mirror of
https://github.com/RobTillaart/Arduino.git
synced 2024-10-03 18:09:02 -04:00
236 lines
9.1 KiB
Markdown
236 lines
9.1 KiB
Markdown
|
|
[](https://github.com/marketplace/actions/arduino_ci)
|
|
[](https://github.com/RobTillaart/MTP40C/actions/workflows/jsoncheck.yml)
|
|
[](https://github.com/RobTillaart/MTP40C/actions/workflows/arduino-lint.yml)
|
|
[](https://github.com/RobTillaart/MTP40C/blob/master/LICENSE)
|
|
[](https://github.com/RobTillaart/MTP40C/releases)
|
|
|
|
|
|
# MTP40C / MTP40D
|
|
|
|
Arduino library for MTP40C and MTP40D CO2 sensor.
|
|
|
|
(include image)
|
|
|
|
|
|
## Description
|
|
|
|
The library for the MTP40C / MTP40D CO2 sensor is experimental as not all functionality is tested.
|
|
|
|
Both the MTP40C and MTP40D sensor is an NDIR (Non Dispersive InfraRed) CO2 sensor.
|
|
|
|
The sensor communicates over a 19200 baud serial (TTL) interface with a microprocessor or PC.
|
|
This implies that calls which can take up to 25 bytes can take as much as about 20 milliseconds.
|
|
|
|
On the other hand this low baud rate implies it will work over relative long distances.
|
|
This signal quality over longer distances is not investigated.
|
|
|
|
The MTP40D has more interface options, I2C, PWM and ALARM.
|
|
This library does not support these other interfaces for now.
|
|
However minimal examples are added to have a starter but these
|
|
need to be tested if and how well these work.
|
|
|
|
|
|
### Hardware interface
|
|
|
|
|
|
#### MTP40-C
|
|
|
|
```
|
|
TOPVIEW MTP40-C
|
|
+-------------+---+
|
|
| | O |
|
|
Vin 1 --| +---+
|
|
GND 2 --| |
|
|
TX 3 --| |
|
|
RX 4 --| |
|
|
NC 5 --| +---+
|
|
| | O |
|
|
+-------------+---+
|
|
```
|
|
|
|
| Pin | Name | Description |
|
|
|:----:|:------|:--------------------|
|
|
| 1 | Vin | 4.2V--5.5V |
|
|
| 2 | GND | idem |
|
|
| 3 | TX | Transmit 19200 baud |
|
|
| 4 | RX | Receive 19200 baud |
|
|
| 5 | NC | Not Connected |
|
|
|
|
|
|
#### MTP40-D
|
|
|
|
```
|
|
TOPVIEW MTP40-D
|
|
+-------------+
|
|
| |
|
|
VCC 5 --| |-- 1 Vin
|
|
TX 6 --| |-- 2 GND
|
|
RX 7 --| |-- 3 ALARM
|
|
NC 8 --| |-- 4 PWM / I2C
|
|
GND 9 --| |
|
|
| |
|
|
+-------------+
|
|
```
|
|
|
|
| Pin | Name | Description |
|
|
|:----:|:--------|:----------------------------|
|
|
| 1 | Vin | 4.2V--5.5V |
|
|
| 2 | GND | idem |
|
|
| 3 | ALARM | HIGH above 2000 PPM, LOW below 1800 PPM (hysteresis) |
|
|
| 4 | PWM/I2C | PWM out or I2C select |
|
|
| 5 | VCC_O | 3V3 out for serial |
|
|
| 6 | TX | Transmit 19200 baud or SDA |
|
|
| 7 | RX | Receive 19200 baud or SCL |
|
|
| 8 | NC | Not Connected |
|
|
| 9 | GND | idem |
|
|
|
|
|
|
## Interface
|
|
|
|
### Warnings
|
|
|
|
During tests with an UNO the communication over Software Serial did fail sometimes.
|
|
Therefore it is important to **always check return values** to make your project more robust.
|
|
|
|
During tests it became clear that the sensor needs time to process
|
|
commands e.g. **setSelfCalibration()**. By having a delay(100) between the calls
|
|
everything ran far more stable (within my test). Todo seek optimum delay(), added in Future section below.
|
|
|
|
The CRC of the sensor responses are not verified by the library.
|
|
|
|
|
|
### Constructors
|
|
|
|
- **MTP40(Stream \* str)** constructor. should get a Serial port as parameter e.g. \&Serial, \&Serial1. This is the base class.
|
|
- **MTP40C(Stream \* str)** constructor. should get a Serial port as parameter e.g. \&Serial, \&Serial1
|
|
or a software Serial port. That Serial port must connect to the sensor.
|
|
- **MTP40D(Stream \* str)** constructor. should get a Serial port as parameter e.g. \&Serial, \&Serial1
|
|
or a software Serial port. That Serial port must connect to the sensor.
|
|
- **bool begin(uint8_t address = 0x64)** initialize the device.
|
|
Sets the address to communicate to the sensor. Address values allowed 0 .. 247.
|
|
Uses the factory default value of 0x64 when no parameter is given.
|
|
Also resets internal settings.
|
|
- **bool isConnected()** returns true if the address as set by **begin()**
|
|
or the default address of 0x64 (decimal 100) can be found on the Serial 'bus'.
|
|
- **uint8_t getType()** returns 2 for the MTP40C and 3 for the MTP40D sensor.
|
|
Return 255 for the MTP40 base class.
|
|
|
|
|
|
### CO2 Measurement
|
|
|
|
- **uint16_t getGasConcentration()** returns the CO2 concentration in PPM (parts per million).
|
|
The function returns **MTP40_INVALID_GAS_LEVEL** if the request fails.
|
|
|
|
- **void suppressError(bool se)** sets or clears a flag that replaces the error value with
|
|
the last read value if the request fails.
|
|
This is useful when plotting the values and one do not want a sudden spike.
|
|
One can still check **lastError()** to see if the value was OK.
|
|
- **bool getSuppressError()** gets the value of the suppress flag.
|
|
- **int lastError()** returns last error set by **getGasConcentration()**
|
|
or by **getAirPressureReference()**
|
|
Reading resets internal error to MTP40_OK;
|
|
|
|
|
|
### Configuration
|
|
|
|
- **uint8_t getAddress()** request the address from the device.
|
|
Expect a value from 0 .. 247.
|
|
Returns **MTP40_INVALID_ADDRESS** (0xFF) if the request fails.
|
|
- **bool setAddress(uint8_t address = 0x64)** set a new address for the device.
|
|
0x64 as default. Returns false if not successful.
|
|
If **setSpecificAddress()** is called, this specific address will be used for further commands.
|
|
|
|
These address functions are only needed if handling multiple devices. (to be tested)
|
|
- **void setGenericAddress()** uses the broadcast address 0xFE in all requests.
|
|
This is the default behaviour of the library.
|
|
- **void setSpecificAddress()** uses the address specified in **begin()** or
|
|
**setAddress()** or the default 0x64 in all requests.
|
|
- **bool useSpecificAddress()** returns true if the specific address is used.
|
|
Returns false if the generic / broadcast address is used.
|
|
|
|
The library can set a maximum timeout in the communication with the sensor.
|
|
Normally this is not needed to set as the default of 100 milliseconds is long enough
|
|
for even the longest command. This timeout is needed if the sensor did not read the
|
|
command correctly, preventing the host to wait indefinitely.
|
|
- **void setTimeout(uint32_t to = 100)** sets the timeout.
|
|
If no parameter is given a default timeout of 100 milliseconds is set.
|
|
- **uint32_t getTimeout()** get the value set above or the default.
|
|
Value returned is time in milliseconds.
|
|
|
|
|
|
### Calibration
|
|
|
|
Please read datasheet before using these functions to understand the process of calibration.
|
|
|
|
|
|
#### Air pressure calibration
|
|
|
|
- **float getAirPressureReference()** returns the air pressure reference from the device.
|
|
Returns **MTP40_INVALID_AIR_PRESSURE** in case request fails.
|
|
Default is 1013.0.
|
|
- **bool setAirPressureReference(float apr)** to calibrate the air pressure.
|
|
One can calibrate the sensor with an external device.
|
|
Value for air pressure should between 700.0 and 1100.0.
|
|
The function returns **false** if the parameter is out of range or if the request fails.
|
|
|
|
|
|
#### SPC calibration
|
|
|
|
This takes a relative short time (few minutes) to calibrate the sensor in a known
|
|
gas concentration.
|
|
|
|
- **bool setSinglePointCorrection(float spc)** takes several minutes. see datasheet.
|
|
spc should be between 400 and 5000.
|
|
The function returns **false** if the parameter is out of range or if the request fails.
|
|
- **bool getSinglePointCorrectionReady()** To see if SPC is finished or not. The call also fails if the request fails.
|
|
|
|
As far as known the SPC point can not be retrieved from the sensor.
|
|
|
|
|
|
#### Self calibration
|
|
|
|
Self calibration is a process in which the sensor takes the minimum values over a longer period
|
|
between 24 - 720 hours as the reference for minimum outdoor values.
|
|
Note that 720 hours is 30 days / 1 month.
|
|
|
|
- **bool openSelfCalibration()** start the self calibration cycle.
|
|
- **bool closeSelfCalibration()** stop the self calibration cycle.
|
|
- **uint8_t getSelfCalibrationStatus()** Returns if the selfCalibration is open or closed.
|
|
**WARNING**: in our test the values in the datasheet seems to be not in sync with the sensor used.
|
|
The function returned **0x00 for CLOSED and 0xFF for OPEN**.
|
|
- **bool setSelfCalibrationHours(uint16_t hrs)** Sets the number of hours between self calibration
|
|
moments. Valid values are 24 - 720 .
|
|
- **uint16_t getSelfCalibrationHours()** returns the value set above.
|
|
|
|
|
|
## Future
|
|
|
|
#### CRC
|
|
|
|
- CRC in PROGMEM
|
|
- CRC test responses sensor
|
|
|
|
#### Performance
|
|
|
|
- performance measurements
|
|
- optimize performance if possible
|
|
- caching? what?
|
|
- seek optimum delay() between calls.
|
|
- investigate wire length
|
|
|
|
#### Other
|
|
|
|
- serial bus with multiple devices? => diodes
|
|
- improve readability code (e.g. parameter names)
|
|
|
|
|
|
## Operations
|
|
|
|
See examples.
|
|
|
|
|
|
## Sponsor
|
|
|
|
The development of this MTP40C library is sponsored by [TinyTronics, Netherlands](https://www.tinytronics.nl/shop/nl).
|