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237 lines
9.1 KiB
Markdown
237 lines
9.1 KiB
Markdown
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[](https://github.com/marketplace/actions/arduino_ci)
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[](https://github.com/RobTillaart/MTP40C/actions/workflows/jsoncheck.yml)
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[](https://github.com/RobTillaart/MTP40C/actions/workflows/arduino-lint.yml)
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[](https://github.com/RobTillaart/MTP40C/blob/master/LICENSE)
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[](https://github.com/RobTillaart/MTP40C/releases)
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# MTP40C / MTP40D
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Arduino library for MTP40C and MTP40D CO2 sensor.
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(include image)
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## Description
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The library for the MTP40C / MTP40D CO2 sensor is experimental as not all functionality is tested.
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Both the MTP40C and MTP40D sensor is an NDIR (Non Dispersive InfraRed) CO2 sensor.
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The sensor communicates over a 19200 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 MTP40D 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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### Hardware interface
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#### MTP40-C
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```
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TOPVIEW MTP40-C
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+-------------+---+
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| | O |
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Vin 1 --| +---+
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GND 2 --| |
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TX 3 --| |
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RX 4 --| |
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NC 5 --| +---+
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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 | TX | Transmit 19200 baud |
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| 4 | RX | Receive 19200 baud |
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| 5 | NC | Not Connected |
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#### MTP40-D
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```
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TOPVIEW MTP40-D
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+-------------+
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VCC 5 --| |-- 1 Vin
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TX 6 --| |-- 2 GND
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RX 7 --| |-- 3 ALARM
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NC 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 2000 PPM, LOW below 1800 PPM (hysteresis) |
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| 4 | PWM/I2C | PWM out or I2C select |
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| 5 | VCC_O | 3V3 out for serial |
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| 6 | TX | Transmit 19200 baud or SDA |
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| 7 | RX | Receive 19200 baud or SCL |
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| 8 | NC | Not Connected |
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| 9 | GND | idem |
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## Interface
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### Warnings
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During tests with an UNO the communication over Software Serial did fail sometimes.
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Therefore it is important to **always check return values** 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()**. By having a delay(100) between the calls
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everything ran far more stable (within my test). Todo seek optimum delay(), added in Future section below.
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The CRC of the sensor responses are not verified by the library.
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### Constructors
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- **MTP40(Stream \* str)** constructor. should get a Serial port as parameter e.g. \&Serial, \&Serial1. This is the base class.
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- **MTP40C(Stream \* str)** constructor. should get a Serial port as parameter e.g. \&Serial, \&Serial1
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or a software Serial port. That Serial port must connect to the sensor.
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- **MTP40D(Stream \* str)** constructor. should get a Serial port as parameter e.g. \&Serial, \&Serial1
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or a software Serial port. That Serial port must connect to the sensor.
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- **bool begin(uint8_t address = 0x64)** initialize the device.
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Sets the address to communicate to the sensor. Address values allowed 0 .. 247.
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Uses the factory default value of 0x64 when no parameter is given.
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Also resets internal settings.
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- **bool isConnected()** returns true if the address as set by **begin()**
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or the default address of 0x64 (decimal 100) can be found on the Serial 'bus'.
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- **uint8_t getType()** returns 2 for the MTP40C and 3 for the MTP40D sensor.
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Return 255 for the MTP40 base class.
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### CO2 Measurement
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- **uint16_t getGasConcentration()** returns the CO2 concentration in PPM (parts per million).
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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 error value with
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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 MTP40_OK;
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### Configuration
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- **uint8_t getAddress()** request the address from the device.
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Expect a value from 0 .. 247.
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Returns **MTP40_INVALID_ADDRESS** (0xFF) if the request fails.
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- **bool setAddress(uint8_t address = 0x64)** set a new address for the device.
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0x64 as default. Returns false if not successful.
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If **setSpecificAddress()** is called, this specific address will be used for further commands.
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These address functions are only needed if handling multiple devices. (to be tested)
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- **void setGenericAddress()** uses the broadcast address 0xFE in all requests.
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This is the default behaviour of the library.
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- **void setSpecificAddress()** uses the address specified in **begin()** or
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**setAddress()** or the default 0x64 in all requests.
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- **bool useSpecificAddress()** returns true if the specific address is used.
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Returns false if the generic / broadcast address is used.
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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 long enough
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for even the longest command. This timeout is needed if the sensor did not read the
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command correctly, preventing the host to wait indefinitely.
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- **void setTimeout(uint32_t to = 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 the process of calibration.
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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 **MTP40_INVALID_AIR_PRESSURE** in case request fails.
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Default is 1013.0.
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- **bool setAirPressureReference(float apr)** to calibrate the air pressure.
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One can calibrate the sensor with an external device.
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Value for air pressure should between 700.0 and 1100.0.
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The function returns **false** if the parameter is out of range or if the request fails.
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#### SPC calibration
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This 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(float spc)** takes several minutes. see datasheet.
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spc should be between 400 and 5000.
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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 SPC is finished or not. The call also fails if the request fails.
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As far as known the SPC point 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 a longer period
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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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- **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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**WARNING**: in our test the values in the datasheet seems to be not in sync with the sensor used.
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The function returned **0x00 for CLOSED and 0xFF for OPEN**.
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- **bool setSelfCalibrationHours(uint16_t hrs)** Sets the number of hours between self calibration
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moments. Valid values are 24 - 720 .
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- **uint16_t getSelfCalibrationHours()** returns the value set above.
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## Operations
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See examples.
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## Future
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#### CRC
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- CRC in PROGMEM
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- CRC test responses sensor
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#### Performance
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- performance measurements
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- optimize performance if possible
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- caching? what?
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- seek optimum delay() between calls.
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- investigate wire length
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#### Other
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- serial bus with multiple devices? => diodes
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- improve readability code (e.g. parameter names)
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- move all code from .h to .cpp file
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## Sponsor
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The development of this MTP40C library is sponsored by [TinyTronics, Netherlands](https://www.tinytronics.nl/shop/nl).
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