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/*
* Author: Jon Trulson <jtrulson@ics.com>
* Copyright (c) 2015 Intel Corporation.
*
* Thanks to public domain code by Martin Liddament for some useful clues!
* http://www.veetech.org.uk/CO2_Monitor_Sketch_2_Operation.txt
* and sandbox electronics (http://sandboxelectronics.com/?p=147).
*
* 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.
*/
#include <iostream>
#include <math.h>
#include "mg811.hpp"
using namespace std;
using namespace upm;
// voltage gain of the DC amplifier
static const float dcGain = 8.5;
MG811::MG811(int pin, int dpin, float aref) :
m_aio(pin), m_gpio(dpin)
{
m_aRes = m_aio.getBit();
m_aref = aref;
m_gpio.dir(mraa::DIR_IN);
// these are just placeholder values (coarsely measured during
// development), you should determine the appropriate values (in
// volts) for your environment at the specified concentrations. Use
// the getReferenceVoltage() method to get these values at 400ppm
// and 1000ppm respectively. Good luck.
setCalibration(0.5514, 0.370);
}
MG811::~MG811()
{
}
float MG811::volts()
{
int val = m_aio.read();
return(float(val) * (m_aref / float(1 << m_aRes)));
}
void MG811::setCalibration(float ppm400, float ppm1000)
{
m_zeroPointValue = ppm400;
m_reactionValue = ppm1000;
}
float MG811::getReferenceVoltage()
{
return (volts() / dcGain);
}
float MG811::ppm()
{
static const float log400 = log10f(400);
static const float log1000 = log10f(1000);
float val = volts();
if ((val / dcGain) >= m_zeroPointValue)
return 0.0;
else
return powf(10.0, ((val/dcGain)-m_zeroPointValue) /
(m_reactionValue / (log400-log1000))+log400);
}
bool MG811::thresholdReached()
{
return (m_gpio.read() ? true : false);
}
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