MQ-7 gas sensor, typically used for detecting carbon monoxide. More...

#include <MQ7.h>

Inheritance diagram for RumPi::MQ7:

Collaboration diagram for RumPi::MQ7:

Public Member Functions
	MQ7 ()
	Builds a default MQ-7 (carbon monoxide) sensor and initializes its datasheet values. More...

	MQ7 (IAnalogDigitalConverterComponent *analogToDigitalConverter, const unsigned int &analogToDigitalConverterIndex, const unsigned int &digitalOutputPinNumber)
	Builds an MQ-7 that reads through an ADC and also exposes a digital threshold pin. More...

	MQ7 (IAnalogDigitalConverterComponent *analogToDigitalConverter, const unsigned int &analogToDigitalConverterIndex)
	Builds an analog-only MQ-7 that reads through an ADC. More...

	MQ7 (const unsigned int &digitalOutputPinNumber)
	Builds a digital-only MQ-7 that reports only its threshold-output pin. More...

virtual	~MQ7 ()
	Destroys the sensor, turning it off first. More...

void	Initialize () override
	Initializes the MQ-7's datasheet values (its carbon monoxide gas curve) and precomputes a PPM value for every possible raw analog reading, since the PPM formula is expensive but the mapping never changes. More...

double	ReadGasValue () const override
	Reads the current carbon monoxide PPM for the sensor's raw reading (from the precomputed cache). More...

double	CalculateCarbonMonoxidePPM (const double &sensorGasValueInVolts) const
	Computes the carbon monoxide concentration (PPM) from the sensor's output voltage using an exponential fit of the sensor's response curve. More...

std::string	ToString () const override
	Serializes the MQ-7's gas name, raw reading, and carbon monoxide PPM to a string. More...

Public Member Functions inherited from RumPi::GasSensor
virtual void	CalculateInitialR0 ()
	Calibrates the sensor: computes and stores its clean-air resistance (R0). More...

	GasSensor ()
	Builds a default gas sensor with zeroed calibration values and no ADC or digital pin. More...

	GasSensor (IAnalogDigitalConverterComponent *analogToDigitalConverter, const EComponentType &gasSensorType, const unsigned int &analogToDigitalConverterIndex, const unsigned int &digitalOutputPinNumber)
	Builds an analog gas sensor that reads through an ADC and also exposes a digital threshold pin. More...

	GasSensor (IAnalogDigitalConverterComponent *analogToDigitalConverter, const EComponentType &gasSensorType, const unsigned int &analogToDigitalConverterIndex)
	Builds an analog-only gas sensor that reads through an ADC (no digital threshold pin). More...

	GasSensor (const EComponentType &gasSensorType, const unsigned int &digitalOutputPinNumber)
	Builds a digital-only gas sensor that reports only its threshold-output pin (no ADC). More...

virtual	~GasSensor ()
	Destroys the gas sensor, turning it off first. More...

virtual void	TurnOn ()
	Turns the sensor on. More...

virtual void	TurnOff ()
	Turns the sensor off. More...

virtual void	Initialize ()
	Initializes the sensor's datasheet values. More...

int	ReadRawAnalogValue () const
	Reads the raw analog value from the sensor's ADC channel. More...

int	ReadDigitalValue ()
	Reads the sensor's digital threshold-output pin (1 when the configured gas threshold is exceeded). More...

virtual double	ReadGasValue () const
	Gets the most recently processed gas value. More...

virtual void	ProcessRawValues () override
	Reads the sensor and computes the current gas value (PPM) from the RS/R0 ratio using the datasheet's log-log curve. More...

virtual std::string	ToString () const override
	Serializes the sensor's current gas value (PPM), a rough percentage, and the raw reading to a string. More...

unsigned int	GetAnalogToDigitalConverterIndex () const
	Gets the ADC channel index this sensor reads from. More...

unsigned int	GetDigitalOutputPinNumber () const
	Gets the digital threshold-output pin (UINT_MAX if unused). More...

double	GetInitialValueR0 () const
	Gets the sensor's clean-air resistance (R0) from calibration. More...

double	GetResistorValueRL () const
	Gets the load resistor value (RL) from the sensor's datasheet. More...

double	GetCurrentValueRS () const
	Gets the sensor's current resistance (RS). More...

const char *	GetDetectibleConcentration () const
	Gets a human-readable detectable-concentration range for this sensor. More...

EComponentType	GetGasSensorType () const
	Gets this sensor's component type (which MQ sensor it is). More...

const char *	GetGasSensorTypeAsString () const
	Gets this sensor's type as a display string (e.g. More...

const char *	GetGasSensorTypeAsString (const EComponentType &gasSensorType) const
	Maps a gas-sensor component type to its display string (e.g. More...

IAnalogDigitalConverterComponent *	GetAnalogDigitalConverter () const
	Gets the ADC this sensor reads its analog value through. More...

const GasData &	GetGasData () const
	Gets the per-gas curve data (slope/intercept and concentration points) for this sensor. More...

Public Member Functions inherited from RumPi::BaseComponent
	BaseComponent ()
	Builds a base component with an unknown type and an empty name. More...

virtual	~BaseComponent ()
	Virtual destructor so deleting a component through a BaseComponent* also cleans up the concrete subclass. More...

virtual void	TurnOn ()=0
	Turns the component on (e.g. More...

virtual void	TurnOff ()=0
	Turns the component off. More...

virtual std::string	ToString () const =0
	Serializes the component's current readings to a string (usually JSON). More...

virtual void	ProcessRawValues ()=0
	Reads and processes the component's latest raw values (called once per poll). More...

virtual EComponentType	GetComponentType () const
	Gets the component's type. More...

const std::string &	GetName () const
	Gets the component's unique per-instance name. More...

void	SetName (const std::string &name)
	Sets the component's unique per-instance name. More...

Additional Inherited Members
Static Public Member Functions inherited from RumPi::BaseComponent
static std::string	ComponentTypeToString (const EComponentType theComponentTypeToConvert)
	Maps an EComponentType to its string name. More...

static EComponentType	StringToComponentType (const std::string &theComponentTypeName)
	Maps a type name back to its EComponentType (the inverse of ComponentTypeToString), so the client can turn the type carried on the wire back into a value it can look an icon up with. More...

Static Public Attributes inherited from RumPi::GasSensor
static constexpr double	GAS_SENSOR_VOLTAGE = 5.0
	The supply voltage the gas sensor runs on. More...

static const int	CALIBRATION_SAMPLE_TIMES = 200
	The number of samples taken during the calibration phase. More...

static const int	CALIBRATION_SAMPLE_INTERVAL = 250
	Milliseconds between samples during the calibration phase. More...

static const int	READ_SAMPLE_INTERVAL = 250
	Milliseconds between samples during normal operation. More...

Protected Member Functions inherited from RumPi::GasSensor
virtual double	CalculateR0 ()
	Samples the sensor many times in clean air, averages the reading, converts it to resistance (RS), and divides by the clean-air factor to get R0. More...

virtual double	CalculateRS (const double &sensorValueInVolts) const
	Computes the sensor's resistance (RS) from its output voltage, using the load resistor RL and supply voltage. More...

virtual double	CalculateRSR0Ratio (const double &sensorValueInVolts) const
	Computes the RS/R0 ratio (used to look up PPM on the datasheet curve) from the sensor's output voltage. More...

double	ConvertRawSensorValueToVolts (const double &rawGasSensorValue) const
	Converts a raw analog reading to its equivalent voltage (using the sensor's supply voltage and the ADC's maximum value). More...

double	ConvertVoltsToRawSensorValue (const double &volts) const
	Converts a voltage back to its equivalent raw analog value (the inverse of ConvertRawSensorValueToVolts). More...

double	GetAnalogToDigitalConverterMaxRawValue () const
	Gets the ADC's full-scale raw count for scaling raw readings to volts (PCF8591 = 255 8-bit, MCP3008 = 1023 10-bit), falling back to the 10-bit convention when no ADC is wired. More...

double	GetAnalogToDigitalConverterVoltage () const
	Gets the ADC's reference voltage for scaling raw readings to volts (defined by the wired ADC, e.g. More...

Protected Attributes inherited from RumPi::GasSensor
unsigned int	myAnalogToDigitalConverterIndex
	The ADC channel index this sensor reads its analog value from. More...

unsigned int	myDigitalOutputPinNumber
	The digital output (threshold) pin, or UINT_MAX if unused. More...

double	myInitialValueR0
	The sensor's resistance in clean air (R0), from calibration. More...

double	myResistorValueRL
	The load resistor value (RL) from the sensor's datasheet. More...

double	myCurrentValueRS
	The sensor's current resistance (RS). More...

double	myCleanAirFactor
	The clean-air factor (RS/R0 in clean air) from the datasheet. More...

double	myRawGasSensorValue
	The most recent raw analog reading. More...

double	myCurrentGasValue
	The most recent computed gas value (PPM). More...

const char *	myDetectibleConcentration
	A human-readable detectable-concentration range for this sensor. More...

IAnalogDigitalConverterComponent *	myAnalogToDigitalConverter
	The ADC this sensor reads its analog value through. More...

GasData	myGasData
	Per-gas curve data (slope/intercept) used to convert the RS/R0 ratio to PPM. More...

Protected Attributes inherited from RumPi::BaseComponent
EComponentType	myComponentType
	The kind of component this is (set by each concrete subclass). More...

std::string	myName
	A unique per-instance name, assigned when the component is added to the manager. More...

Detailed Description

MQ-7 gas sensor, typically used for detecting carbon monoxide.

Author: Eddie O'Hagan

Date: 8/13/2026

Constructor & Destructor Documentation

◆ MQ7() [1/4]

RumPi::MQ7::MQ7 ( )

Builds a default MQ-7 (carbon monoxide) sensor and initializes its datasheet values.

Author: Eddie O'Hagan

Date: 8/13/2026

MQ7 carbonMonoxideSensor;

RumPi::MQ7::MQ7

MQ7()

Builds a default MQ-7 (carbon monoxide) sensor and initializes its datasheet values.

Definition: MQ7.cpp:15

◆ MQ7() [2/4]

RumPi::MQ7::MQ7	(	IAnalogDigitalConverterComponent *	analogToDigitalConverter,
		const unsigned int &	analogToDigitalConverterIndex,
		const unsigned int &	digitalOutputPinNumber
	)

Builds an MQ-7 that reads through an ADC and also exposes a digital threshold pin.

Author: Eddie O'Hagan

Date: 8/13/2026

MQ7 carbonMonoxideSensor(adc, 5, PIN_GPIO_27);

RumPi::PIN_GPIO_27

constexpr unsigned int PIN_GPIO_27

BCM GPIO pin 27.

Definition: Common.h:53

Parameters

[in]	analogToDigitalConverter	The ADC the sensor reads through.
[in]	analogToDigitalConverterIndex	The ADC channel index.
[in]	digitalOutputPinNumber	The digital threshold-output pin.

◆ MQ7() [3/4]

RumPi::MQ7::MQ7	(	IAnalogDigitalConverterComponent *	analogToDigitalConverter,
		const unsigned int &	analogToDigitalConverterIndex
	)

Builds an analog-only MQ-7 that reads through an ADC.

Author: Eddie O'Hagan

Date: 8/13/2026

MQ7 carbonMonoxideSensor(adc, 5);

Parameters

[in]	analogToDigitalConverter	The ADC the sensor reads through.
[in]	analogToDigitalConverterIndex	The ADC channel index.

◆ MQ7() [4/4]

RumPi::MQ7::MQ7 ( const unsigned int & digitalOutputPinNumber )

Builds a digital-only MQ-7 that reports only its threshold-output pin.

Author: Eddie O'Hagan

Date: 8/13/2026

MQ7 carbonMonoxideSensor(PIN_GPIO_27);

Parameters

[in] digitalOutputPinNumber The digital threshold-output pin.

◆ ~MQ7()

RumPi::MQ7::~MQ7 ( )

virtual

Destroys the sensor, turning it off first.

Author: Eddie O'Hagan

Date: 8/13/2026

MQ7* sensor = new MQ7();

delete sensor;

Member Function Documentation

◆ CalculateCarbonMonoxidePPM()

double RumPi::MQ7::CalculateCarbonMonoxidePPM ( const double & sensorGasValueInVolts ) const

Computes the carbon monoxide concentration (PPM) from the sensor's output voltage using an exponential fit of the sensor's response curve.

Author: Eddie O'Hagan

Date: 8/13/2026

double ppm = carbonMonoxideSensor.CalculateCarbonMonoxidePPM(sensorGasValueInVolts);

Parameters

[in] sensorGasValueInVolts The sensor's output voltage.

Returns: The carbon monoxide concentration, in PPM.

◆ Initialize()

void RumPi::MQ7::Initialize ( )

overridevirtual

Initializes the MQ-7's datasheet values (its carbon monoxide gas curve) and precomputes a PPM value for every possible raw analog reading, since the PPM formula is expensive but the mapping never changes.

Author: Eddie O'Hagan

Date: 8/13/2026

//Called by every MQ7 constructor.

Reimplemented from RumPi::GasSensor.

◆ ReadGasValue()

double RumPi::MQ7::ReadGasValue ( ) const

overridevirtual

Reads the current carbon monoxide PPM for the sensor's raw reading (from the precomputed cache).

Author: Eddie O'Hagan

Date: 8/13/2026

double ppm = carbonMonoxideSensor.ReadGasValue();

Returns: The current carbon monoxide concentration, in PPM.

Reimplemented from RumPi::GasSensor.

◆ ToString()

std::string RumPi::MQ7::ToString ( ) const

overridevirtual

Serializes the MQ-7's gas name, raw reading, and carbon monoxide PPM to a string.

Author: Eddie O'Hagan

Date: 8/13/2026

std::string data = carbonMonoxideSensor.ToString();

Returns: A multi-line string describing the sensor's reading.

Reimplemented from RumPi::GasSensor.

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

Source/Headers/RumPi/Components/MQ7.h
Source/Implementations/RumPi/Components/MQ7.cpp

Public Member Functions

Additional Inherited Members

Detailed Description

Constructor & Destructor Documentation

◆ MQ7() [1/4]

◆ MQ7() [2/4]

◆ MQ7() [3/4]

◆ MQ7() [4/4]

◆ ~MQ7()

Member Function Documentation

◆ CalculateCarbonMonoxidePPM()

◆ Initialize()

◆ ReadGasValue()

◆ ToString()