MG811 Class Reference

API for the DFRobot CO2 Sensor. More...

Detailed Description

• ID: mg811
• Name: CO2 Sensor
• Other Names: MG811
• Category: gaseous
• Manufacturer: dfrobot
• Link: http://www.dfrobot.com/index.php?route=product/product&product_id=1023
• Connection: analog

This sensor returns an an analog voltage that falls as the concentration of CO2 increases. It contains a heater that must be allowed to 'warm' up the sensor before measurements are stable (hours to days is the recommendation). It requires that the MCU be powered from an external power supply (not USB) at 5v, since the heater will consume significant current.

The sensor should be allowed to 'heat' up for some time before beginning use, typically a couple of hours minimum. It also needs fairly precise calibration at 400ppm and 1000ppm to return meaningful results.

The sensor also incorporates a potentiometer that can be adjusted to specific threshold. Once that threshold is reached, an LED on the sensor will light, and the digital pin will be driven high.

    // Instantiate an MG811 on analog pin A0, and digital pin D2 with an
    // analog reference voltage of MG811_AREF (5.0)
    upm::MG811 sensor(0, 2, MG811_AREF);

    // Every tenth of a second, sample the sensor and output it's
    // detected CO2 concentration in parts per million (ppm)

    while (shouldRun) {
        cout << "CO2 concentration in PPM: " << sensor.ppm() << endl;

        upm_delay_us(100000);
    }

Public Member Functions
	MG811 (int pin, int dpin, float aref=5.0)
	~MG811 ()
float	getReferenceVoltage ()
void	setCalibration (float ppm400, float ppm1000)
float	volts ()
float	ppm ()
bool	thresholdReached ()

Protected Attributes
mraa::Aio	m_aio
mraa::Gpio	m_gpio
float	m_zeroPointValue
float	m_reactionValue
int	m_aRes

Constructor & Destructor Documentation

MG811	(	int	pin,
		int	dpin,
		float	aref = 5.0
	)

MG811 constructor

Parameters

pin	Analog pin to use
dpin	Digital pin that indicates threshold
aref	Analog reference voltage; default is 5.0 V

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~MG811

(

)

MG811 destructor

Member Function Documentation

float getReferenceVoltage

(

)

Return a cumputed reference voltage to be used in calibration.

Returns

Computed reference voltage

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void setCalibration	(	float	ppm400,
		float	ppm1000
	)

Set calibration parameters. You should measure the reference voltage you get when at CO2 concentrations of 400ppm (ambient) and 1000ppm using the getReferenceVoltage() method. Then specify those voltages here for more accurate results.

Parameters

ppm400	The measured reference voltage at 400 ppm
ppm1000	The measured reference voltage at 1000 ppm

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float volts

(

)

Returns the voltage detected on the analog pin

Returns

The detected voltage

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float ppm

(

)

Returns the computed CO2 concentration in ppm (Parts Per Million). This method will return 0.0 if the reference voltage is greater than the ppm400 value. Essentially, ppm values below 400 will be reported as 0.

Returns

The computed CO2 concentration in ppm

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bool thresholdReached

(

)

Read the digital pin and return true if the set threshold has been reached or exceeded. This threshold is set by adjusting the potentiometer on the sensor.

Returns

true if the threshold has been reached, false otherwise

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The documentation for this class was generated from the following files:

• src/mg811/mg811.hpp
• src/mg811/mg811.cxx