppm1000);
    103 
    104     /**
    105      * Returns the voltage detected on the analog pin
    106      *
    107      * @return The detected voltage
    108      */
    109     float volts();
    110 
    111     /**
    112      * Returns the computed CO2 concentration in ppm (Parts Per
    113      * Million).  This method will return 0.0 if the reference voltage
    114      * is greater than the ppm400 value.  Essentially, ppm values
    115      * below 400 will be reported as 0.
    116      *
    117      * @return The computed CO2 concentration in ppm
    118      */
    119     float ppm();
    120 
    121     /**
    122      * Read the digital pin and return true if the set threshold has
    123      * been reached or exceeded.  This threshold is set by adjusting
    124      * the potentiometer on the sensor.
    125      *
    126      * @return true if the threshold has been reached, false otherwise
    127      */
    128     bool thresholdReached();
    129 
    130   protected:
    131     mraa::Aio m_aio;
    132     mraa::Gpio m_gpio;
    133 
    134     // calibration values
    135     float m_zeroPointValue;
    136     float m_reactionValue;
    137 
    138     // ADC resolution
    139     int m_aRes;
    140 
    141   private:
    142     float m_aref;
    143   };
    144 }
    145 
    146 
    147