Barometer_BMP

Description

Interface to the BMP280 barometer.

<rc/bmp.h>

Author

James Strawson

Date

3/14/2018

Data Structures
struct	rc_bmp_data_t

Typedefs
typedef enum rc_bmp_oversample_t	rc_bmp_oversample_t
typedef enum rc_bmp_filter_t	rc_bmp_filter_t
typedef struct rc_bmp_data_t	rc_bmp_data_t

Functions
int	rc_bmp_init (rc_bmp_oversample_t oversample, rc_bmp_filter_t filter)
	powers on the barometer and initializes it with the given oversample and filter settings. More...
int	rc_bmp_set_sea_level_pressure_pa (double pa)
	If you know the current sea level pressure for your region and weather, you can use this to correct the altititude reading. More...
int	rc_bmp_power_off (void)
	Puts the barometer into a low power state, should be called at the end of your program before close. More...
int	rc_bmp_read (rc_bmp_data_t *data)
	Reads the newest temperature and pressure measurments from the barometer over the I2C bus. More...

Enumeration Type Documentation

rc_bmp_oversample_t

enum rc_bmp_oversample_t

Setting given to rc_bmp_init which defines the oversampling done internally to the barometer. For example, if BMP_OVERSAMPLE_16 is used then the barometer will average 16 samples before updating the data registers. The more oversampling used, the slower the data registers will update. You should pick an oversample that provides an update rate slightly slower than the rate at which you will be reading the barometer.

Enumerator
BMP_OVERSAMPLE_1	update rate 182 HZ
BMP_OVERSAMPLE_2	update rate 133 HZ
BMP_OVERSAMPLE_4	update rate 87 HZ
BMP_OVERSAMPLE_8	update rate 51 HZ
BMP_OVERSAMPLE_16	update rate 28 HZ

rc_bmp_filter_t

enum rc_bmp_filter_t

Setting given to rc_bmp_init to configure the coefficient of the internal first order filter. We recommend disabling the filter with BMP_FILTER_OFF and doing your own filtering with the discrete filter functions below.

Enumerator
BMP_FILTER_OFF
BMP_FILTER_2
BMP_FILTER_4
BMP_FILTER_8
BMP_FILTER_16

Function Documentation

rc_bmp_init()

int rc_bmp_init	(	rc_bmp_oversample_t	oversample,
		rc_bmp_filter_t	filter
	)

powers on the barometer and initializes it with the given oversample and filter settings.

Optionally call rc_bmp_set_sea_level_pressure_pa afterwards to change the sea level pressure from default.

Parameters

[in]	oversample	see rc_bmp_oversample_t
[in]	filter	see rc_bmp_filter_t

Returns

0 on success, otherwise -1.

Examples:

rc_altitude.c, and rc_test_bmp.c.

rc_bmp_set_sea_level_pressure_pa()

int rc_bmp_set_sea_level_pressure_pa

(

double

pa

)

If you know the current sea level pressure for your region and weather, you can use this to correct the altititude reading.

This is not necessary if you only care about differential altitude from a starting point. Must be called after rc_bmp_init to have an effect.

Parameters

[in]

pa

sea level pressure in pascals

Returns

0 on success, -1 on failure

rc_bmp_power_off()

int rc_bmp_power_off

(

void

)

Puts the barometer into a low power state, should be called at the end of your program before close.

Returns

0 on success, -1 on failure

Examples:

rc_altitude.c, and rc_test_bmp.c.

rc_bmp_read()

int rc_bmp_read

(

rc_bmp_data_t *

data

)

Reads the newest temperature and pressure measurments from the barometer over the I2C bus.

Parameters

data	pointer to data struct where new data will be written.

Returns

0 on success, -1 on failure

Examples:

rc_altitude.c, and rc_test_bmp.c.