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242 lines
8.8 KiB
Markdown
242 lines
8.8 KiB
Markdown
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[](https://github.com/marketplace/actions/arduino_ci)
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[](https://github.com/RobTillaart/MTP40F/actions/workflows/arduino-lint.yml)
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[](https://github.com/RobTillaart/MTP40F/actions/workflows/jsoncheck.yml)
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[](https://github.com/RobTillaart/MTP40F/issues)
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[](https://github.com/RobTillaart/MTP40F/blob/master/LICENSE)
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[](https://github.com/RobTillaart/MTP40F/releases)
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[](https://registry.platformio.org/libraries/robtillaart/MTP40F)
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# MTP40F
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Arduino library for MTP40F CO2 sensor.
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## Description
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The library for the MTP40F CO2 sensor is **experimental** as not all functionality is tested.
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It is based upon my https://github.com/RobTillaart/MTP40C library.
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The MTP40F sensor is an NDIR (Non Dispersive InfraRed) CO2 sensor.
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It returns the CO2 level in PPM = parts per million, and in normal
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outside air it should be between 400 - 420.
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The sensor communicates over a 9600 baud serial (TTL) interface with a microprocessor or PC.
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This implies that calls which can take up to 25 bytes can take as much as about 20 milliseconds.
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On the other hand this low baud rate implies it will work over relative long distances.
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This signal quality over longer distances is not investigated.
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The MTP40F has more interface options, I2C, PWM and ALARM.
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This library does not support these other interfaces for now.
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However minimal examples are added to have a starter but these
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need to be tested if and how well these work.
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#### Warnings
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During tests with an UNO the communication over Software Serial did
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fail a few times.
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Therefore it is important to **always check return values**
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to make your project more robust.
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During tests it became clear that the sensor needs time to process
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commands e.g. **setSelfCalibration()**.
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The CRC of the sensor responses are not verified by the library (yet).
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#### Hardware interface MTP40-F
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Has TTL level RS232, I2C and PWM IO.
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```
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TOPVIEW MTP40-F
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+-------------+
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VCC (3v3 out) 5 --| |-- 1 Vin
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TX / SDA 6 --| |-- 2 GND
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RX / SCL 7 --| |-- 3 ALARM
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R/T 8 --| |-- 4 PWM / I2C
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GND 9 --| |
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+-------------+
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```
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| Pin | Name | Description |
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|:-----:|:-----------|:-----------------------------|
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| 1 | Vin | 4.2V - 5.5V |
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| 2 | GND | idem |
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| 3 | ALARM | HIGH above 1000 PPM, LOW below 800 PPM (hysteresis) |
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| 4 | PWM/I2C | PWM out |
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| 5 | VCC_O | 3V3 out for serial |
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| 6 | TX / SDA | Transmit 9600 baud or SDA |
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| 7 | RX / SCL | Receive 9600 baud or SCL |
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| 8 | R/T | select Serial or I2C |
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| 9 | GND | idem |
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#### Links
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- https://www.co2.earth/ - current outdoor CO2 level can be used for calibrating.
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- https://keelingcurve.ucsd.edu/ - historical outdoor CO2 level.
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- https://github.com/RobTillaart/MTP40C
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- https://github.com/RobTillaart/MHZCO2
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- https://github.com/RobTillaart/Cozir
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## Interface
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```cpp
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#include "MTP40F.h"
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```
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#### Constructor
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- **MTP40F(Stream \* str)** constructor. Should get a Serial port as parameter
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e.g. \&Serial, \&Serial1 or a software Serial port.
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That Serial port must connect to the sensor, check datasheet for pins.
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- **bool begin()** initialize the internal settings for the device.
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- **uint8_t getType()** returns type, see below.
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Return 255 for the MTP40 base class.
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| Type | Model | Notes |
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|:------:|:--------:|:--------:|
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| 2 | MTP40C | for ref only
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| 3 | MTP40D | for ref only
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| 5 | MTP40F |
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| 255 | MTP40 | for ref only
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#### CO2 Measurement
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- **uint16_t getGasConcentration()** returns the CO2 concentration in PPM.
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The function returns **MTP40_INVALID_GAS_LEVEL** if the request fails.
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- **void suppressError(bool se)** sets or clears a flag that replaces the
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error value with the last read value if the request fails.
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This is useful when plotting the values and one do not want a sudden spike.
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One can still check **lastError()** to see if the value was OK.
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- **bool getSuppressError()** gets the value of the suppress flag.
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- **int lastError()** returns last error set by **getGasConcentration()**
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or by **getAirPressureReference()**
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Reading resets internal error to MTP40F_OK;
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#### Timeout communication
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The library can set a maximum timeout in the communication with the sensor.
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Normally this is not needed to set as the default of 100 milliseconds is
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long enough for even the longest command.
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This timeout is needed if the sensor did not process the command correctly,
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preventing the host to wait indefinitely.
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- **void setTimeout(uint32_t timeOut = 100)** sets the timeout.
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If no parameter is given a default timeout of 100 milliseconds is set.
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- **uint32_t getTimeout()** get the value set above or the default.
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Value returned is time in milliseconds.
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## Calibration
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Please read datasheet before using these functions to understand
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the process of calibration.
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Note the outdoor calibration CO2 level differs per day and one should
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check a local airport or weather station for a good reference.
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The University of San Diego keeps track of CO2 for a long time now.
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See - https://keelingcurve.ucsd.edu/
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#### Air pressure calibration
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- **float getAirPressureReference()** returns the air pressure reference from the device.
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Returns **MTP40F_INVALID_AIR_PRESSURE** in case request fails.
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Default is 1013 (note no decimals) == 1 ATM.
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- **bool setAirPressureReference(float apr = 1013)** to calibrate the air pressure.
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Default value = 1013 hPa (1 Atm).
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One can calibrate the sensor with an external device.
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Value for air pressure should normally between 700 and 1100.
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The function returns false if the parameter is out of range or if the request fails.
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For pressure conversion - https://github.com/RobTillaart/pressure
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#### SinglePointCorrection calibration
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It takes a relative short time (few minutes) to calibrate the sensor in a known
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gas concentration.
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- **bool setSinglePointCorrection(uint32_t spc)** takes several minutes. See datasheet.
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The parameter **spc** should be between 400 and 2000 (assumption).
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The function returns false if the parameter is out of range or if the request fails.
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- **bool getSinglePointCorrectionReady()** To see if setting the **SPC** has
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finished or not.
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The call also fails if the request fails.
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As far as known the **SPC** value can not be retrieved from the sensor.
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#### Self calibration
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Self calibration is a process in which the sensor takes the minimum values over
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a longer period between 24 - 720 hours as the reference for minimum outdoor values.
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Note that 720 hours is 30 days / 1 month.
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Default seems to be 168 hours == 1 week.
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- **bool openSelfCalibration()** start the self calibration cycle.
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- **bool closeSelfCalibration()** stop the self calibration cycle.
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- **uint8_t getSelfCalibrationStatus()** Returns if the selfCalibration is open or closed.
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The function returned 0x00 for CLOSED and 0xFF for OPEN.
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- **bool setSelfCalibrationHours(uint16_t hours = 168)** Sets the number of hours
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between self calibration moments.
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Valid values for hours are 24 - 720 (1 day up to 1 month).
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Default value = 168 hours = 1 week.
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- **uint16_t getSelfCalibrationHours()** returns the value set above.
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Note: read datasheet!
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## Future
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#### Must
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- update documentation
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- reorder
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#### Should
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- **setSinglePointCorrection(spc)** investigate parameter.
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datasheet states 0x2000 but that is 8192 which is rather strange.
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Assumption 2000 decimal is meant.
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#### Could
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- serial bus with multiple devices? => diodes
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- separate document
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- move all code from .h to .cpp file
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- reuse command buffer as return buffer?
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- saves a bit.
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- **getAirPressureReference()** could be smarter
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- always same value
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- from cache
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- dirty flag (-1);
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- ERROR handling.
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- some functions returning bool should return int
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to handle errors better MTP40F_OK or ERROR flag.
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#### Wont
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- store SPC point in the class?
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## Support
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If you appreciate my libraries, you can support the development and maintenance.
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Improve the quality of the libraries by providing issues and Pull Requests, or
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donate through PayPal or GitHub sponsors.
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Thank you,
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