Rework the BME280 docs to be in line with our standards
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Marcel Stör
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# bme280 module
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# BME280 module
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The bme280 module provides simple interface to BME280/BMP280 temperature/air presssure/humidity sensor.
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This module provides a simple interface to [BME280/BMP280 temperature/air presssure/humidity sensors](http://www.bosch-sensortec.com/bst/products/all_products/bme280) (Bosch Sensortec).
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|Method|Description|
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|---------------|-------------|
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|[init()](#init)|Initializes the module and sets the pin configuration.|
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|[temp()](#temp)|Reads the sensor and returns the temperature in celsius as an integer multiplied with 100.|
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|[baro()](#baro)|Reads the sensor and returns the air temperature in hectopascals as an integer multiplied with 1000.|
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|[humi()](#humi)|Reads the sensor and returns the air relative humidity in percents as an integer multiplied with 100.|
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|[startreadout()](#startreadout)|Starts readout (turns the sensor into forced mode).|
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|[qfe2qnh()](#qfe2qnh)|For given altitude converts the air pressure to sea level air pressure.|
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|[altitude()](#altitude)|For given air pressure and sea level air pressure returns the altitude in meters as an integer multiplied with 100.|
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|[dewpoint()](#dewpoint)|For given temperature and relative humidity returns the dew point in celsius as an integer multiplied with 100.|
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Note that you must call [`init()`](#bme280init) before you can start reading values!
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## Methods
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## bme280.altitude()
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###init()
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For given air pressure and sea level air pressure returns the altitude in meters as an integer multiplied with 100, i.e. altimeter function.
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####Description
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Initialize module. Initialization is mandatory before read values.
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#### Syntax
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`bme280.altitude(P, QNH)`
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####Syntax
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`init(sda, scl)`
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#### Parameters
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- `P` measured pressure
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- `QNH` current sea level pressure
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`init(sda, scl, temp_oss, press_oss, humi_oss, power_mode, inactive_duration, IIR_filter)`
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#### Returns
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altitude in meters of measurement point
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####Parameters
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* `sda` - SDA pin
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* `scl` - SCL pin
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* (optional) `temp_oss` - Controls oversampling of temperature data. Default oversampling is 16x.
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* (optional) `press_oss` - Controls oversampling of pressure data. Default oversampling is 16x.
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* (optional) `humi_oss` - Controls oversampling of humidity data. Default oversampling is 16x
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* (optional) `sensor_mode` - Controls the sensor mode of the device. Default sensor more is normal.
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* (optional) `inactive_duration` - Controls inactive duration in normal mode. Default inactive duration is 20ms.
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* (optional) `IIR_filter` - Controls the time constant of the IIR filter. Default fitler coefficient is 16.
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## bme280.baro()
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Reads the sensor and returns the air temperature in hectopascals as an integer multiplied with 1000 or `nil` when readout is not successful.
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Current temperature is needed to calculate the air pressure so temperature reading is performed prior reading pressure data. Second returned variable is therefore current temperature.
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#### Syntax
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`bme280.baro()`
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#### Parameters
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none
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#### Returns
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- `P` air pressure in hectopascals multiplied by 1000
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- `T` temperature in celsius as an integer multiplied with 100
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## bme280.dewpoint()
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For given temperature and relative humidity returns the dew point in celsius as an integer multiplied with 100.
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#### Syntax
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`bme280.dewpoint(H, T)`
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#### Parameters
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- `H` relative humidity in percent multiplied by 1000.
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- `T` temperate in celsius multiplied by 100.
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#### Returns
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dew point in celsisus
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## bme280.humi()
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Reads the sensor and returns the air relative humidity in percents as an integer multiplied with 100 or `nil` when readout is not successful.
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Current temperature is needed to calculate the relative humidity so temperature reading is performed prior reading pressure data. Second returned variable is therefore current temperature.
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#### Syntax
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`bme280.humi()`
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#### Parameters
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none
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#### Returns
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- `H` last relative humidity reading in % times 1000
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- `T` temperature in celsius as an integer multiplied with 100
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## bme280.init()
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Initializes module. Initialization is mandatory before read values.
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#### Syntax
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`bme280.init(sda, scl, [temp_oss, press_oss, humi_oss, power_mode, inactive_duration, IIR_filter])`
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#### Parameters
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- `sda` - SDA pin
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- `scl` - SCL pin
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- (optional) `temp_oss` - Controls oversampling of temperature data. Default oversampling is 16x.
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- (optional) `press_oss` - Controls oversampling of pressure data. Default oversampling is 16x.
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- (optional) `humi_oss` - Controls oversampling of humidity data. Default oversampling is 16x
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- (optional) `sensor_mode` - Controls the sensor mode of the device. Default sensor more is normal.
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- (optional) `inactive_duration` - Controls inactive duration in normal mode. Default inactive duration is 20ms.
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- (optional) `IIR_filter` - Controls the time constant of the IIR filter. Default fitler coefficient is 16.
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|`temp_oss`, `press_oss`, `humi_oss`|Data oversampling|
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|-----|-----------------|
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@ -71,10 +116,10 @@ Using forced mode is recommended for applications which require low sampling rat
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|3|8|
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|**4**|**16**|
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####Returns
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`nil` initialization has failed (no sensor connected?), `2` sensor is BME280, `1` sensor is BMP280
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#### Returns
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`nil` if initialization has failed (no sensor connected?), `2` if sensor is BME280, `1` if sensor is BMP280
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### Example
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#### Example
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```lua
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alt=320 -- altitude of the measurement place
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@ -109,117 +154,43 @@ bme280.startreadout(0, function ()
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end)
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```
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**-** [Back to index](#index)
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## bme280.qfe2qnh()
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###temp()
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####Description
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Reads the sensor and returns the temperature in celsius as an integer multiplied with 100.
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####Syntax
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`temp()`
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####Parameters
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none
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####Returns
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* `T` - temperature in celsius as an integer multiplied with 100 or `nil` when readout is not successful.
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* `t_fine` - temperature measure used in pressure and humidity compensation formulas (generally no need to use this value)
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**-** [Back to index](#index)
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###baro()
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####Description
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Reads the sensor and returns the air temperature in hectopascals as an integer multiplied with 1000 or `nil` when readout is not successful.
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Current temperature is needed to calculate the air pressure so temperature reading is performed prior reading pressure data. Second returned variable is therefore current temperature.
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####Syntax
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`baro()`
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####Parameters
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none
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####Returns
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* `P` - air pressure in hectopascals multiplied by 1000.
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* `T` - temperature in celsius as an integer multiplied with 100.
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**-** [Back to index](#index)
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###humi()
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####Description
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Reads the sensor and returns the air relative humidity in percents as an integer multiplied with 100 or `nil` when readout is not successful.
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Current temperature is needed to calculate the relative humidity so temperature reading is performed prior reading pressure data. Second returned variable is therefore current temperature.
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####Syntax
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`humi()`
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####Parameters
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none
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####Returns
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* `H` - last relative humidity reading in % times 1000.
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* `T` - temperature in celsius as an integer multiplied with 100.
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**-** [Back to index](#index)
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###startreadout()
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Starts readout (turns the sensor into forced mode). After the readout the sensor turns to sleep mode.
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####Syntax
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`startreadout(delay, callback)`
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####Parameters
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* `delay` - sets sensor to forced mode and calls the `callback` (if provided) after given number of milliseconds. For 0 the default delay is set to 113ms (sufficient time to perform reading for oversampling settings 16x). For different oversampling setting please refer to BME280 Final Datasheet - Appendix B: Measurement time and current calculation.
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* `callback` - if provided it will be invoked after given `delay`. The sensor reading should be finalized by then so.
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####Returns
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`nil`
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**-** [Back to index](#index)
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###qfe2qnh()
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Description
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For given altitude converts the air pressure to sea level air pressure.
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####Syntax
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`qfe2qnh(P, altitude)`
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#### Syntax
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`bme280.qfe2qnh(P, altitude)`
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####Parameters
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* `P` - measured pressure
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* `altitude` - altitude in meters of measurement point
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#### Parameters
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- `P` measured pressure
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- `altitude` altitude in meters of measurement point
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####Returns
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* `QNH` - sea level pressure
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#### Returns
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sea level pressure
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**-** [Back to index](#index)
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## bme280.startreadout()
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Starts readout (turns the sensor into forced mode). After the readout the sensor turns to sleep mode.
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###altitude()
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####Description
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For given air pressure and sea level air pressure returns the altitude in meters as an integer multiplied with 100, i.e. altimeter function.
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#### Syntax
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`bme280.startreadout(delay, callback)`
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####Syntax
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`altitude(P, QNH)`
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#### Parameters
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- `delay` sets sensor to forced mode and calls the `callback` (if provided) after given number of milliseconds. For 0 the default delay is set to 113ms (sufficient time to perform reading for oversampling settings 16x). For different oversampling setting please refer to [BME280 Final Datasheet - Appendix B: Measurement time and current calculation](http://ae-bst.resource.bosch.com/media/_tech/media/datasheets/BST-BME280_DS001-11.pdf#page=51).
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- `callback` if provided it will be invoked after given `delay`. The sensor reading should be finalized by then so.
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####Parameters
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* `P` - measured pressure
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* `QNH` - current sea level pressure
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#### Returns
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`nil`
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####Returns
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* `altitude` - altitude in meters of measurement point
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## bme280.temp()
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**-** [Back to index](#index)
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Reads the sensor and returns the temperature in celsius as an integer multiplied with 100.
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###dewpoint()
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####Description
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For given temperature and relative humidity returns the dew point in celsius as an integer multiplied with 100.
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#### Syntax
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`bme280.temp()`
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####Syntax
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`dewpoint(H, T)`
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#### Parameters
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none
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####Parameters
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* `H` - relative humidity in percent multiplied by 1000.
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* `T` - temperate in celsius multiplied by 100.
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####Returns
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* `dewpoint` - dew point in celsisus.
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**-** [Back to index](#index)
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#### Returns
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- `T` temperature in celsius as an integer multiplied with 100 or `nil` when readout is not successful
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- `t_fine` temperature measure used in pressure and humidity compensation formulas (generally no need to use this value)
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