60cfe88e37
This driver was developed on a DFRobot CO2 sensor based on the MG811: http://www.dfrobot.com/index.php?route=product/product&product_id=1023 It seems to *require* very precise calibration at 400ppm and 1000ppm to be accurate. It also gets pretty hot (due to the heater) and consumes significant current. Signed-off-by: Jon Trulson <jtrulson@ics.com> Signed-off-by: sisinty sasmita patra <sisinty.s.patra@intel.com>
95 lines
2.7 KiB
C++
95 lines
2.7 KiB
C++
/*
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* Author: Jon Trulson <jtrulson@ics.com>
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* Copyright (c) 2015 Intel Corporation.
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*
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* Thanks to public domain code by Martin Liddament for some useful clues!
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* http://www.veetech.org.uk/CO2_Monitor_Sketch_2_Operation.txt
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* and sandbox electronics (http://sandboxelectronics.com/?p=147).
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*
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* Permission is hereby granted, free of charge, to any person obtaining
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* a copy of this software and associated documentation files (the
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* "Software"), to deal in the Software without restriction, including
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* without limitation the rights to use, copy, modify, merge, publish,
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* distribute, sublicense, and/or sell copies of the Software, and to
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* permit persons to whom the Software is furnished to do so, subject to
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* the following conditions:
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*
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* The above copyright notice and this permission notice shall be
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* included in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
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* LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
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* OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
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* WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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*/
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#include <iostream>
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#include <math.h>
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#include "mg811.h"
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using namespace std;
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using namespace upm;
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// voltage gain of the DC amplifier
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static const float dcGain = 8.5;
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MG811::MG811(int pin, int dpin, float aref) :
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m_aio(pin), m_gpio(dpin)
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{
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m_aRes = m_aio.getBit();
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m_aref = aref;
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m_gpio.dir(mraa::DIR_IN);
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// these are just placeholder values (coarsely measured during
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// development), you should determine the appropriate values (in
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// volts) for your environment at the specified concentrations. Use
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// the getReferenceVoltage() method to get these values at 400ppm
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// and 1000ppm respectively. Good luck.
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setCalibration(0.5514, 0.370);
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}
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MG811::~MG811()
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{
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}
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float MG811::volts()
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{
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int val = m_aio.read();
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return(float(val) * (m_aref / float(1 << m_aRes)));
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}
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void MG811::setCalibration(float ppm400, float ppm1000)
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{
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m_zeroPointValue = ppm400;
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m_reactionValue = ppm1000;
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}
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float MG811::getReferenceVoltage()
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{
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return (volts() / dcGain);
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}
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float MG811::ppm()
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{
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static const float log400 = log10f(400);
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static const float log1000 = log10f(1000);
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float val = volts();
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if ((val / dcGain) >= m_zeroPointValue)
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return 0.0;
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else
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return powf(10.0, ((val/dcGain)-m_zeroPointValue) /
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(m_reactionValue / (log400-log1000))+log400);
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}
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bool MG811::thresholdReached()
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{
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return (m_gpio.read() ? true : false);
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}
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