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267 lines
11 KiB
Markdown
267 lines
11 KiB
Markdown
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[](https://github.com/marketplace/actions/arduino_ci)
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[](https://github.com/RobTillaart/AGS02MA/actions/workflows/arduino-lint.yml)
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[](https://github.com/RobTillaart/AGS02MA/actions/workflows/jsoncheck.yml)
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[](https://github.com/RobTillaart/AGS02MA/blob/master/LICENSE)
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[](https://github.com/RobTillaart/AGS02MA/releases)
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# AGS02MA
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Arduino library for AGS02MA TVOC sensor.
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This library is still experimental, so please use with care.
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Note the warning about the I2C low speed, the device works at max 30 KHz.
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Since 0.3.1 this library uses 25 KHz.
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## I2C
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### PIN layout from left to right
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| Front L->R | Description |
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|:----------:|:------------|
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| pin 1 | VDD + |
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| pin 2 | SDA data |
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| pin 3 | GND |
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| pin 4 | SCL clock |
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### WARNING - LOW SPEED
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The sensor uses I2C at very low speed <= 30 KHz.
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For an Arduino UNO the lowest speed supported is about 30.4KHz (TWBR = 255) which works.
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First runs with Arduino UNO indicate 2 failed reads in > 500 Reads, so less than 1%
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Tests with ESP32 / ESP8266 at 30 KHz look good,
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tests with ESP32 at lower clock speeds are to be done but expected to work.
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The library sets the clock speed to 30 KHz (for non AVR) during operation
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and resets it default to 100 KHz after operation.
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This is done to minimize interference with the communication of other devices.
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The reset clock speed can be changed with **setI2CResetSpeed(speed)** e.g. to 200 or 400 KHz.
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#### 0.3.1 fix.
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Version 0.3.1 sets the **I2C prescaler TWSR** register of the Arduino UNO to 4 so the lowest
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speed possible is reduced to about 8 KHz.
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A test run 4 hours with 6000++ reads on an UNO at 25 KHz gave 0 errors.
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So the communication speed will be set to 25 KHz, also for other boards, for stability.
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After communication the clock (+ prescaler) is reset again as before.
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## Version 118 problems
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The library can request the version with **getSensorVersion()**.
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My devices all report version 117 and this version is used to develop / test this library.
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There are devices reported with version 118 which behave differently.
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### ugM3 not supported
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See - https://github.com/RobTillaart/AGS02MA/issues/11
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The version 118 seems only to support the **PPB** and not the **ugM3** mode.
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It is unclear if this is an incident, bug or a structural change in the firmware.
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If you encounter similar problems with setting the mode (any version), please let me know.
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That will help indicating if this is a "structural change" or incident.
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### Calibrate problem!
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See - https://github.com/RobTillaart/AGS02MA/issues/13
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In this issue a problem is reported with a version 118 sensor.
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The problem exposed itself after running the calibration sketch (command).
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The problem has been confirmed by a 2nd version 118 sensor.
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Additional calibration runs did not fix the problem.
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Version 117 seem to have no problems with calibration.
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**Advice**: do **NOT** calibrate a version 118.
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Note: the version 0.2.0 determines the version in the calibration function so
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it won't calibrate any non 117 version.
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### Please report your experiences.
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If you have a AGS20MA device, version 117 or 118 or other,
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please let me know your experiences
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with the sensor and this (or other) library.
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## Interface
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### Constructor
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- **AGS02MA(uint8_t deviceAddress = 26, TwoWire \*wire = &Wire)** constructor, with default address and default I2C interface.
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- **bool begin(uint8_t sda, uint8_t scl)** begin for ESP32 and ESP8266.
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- **bool begin()** initializer for Arduino UNO a.o.
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- **bool isConnected()** returns true if device address can be seen on I2C.
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- **void reset()** reset internal variables.
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### Timing
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- **bool isHeated()** returns true if 2 minutes have passed after startup (call of **begin()** ).
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Otherwise the device is not optimal ready.
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According to the datasheet the preheating will improve the quality of the measurements.
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- **uint32_t lastRead()** last time the device is read, timestamp is in milliseconds since start.
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Returns 0 if **readPPB()** or **readUGM3()** is not called yet.
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This function allows to implement sort of asynchronous wait.
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One must keep reads at least 1.5 seconds but preferred 3 seconds apart according to the datasheet.
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### Administration
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- **bool setAddress(const uint8_t deviceAddress)** sets a new address for the sensor.
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If function succeeds the address changes immediately and will be persistent over a reboot.
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- **uint8_t getAddress()** returns the set address. Default the function will return 26 or 0x1A.
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- **uint8_t getSensorVersion()** reads sensor version from device.
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If the version cannot be read the function will return 255.
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(My test sensors all return version 117, version 118 is reported)
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- **uint32_t getSensorDate()** (experimental) reads bytes from the sensor that seem to indicate the production date(?). This date is encoded in an uint32_t to minimize footprint as it is a debug function.
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```cpp
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uint32_t dd = sensor.getSensorDate();
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Serial.println(dd, HEX); // prints YYYYMMDD e.g. 20210203
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```
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### I2C clock speed
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The library sets the clock speed to 25 KHz during operation
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and resets it to 100 KHz after operation.
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This is done to minimize interference with the communication of other devices.
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The following function can change the I2C reset speed to e.g. 200 or 400 KHz.
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- **void setI2CResetSpeed(uint32_t speed)** sets the I2C speed the library need to reset the I2C speed to.
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- **uint32_t getI2CResetSpeed()** returns the value set. Default is 100 KHz.
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### setMode
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The default mode at startup of the sensor is PPB = parts per billion.
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- **bool setPPBMode()** sets device in PartPerBillion mode. Returns true on success.
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- **bool setUGM3Mode()** sets device in micro gram per cubic meter mode. Returns true on success.
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- **uint8_t getMode()** returns mode set. 0 = PPB, 1 = UGm3, 255 = not set.
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#### PPB versus UGM3
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There is no 1 to 1 relation between the PPB and the uG/m3 readings as this relation depends
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on the weight of the individual molecules.
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PPB is therefore an more an absolute indicator where uG/m3 is sort of relative indicator.
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If the gas is unknown, PPB is in my opinion the preferred measurement.
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From an unverified source the following formula:
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M = molecular weight of the gas.
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**μg/m3 = (ppb)\*(12.187)\*(M) / (273.15 + °C)**
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Simplified formula for 1 atm @ 25°C:
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**μg/m3 = ppb \* M \* 0.04087539829 μg/m3**
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Some known gasses
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| gas | Common name | ratio ppb-μg/m3 | molecular weight M |
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|:-----|:------------------|:--------------------|:------------------:|
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| SO2 | Sulphur dioxide | 1 ppb = 2.62 μg/m3 | 64 gr/mol |
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| NO2 | Nitrogen dioxide | 1 ppb = 1.88 μg/m3 | 46 gr/mol |
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| NO | Nitrogen monoxide | 1 ppb = 1.25 μg/m3 | 30 gr/mol |
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| O3 | Ozone | 1 ppb = 2.00 μg/m3 | 48 gr/mol |
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| CO | Carbon Monoxide | 1 ppb = 1.145 μg/m3 | 28 gr/mol |
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| C6H6 | Benzene | 1 ppb = 3.19 μg/m3 | 78 gr/mol |
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### Read the sensor
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WARNING: The datasheet advises to take 3 seconds between reads.
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Tests gave stable results at 1.5 second intervals.
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Use this faster rate at your own risk.
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- **uint32_t readPPB()** reads PPB (parts per billion) from device.
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Typical value should be between 1 .. 999999.
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Returns **lastPPB()** value if failed so one does not get sudden jumps in graphs.
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Check **lastStatus()** and **lastError()** to get more info about success.
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Time needed is ~35 milliseconds.
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- **uint32_t readUGM3()** reads UGM3 (microgram per cubic meter) current value from device.
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Typical values depend on the molecular weight of the TVOC.
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Returns **lastUGM3()** if failed so one does not get sudden jumps in graphs.
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- **float readPPM()** returns parts per million (PPM).
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This function is a wrapper around readPPB().
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Typical value should be between 0.01 .. 999.99
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- **float readMGM3()** returns milligram per cubic meter.
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- **float readUGF3()** returns microgram per cubic feet.
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### Error Codes
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| ERROR_CODES | value |
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|:---------------------------|:-----:|
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| AGS02MA_OK | 0 |
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| AGS02MA_ERROR | -10 |
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| AGS02MA_ERROR_CRC | -11 |
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| AGS02MA_ERROR_READ | -12 |
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| AGS02MA_ERROR_NOT_READY | -13 |
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#### Cached values
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- **float lastPPM()** returns last readPPM (parts per million) value (cached).
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- **uint32_t lastPPB()** returns last read PPB (parts per billion) value (cached). Should be between 1..999999.
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- **uint32_t lastUGM3()** returns last read UGM3 (microgram per cubic meter) value (cached).
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### Calibration
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- **bool zeroCalibration()** to be called after at least 5 minutes in fresh air.
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See example sketch.
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- **bool manualZeroCalibration(uint16_t value = 0)** Set the zero calibration value manually.
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To be called after at least 5 minutes in fresh air.
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- For v117: 0-65535 = automatic calibration.
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- For v118: 0 = automatic calibration, 1-65535 manual calibration.
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- **bool getZeroCalibrationData(ZeroCalibrationData &data)** fills a data struct with the current zero calibration status and value.
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Returns true on success.
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### Other
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- **bool readRegister(uint8_t address, RegisterData ®)** fills a data struct with the chip's register data at that address.
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Primarily intended for troubleshooting and analysis of the sensor. Not recommended to build applications on top of this method's raw data.
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Returns true when the struct is filled, false when the data could not be read.
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Note: unlike other public methods, CRC errors don't return false or show up in `lastError()`, instead the CRC result is stored in `RegisterData.crcValid`.
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- **int lastError()** returns last error.
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- **uint8_t lastStatus()** returns status byte from last read.
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Read datasheet or table below for details. A new read is needed to update this.
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- **uint8_t dataReady()** returns RDY bit from last read.
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#### Status bits.
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| bit | description | notes |
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|:-----:|:------------------------------------|:--------|
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| 7-4 | internal use |
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| 3-1 | 000 = PPB 001 = uG/M3 |
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| 0 | RDY bit 0 = ready 1 = not ready | 1 == busy
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## Future
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- test test test ...
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- improve documentation
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- add indicative table for PPB health zone
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- check the mode bits of the status byte with internal \_mode.
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- elaborate error handling.
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- create an async interface for **readPPB()** if possible
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- put the I2C speed code in 2 inline functions
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- less repeating conditional code places
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- setLowSpeed() + setNormalSpeed()
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