1 /*
2  * Author: Jon Trulson <jtrulson@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