Since | Origin / Contributor | Maintainer | Source |
---|---|---|---|
2016-02-21 | vsky279 | vsky279 | bit.c |
This module provides a simple interface to BME280/BMP280 temperature/air presssure/humidity sensors (Bosch Sensortec).
Note that you must call init()
before you can start reading values!
For given air pressure and sea level air pressure returns the altitude in meters as an integer multiplied with 100, i.e. altimeter function.
bme280.altitude(P, QNH)
P
measured pressureQNH
current sea level pressurealtitude in meters of measurement point
Reads the sensor and returns the air temperature in hectopascals as an integer multiplied with 1000 or nil
when readout is not successful.
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.
bme280.baro()
none
P
air pressure in hectopascals multiplied by 1000T
temperature in celsius as an integer multiplied with 100For given temperature and relative humidity returns the dew point in celsius as an integer multiplied with 100.
bme280.dewpoint(H, T)
H
relative humidity in percent multiplied by 1000.T
temperate in celsius multiplied by 100.dew point in celsisus
Reads the sensor and returns the air relative humidity in percents as an integer multiplied with 100 or nil
when readout is not successful.
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.
bme280.humi()
none
H
last relative humidity reading in % times 1000T
temperature in celsius as an integer multiplied with 100Initializes module. Initialization is mandatory before read values.
bme280.init(sda, scl, [temp_oss, press_oss, humi_oss, power_mode, inactive_duration, IIR_filter])
sda
- SDA pinscl
- SCL pintemp_oss
- Controls oversampling of temperature data. Default oversampling is 16x.press_oss
- Controls oversampling of pressure data. Default oversampling is 16x.humi_oss
- Controls oversampling of humidity data. Default oversampling is 16xsensor_mode
- Controls the sensor mode of the device. Default sensor more is normal.inactive_duration
- Controls inactive duration in normal mode. Default inactive duration is 20ms.IIR_filter
- Controls the time constant of the IIR filter. Default fitler coefficient is 16.temp_oss , press_oss , humi_oss |
Data oversampling |
---|---|
0 | Skipped (output set to 0x80000) |
1 | oversampling ×1 |
2 | oversampling ×2 |
3 | oversampling ×4 |
4 | oversampling ×8 |
5 | oversampling ×16 |
sensor_mode |
Sensor mode |
---|---|
0 | Sleep mode |
1 and 2 | Forced mode |
3 | Normal mode |
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.
inactive_duration |
t standby (ms) |
---|---|
0 | 0.5 |
1 | 62.5 |
2 | 125 |
3 | 250 |
4 | 500 |
5 | 1000 |
6 | 10 |
7 | 20 |
IIR_filter |
Filter coefficient |
---|---|
0 | Filter off |
1 | 2 |
2 | 4 |
3 | 8 |
4 | 16 |
nil
if initialization has failed (no sensor connected?), 2
if sensor is BME280, 1
if sensor is BMP280
alt=320 -- altitude of the measurement place
bme280.init(3, 4)
P, T = bme280.baro()
print(string.format("QFE=%d.%03d", P/1000, P%1000))
-- convert measure air pressure to sea level pressure
QNH = bme280.qfe2qnh(P, alt)
print(string.format("QNH=%d.%03d", QNH/1000, QNH%1000))
H, T = bme280.humi()
print(string.format("T=%d.%02d", T/100, T%100))
print(string.format("humidity=%d.%03d%%", H/1000, H%1000))
D = bme280.dewpoint(H, T)
print(string.format("dew_point=%d.%02d", D/100, D%100))
-- altimeter function - calculate altitude based on current sea level pressure (QNH) and measure pressure
P = bme280.baro()
curAlt = bme280.altitude(P, QNH)
print(string.format("altitude=%d.%02d", curAlt/100, curAlt%100))
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.
Example of readout in forced mode (asynchronous)
bme280.init(3, 4, nil, nil, nil, 0) -- initialize to sleep mode
bme280.startreadout(0, function ()
T = bme280.temp()
print(string.format("T=%d.%02d", T/100, T%100))
end)
For given altitude converts the air pressure to sea level air pressure.
bme280.qfe2qnh(P, altitude)
P
measured pressurealtitude
altitude in meters of measurement pointsea level pressure
Starts readout (turns the sensor into forced mode). After the readout the sensor turns to sleep mode.
bme280.startreadout(delay, callback)
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.callback
if provided it will be invoked after given delay
. The sensor reading should be finalized by then so.nil
Reads the sensor and returns the temperature in celsius as an integer multiplied with 100.
bme280.temp()
none
T
temperature in celsius as an integer multiplied with 100 or nil
when readout is not successfult_fine
temperature measure used in pressure and humidity compensation formulas (generally no need to use this value)