199 lines
6.6 KiB
Markdown
199 lines
6.6 KiB
Markdown
# BME280 module
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| Since | Origin / Contributor | Maintainer | Source |
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| :----- | :-------------------- | :---------- | :------ |
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| 2016-02-21 | [vsky279](https://github.com/vsky279) | [vsky279](https://github.com/vsky279) | [bit.c](../../../app/modules/bme280.c)|
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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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Note that you must call [`init()`](#bme280init) before you can start reading values!
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## bme280.altitude()
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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.altitude(P, QNH)`
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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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altitude in meters of measurement point
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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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|0|Skipped (output set to 0x80000)|
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|1|oversampling ×1|
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|2|oversampling ×2|
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|3|oversampling ×4|
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|4|oversampling ×8|
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|**5**|**oversampling ×16**|
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|`sensor_mode`|Sensor mode|
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|-----|-----------------|
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|0|Sleep mode|
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|1 and 2|Forced mode|
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|**3**|**Normal mode**|
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Using forced mode is recommended for applications which require low sampling rate or hostbased synchronization. The sensor enters into sleep mode after a forced readout. Please refer to BME280 Final Datasheet for more details.
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|`inactive_duration`|t standby (ms)|
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|-----|-----------------|
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|0|0.5|
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|1|62.5|
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|2|125|
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|3|250|
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|4|500|
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|5|1000|
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|6|10|
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|**7**|**20**|
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|`IIR_filter`|Filter coefficient |
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|-----|-----------------|
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|0|Filter off|
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|1|2|
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|2|4|
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|3|8|
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|**4**|**16**|
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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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```lua
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alt=320 -- altitude of the measurement place
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bme280.init(3, 4)
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P, T = bme280.baro()
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print(string.format("QFE=%d.%03d", P/1000, P%1000))
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-- convert measure air pressure to sea level pressure
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QNH = bme280.qfe2qnh(P, alt)
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print(string.format("QNH=%d.%03d", QNH/1000, QNH%1000))
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H, T = bme280.humi()
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print(string.format("T=%d.%02d", T/100, T%100))
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print(string.format("humidity=%d.%03d%%", H/1000, H%1000))
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D = bme280.dewpoint(H, T)
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print(string.format("dew_point=%d.%02d", D/100, D%100))
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-- altimeter function - calculate altitude based on current sea level pressure (QNH) and measure pressure
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P = bme280.baro()
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curAlt = bme280.altitude(P, QNH)
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print(string.format("altitude=%d.%02d", curAlt/100, curAlt%100))
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```
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Use `bme280.init(sda, scl, 1, 3, 0, 3, 0, 4)` for "game mode" - Oversampling settings pressure ×4, temperature ×1, humidity ×0, sensor mode: normal mode, inactive duration = 0.5 ms, IIR filter settings filter coefficient 16.
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Example of readout in forced mode (asynchronous)
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```lua
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bme280.init(3, 4, nil, nil, nil, 0) -- initialize to sleep mode
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bme280.startreadout(0, function ()
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T = bme280.temp()
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print(string.format("T=%d.%02d", T/100, T%100))
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end)
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```
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## bme280.qfe2qnh()
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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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`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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#### Returns
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sea level pressure
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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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#### Syntax
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`bme280.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](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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#### Returns
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`nil`
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## bme280.temp()
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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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`bme280.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) |