C/C++ - Barometer Bricklet

This is the description of the C/C++ API bindings for the Barometer Bricklet. General information and technical specifications for the Barometer Bricklet are summarized in its hardware description.

An installation guide for the C/C++ API bindings is part of their general description.

Examples

The example code below is Public Domain (CC0 1.0).

Callback

Download (example_callback.c)

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#include <stdio.h>

#include "ip_connection.h"
#include "bricklet_barometer.h"

#define HOST "localhost"
#define PORT 4223
#define UID "XYZ" // Change XYZ to the UID of your Barometer Bricklet

// Callback function for air pressure callback
void cb_air_pressure(int32_t air_pressure, void *user_data) {
    (void)user_data; // avoid unused parameter warning

    printf("Air Pressure: %f mbar\n", air_pressure/1000.0);
}

int main(void) {
    // Create IP connection
    IPConnection ipcon;
    ipcon_create(&ipcon);

    // Create device object
    Barometer b;
    barometer_create(&b, UID, &ipcon);

    // Connect to brickd
    if(ipcon_connect(&ipcon, HOST, PORT) < 0) {
        fprintf(stderr, "Could not connect\n");
        return 1;
    }
    // Don't use device before ipcon is connected

    // Register air pressure callback to function cb_air_pressure
    barometer_register_callback(&b,
                                BAROMETER_CALLBACK_AIR_PRESSURE,
                                (void *)cb_air_pressure,
                                NULL);

    // Set period for air pressure callback to 1s (1000ms)
    // Note: The air pressure callback is only called every second
    //       if the air pressure has changed since the last call!
    barometer_set_air_pressure_callback_period(&b, 1000);

    printf("Press key to exit\n");
    getchar();
    barometer_destroy(&b);
    ipcon_destroy(&ipcon); // Calls ipcon_disconnect internally
    return 0;
}

Simple

Download (example_simple.c)

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#include <stdio.h>

#include "ip_connection.h"
#include "bricklet_barometer.h"

#define HOST "localhost"
#define PORT 4223
#define UID "XYZ" // Change XYZ to the UID of your Barometer Bricklet

int main(void) {
    // Create IP connection
    IPConnection ipcon;
    ipcon_create(&ipcon);

    // Create device object
    Barometer b;
    barometer_create(&b, UID, &ipcon);

    // Connect to brickd
    if(ipcon_connect(&ipcon, HOST, PORT) < 0) {
        fprintf(stderr, "Could not connect\n");
        return 1;
    }
    // Don't use device before ipcon is connected

    // Get current air pressure
    int32_t air_pressure;
    if(barometer_get_air_pressure(&b, &air_pressure) < 0) {
        fprintf(stderr, "Could not get air pressure, probably timeout\n");
        return 1;
    }

    printf("Air Pressure: %f mbar\n", air_pressure/1000.0);

    // Get current altitude
    int32_t altitude;
    if(barometer_get_altitude(&b, &altitude) < 0) {
        fprintf(stderr, "Could not get altitude, probably timeout\n");
        return 1;
    }

    printf("Altitude: %f m\n", altitude/100.0);

    printf("Press key to exit\n");
    getchar();
    barometer_destroy(&b);
    ipcon_destroy(&ipcon); // Calls ipcon_disconnect internally
    return 0;
}

Threshold

Download (example_threshold.c)

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#include <stdio.h>

#include "ip_connection.h"
#include "bricklet_barometer.h"

#define HOST "localhost"
#define PORT 4223
#define UID "XYZ" // Change XYZ to the UID of your Barometer Bricklet

// Callback function for air pressure reached callback
void cb_air_pressure_reached(int32_t air_pressure, void *user_data) {
    (void)user_data; // avoid unused parameter warning

    printf("Air Pressure: %f mbar\n", air_pressure/1000.0);
    printf("Enjoy the potentially good weather!\n");
}

int main(void) {
    // Create IP connection
    IPConnection ipcon;
    ipcon_create(&ipcon);

    // Create device object
    Barometer b;
    barometer_create(&b, UID, &ipcon);

    // Connect to brickd
    if(ipcon_connect(&ipcon, HOST, PORT) < 0) {
        fprintf(stderr, "Could not connect\n");
        return 1;
    }
    // Don't use device before ipcon is connected

    // Get threshold callbacks with a debounce time of 10 seconds (10000ms)
    barometer_set_debounce_period(&b, 10000);

    // Register air pressure reached callback to function cb_air_pressure_reached
    barometer_register_callback(&b,
                                BAROMETER_CALLBACK_AIR_PRESSURE_REACHED,
                                (void *)cb_air_pressure_reached,
                                NULL);

    // Configure threshold for air pressure "greater than 1025 mbar"
    barometer_set_air_pressure_callback_threshold(&b, '>', 1025*1000, 0);

    printf("Press key to exit\n");
    getchar();
    barometer_destroy(&b);
    ipcon_destroy(&ipcon); // Calls ipcon_disconnect internally
    return 0;
}

API

Every function of the C/C++ bindings returns an integer which describes an error code. Data returned from the device, when a getter is called, is handled via call by reference. These parameters are labeled with the ret_ prefix.

Possible error codes are:

  • E_OK = 0
  • E_TIMEOUT = -1
  • E_NO_STREAM_SOCKET = -2
  • E_HOSTNAME_INVALID = -3
  • E_NO_CONNECT = -4
  • E_NO_THREAD = -5
  • E_NOT_ADDED = -6 (unused since bindings version 2.0.0)
  • E_ALREADY_CONNECTED = -7
  • E_NOT_CONNECTED = -8
  • E_INVALID_PARAMETER = -9
  • E_NOT_SUPPORTED = -10
  • E_UNKNOWN_ERROR_CODE = -11
  • E_STREAM_OUT_OF_SYNC = -12

as defined in ip_connection.h.

All functions listed below are thread-safe.

Basic Functions

void barometer_create(Barometer *barometer, const char *uid, IPConnection *ipcon)

Creates the device object barometer with the unique device ID uid and adds it to the IPConnection ipcon:

Barometer barometer;
barometer_create(&barometer, "YOUR_DEVICE_UID", &ipcon);

This device object can be used after the IP connection has been connected (see examples above).

void barometer_destroy(Barometer *barometer)

Removes the device object barometer from its IPConnection and destroys it. The device object cannot be used anymore afterwards.

int barometer_get_air_pressure(Barometer *barometer, int32_t *ret_air_pressure)

Returns the air pressure of the air pressure sensor. The value has a range of 10000 to 1200000 and is given in mbar/1000, i.e. a value of 1001092 means that an air pressure of 1001.092 mbar is measured.

If you want to get the air pressure periodically, it is recommended to use the BAROMETER_CALLBACK_AIR_PRESSURE callback and set the period with barometer_set_air_pressure_callback_period().

int barometer_get_altitude(Barometer *barometer, int32_t *ret_altitude)

Returns the relative altitude of the air pressure sensor. The value is given in cm and is calculated based on the difference between the current air pressure and the reference air pressure that can be set with barometer_set_reference_air_pressure().

If you want to get the altitude periodically, it is recommended to use the BAROMETER_CALLBACK_ALTITUDE callback and set the period with barometer_set_altitude_callback_period().

int barometer_set_reference_air_pressure(Barometer *barometer, int32_t air_pressure)

Sets the reference air pressure in mbar/1000 for the altitude calculation. Valid values are between 10000 and 1200000. Setting the reference to the current air pressure results in a calculated altitude of 0cm. Passing 0 is a shortcut for passing the current air pressure as reference.

Well known reference values are the Q codes QNH and QFE used in aviation.

The default value is 1013.25mbar.

int barometer_get_reference_air_pressure(Barometer *barometer, int32_t *ret_air_pressure)

Returns the reference air pressure as set by barometer_set_reference_air_pressure().

Advanced Functions

int barometer_get_chip_temperature(Barometer *barometer, int16_t *ret_temperature)

Returns the temperature of the air pressure sensor. The value has a range of -4000 to 8500 and is given in °C/100, i.e. a value of 2007 means that a temperature of 20.07 °C is measured.

This temperature is used internally for temperature compensation of the air pressure measurement. It is not as accurate as the temperature measured by the Temperature Bricklet or the Temperature IR Bricklet.

int barometer_set_averaging(Barometer *barometer, uint8_t moving_average_pressure, uint8_t average_pressure, uint8_t average_temperature)

Sets the different averaging parameters. It is possible to set the length of a normal averaging for the temperature and pressure, as well as an additional length of a moving average for the pressure. The moving average is calculated from the normal averages. There is no moving average for the temperature.

The maximum length for the pressure average is 10, for the temperature average is 255 and for the moving average is 25.

Setting the all three parameters to 0 will turn the averaging completely off. If the averaging is off, there is lots of noise on the data, but the data is without delay. Thus we recommend to turn the averaging off if the Barometer Bricklet data is to be used for sensor fusion with other sensors.

The default values are 10 for the normal averages and 25 for the moving average.

New in version 2.0.1 (Plugin).

int barometer_get_averaging(Barometer *barometer, uint8_t *ret_moving_average_pressure, uint8_t *ret_average_pressure, uint8_t *ret_average_temperature)

Returns the averaging configuration as set by barometer_set_averaging().

New in version 2.0.1 (Plugin).

int barometer_get_api_version(Barometer *barometer, uint8_t ret_api_version[3])

Returns the version of the API definition (major, minor, revision) implemented by this API bindings. This is neither the release version of this API bindings nor does it tell you anything about the represented Brick or Bricklet.

int barometer_get_response_expected(Barometer *barometer, uint8_t function_id, bool *ret_response_expected)

Returns the response expected flag for the function specified by the function ID parameter. It is true if the function is expected to send a response, false otherwise.

For getter functions this is enabled by default and cannot be disabled, because those functions will always send a response. For callback configuration functions it is enabled by default too, but can be disabled by barometer_set_response_expected(). For setter functions it is disabled by default and can be enabled.

Enabling the response expected flag for a setter function allows to detect timeouts and other error conditions calls of this setter as well. The device will then send a response for this purpose. If this flag is disabled for a setter function then no response is send and errors are silently ignored, because they cannot be detected.

See barometer_set_response_expected() for the list of function ID defines available for this function.

int barometer_set_response_expected(Barometer *barometer, uint8_t function_id, bool response_expected)

Changes the response expected flag of the function specified by the function ID parameter. This flag can only be changed for setter (default value: false) and callback configuration functions (default value: true). For getter functions it is always enabled.

Enabling the response expected flag for a setter function allows to detect timeouts and other error conditions calls of this setter as well. The device will then send a response for this purpose. If this flag is disabled for a setter function then no response is send and errors are silently ignored, because they cannot be detected.

The following function ID defines are available for this function:

  • BAROMETER_FUNCTION_SET_AIR_PRESSURE_CALLBACK_PERIOD = 3
  • BAROMETER_FUNCTION_SET_ALTITUDE_CALLBACK_PERIOD = 5
  • BAROMETER_FUNCTION_SET_AIR_PRESSURE_CALLBACK_THRESHOLD = 7
  • BAROMETER_FUNCTION_SET_ALTITUDE_CALLBACK_THRESHOLD = 9
  • BAROMETER_FUNCTION_SET_DEBOUNCE_PERIOD = 11
  • BAROMETER_FUNCTION_SET_REFERENCE_AIR_PRESSURE = 13
  • BAROMETER_FUNCTION_SET_AVERAGING = 20
int barometer_set_response_expected_all(Barometer *barometer, bool response_expected)

Changes the response expected flag for all setter and callback configuration functions of this device at once.

int barometer_get_identity(Barometer *barometer, char ret_uid[8], char ret_connected_uid[8], char *ret_position, uint8_t ret_hardware_version[3], uint8_t ret_firmware_version[3], uint16_t *ret_device_identifier)

Returns the UID, the UID where the Bricklet is connected to, the position, the hardware and firmware version as well as the device identifier.

The position can be 'a', 'b', 'c' or 'd'.

The device identifier numbers can be found here. There is also a constant for the device identifier of this Bricklet.

Callback Configuration Functions

void barometer_register_callback(Barometer *barometer, int16_t callback_id, void *function, void *user_data)

Registers the given function with the given callback_id. The user_data will be passed as the last parameter to the function.

The available callback IDs with corresponding function signatures are listed below.

int barometer_set_air_pressure_callback_period(Barometer *barometer, uint32_t period)

Sets the period in ms with which the BAROMETER_CALLBACK_AIR_PRESSURE callback is triggered periodically. A value of 0 turns the callback off.

The BAROMETER_CALLBACK_AIR_PRESSURE callback is only triggered if the air pressure has changed since the last triggering.

The default value is 0.

int barometer_get_air_pressure_callback_period(Barometer *barometer, uint32_t *ret_period)

Returns the period as set by barometer_set_air_pressure_callback_period().

int barometer_set_altitude_callback_period(Barometer *barometer, uint32_t period)

Sets the period in ms with which the BAROMETER_CALLBACK_ALTITUDE callback is triggered periodically. A value of 0 turns the callback off.

The BAROMETER_CALLBACK_ALTITUDE callback is only triggered if the altitude has changed since the last triggering.

The default value is 0.

int barometer_get_altitude_callback_period(Barometer *barometer, uint32_t *ret_period)

Returns the period as set by barometer_set_altitude_callback_period().

int barometer_set_air_pressure_callback_threshold(Barometer *barometer, char option, int32_t min, int32_t max)

Sets the thresholds for the BAROMETER_CALLBACK_AIR_PRESSURE_REACHED callback.

The following options are possible:

Option Description
'x' Callback is turned off
'o' Callback is triggered when the air pressure is outside the min and max values
'i' Callback is triggered when the air pressure is inside the min and max values
'<' Callback is triggered when the air pressure is smaller than the min value (max is ignored)
'>' Callback is triggered when the air pressure is greater than the min value (max is ignored)

The default value is ('x', 0, 0).

The following defines are available for this function:

  • BAROMETER_THRESHOLD_OPTION_OFF = 'x'
  • BAROMETER_THRESHOLD_OPTION_OUTSIDE = 'o'
  • BAROMETER_THRESHOLD_OPTION_INSIDE = 'i'
  • BAROMETER_THRESHOLD_OPTION_SMALLER = '<'
  • BAROMETER_THRESHOLD_OPTION_GREATER = '>'
int barometer_get_air_pressure_callback_threshold(Barometer *barometer, char *ret_option, int32_t *ret_min, int32_t *ret_max)

Returns the threshold as set by barometer_set_air_pressure_callback_threshold().

The following defines are available for this function:

  • BAROMETER_THRESHOLD_OPTION_OFF = 'x'
  • BAROMETER_THRESHOLD_OPTION_OUTSIDE = 'o'
  • BAROMETER_THRESHOLD_OPTION_INSIDE = 'i'
  • BAROMETER_THRESHOLD_OPTION_SMALLER = '<'
  • BAROMETER_THRESHOLD_OPTION_GREATER = '>'
int barometer_set_altitude_callback_threshold(Barometer *barometer, char option, int32_t min, int32_t max)

Sets the thresholds for the BAROMETER_CALLBACK_ALTITUDE_REACHED callback.

The following options are possible:

Option Description
'x' Callback is turned off
'o' Callback is triggered when the altitude is outside the min and max values
'i' Callback is triggered when the altitude is inside the min and max values
'<' Callback is triggered when the altitude is smaller than the min value (max is ignored)
'>' Callback is triggered when the altitude is greater than the min value (max is ignored)

The default value is ('x', 0, 0).

The following defines are available for this function:

  • BAROMETER_THRESHOLD_OPTION_OFF = 'x'
  • BAROMETER_THRESHOLD_OPTION_OUTSIDE = 'o'
  • BAROMETER_THRESHOLD_OPTION_INSIDE = 'i'
  • BAROMETER_THRESHOLD_OPTION_SMALLER = '<'
  • BAROMETER_THRESHOLD_OPTION_GREATER = '>'
int barometer_get_altitude_callback_threshold(Barometer *barometer, char *ret_option, int32_t *ret_min, int32_t *ret_max)

Returns the threshold as set by barometer_set_altitude_callback_threshold().

The following defines are available for this function:

  • BAROMETER_THRESHOLD_OPTION_OFF = 'x'
  • BAROMETER_THRESHOLD_OPTION_OUTSIDE = 'o'
  • BAROMETER_THRESHOLD_OPTION_INSIDE = 'i'
  • BAROMETER_THRESHOLD_OPTION_SMALLER = '<'
  • BAROMETER_THRESHOLD_OPTION_GREATER = '>'
int barometer_set_debounce_period(Barometer *barometer, uint32_t debounce)

Sets the period in ms with which the threshold callbacks

are triggered, if the thresholds

keep being reached.

The default value is 100.

int barometer_get_debounce_period(Barometer *barometer, uint32_t *ret_debounce)

Returns the debounce period as set by barometer_set_debounce_period().

Callbacks

Callbacks can be registered to receive time critical or recurring data from the device. The registration is done with the barometer_register_callback() function. The parameters consist of the device object, the callback ID, the callback function and optional user data:

void my_callback(int p, void *user_data) {
    printf("parameter: %d\n", p);
}

barometer_register_callback(&barometer, BAROMETER_CALLBACK_EXAMPLE, (void *)my_callback, NULL);

The available constants with corresponding callback function signatures are described below.

Note

Using callbacks for recurring events is always preferred compared to using getters. It will use less USB bandwidth and the latency will be a lot better, since there is no round trip time.

BAROMETER_CALLBACK_AIR_PRESSURE
void callback(int32_t air_pressure, void *user_data)

This callback is triggered periodically with the period that is set by barometer_set_air_pressure_callback_period(). The parameter is the air pressure of the air pressure sensor.

The BAROMETER_CALLBACK_AIR_PRESSURE callback is only triggered if the air pressure has changed since the last triggering.

BAROMETER_CALLBACK_ALTITUDE
void callback(int32_t altitude, void *user_data)

This callback is triggered periodically with the period that is set by barometer_set_altitude_callback_period(). The parameter is the altitude of the air pressure sensor.

The BAROMETER_CALLBACK_ALTITUDE callback is only triggered if the altitude has changed since the last triggering.

BAROMETER_CALLBACK_AIR_PRESSURE_REACHED
void callback(int32_t air_pressure, void *user_data)

This callback is triggered when the threshold as set by barometer_set_air_pressure_callback_threshold() is reached. The parameter is the air pressure of the air pressure sensor.

If the threshold keeps being reached, the callback is triggered periodically with the period as set by barometer_set_debounce_period().

BAROMETER_CALLBACK_ALTITUDE_REACHED
void callback(int32_t altitude, void *user_data)

This callback is triggered when the threshold as set by barometer_set_altitude_callback_threshold() is reached. The parameter is the altitude of the air pressure sensor.

If the threshold keeps being reached, the callback is triggered periodically with the period as set by barometer_set_debounce_period().

Constants

BAROMETER_DEVICE_IDENTIFIER

This constant is used to identify a Barometer Bricklet.

The barometer_get_identity() function and the IPCON_CALLBACK_ENUMERATE callback of the IP Connection have a device_identifier parameter to specify the Brick's or Bricklet's type.

BAROMETER_DEVICE_DISPLAY_NAME

This constant represents the human readable name of a Barometer Bricklet.