Since | Origin / Contributor | Maintainer | Source |
---|---|---|---|
2016-02-21 | vsky279 | vsky279 | bme280_math.c |
This module provides calculation routines for BME280/BMP280 temperature/air presssure/humidity sensors (Bosch Sensortec). Communication with the sensor is ensured by Lua code through I2C or SPI interface. Read registers are passed to the module to calculate measured values.
See bme280 Lua module for examples.
For given air pressure (called QFE in aviation - see wiki QNH article) and sea level air pressure returns the altitude in meters, i.e. altimeter function.
bme280_math.altitude([self], P, QNH)
self
userdata or table structure so that the function can be directly called as object method, parameter is ignored in the calculationP
measured pressureQNH
current sea level pressurealtitude in meters of measurement point
For given temperature and relative humidity returns the dew point in celsius.
bme280_math.dewpoint([self], H, T)
self
userdata or table structure so that the function can be directly called as object method, parameter is ignored in the calculationH
relative humidity in percent (100 means 100%)T
temperate in celsiusdew point in celsisus
For given altitude converts the air pressure to sea level air pressure (QNH).
bme280_math.qfe2qnh([self], P, altitude)
self
userdata or table structure so that the function can be directly called as object method, parameter is ignored in the calculationP
measured pressurealtitude
altitude in meters of measurement pointsea level pressure
Reads the sensor and returns the temperature, the air pressure, the air relative humidity and see level air pressure when altitude
is specified.
bme280_math.read(bme280sensor, registers, [altitude])
bme280sensor
- BME280 sensor user data returned by bme280_math.setup()
registers
- string of 8 bytes (chars) registers read from BME280_REGISTER_PRESS
altitude
- altitude in meters of measurement point. If provided also the air pressure converted to sea level air pressure is returned.T
temperature in celsiusP
air pressure in hectopascalsH
relative humidity in percentQNH
air pressure in hectopascalsReturns nil
if the conversion is not successful.
Initializes module. Initialization is mandatory before read values.
bme280_math.setup(registers, [temp_oss, press_oss, humi_oss, power_mode, inactive_duration, IIR_filter])
BME280_REGISTER_DIG_T
, 18 bytes (chars) BME280_REGISTER_DIG_P
and optional (not present for BMP280 sensor) 8 bytes (chars) of BME280_REGISTER_DIG_H1
(1 byte) and BME280_REGISTER_DIG_H2
(7 bytes)temp_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 filter 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 |
bme280sensor
user data (nil
if initialization has failed)config
3 (2 for BME280) field table with configuration parameters to be written to registers BME280_REGISTER_CONFIG
, BME280_REGISTER_CONTROL_HUM
, BME280_REGISTER_CONTROL
consecutivelySee bme280 Lua module documentation.
name | address |
---|---|
BME280_REGISTER_CONTROL | 0xF4 |
BME280_REGISTER_CONTROL_HUM | 0xF2 |
BME280_REGISTER_CONFIG | 0xF5 |
BME280_REGISTER_CHIPID | 0xD0 |
BME280_REGISTER_DIG_T | 0x88 (0x88-0x8D (6)) |
BME280_REGISTER_DIG_P | 0x8E (0x8E-0x9F (18)) |
BME280_REGISTER_DIG_H1 | 0xA1 |
BME280_REGISTER_DIG_H2 | 0xE1 (0xE1-0xE7 (7)) |
BME280_REGISTER_PRESS | 0xF7 (0xF7-0xF9 (8)) |