C/C++ - Accelerometer Bricklet

This is the description of the C/C++ API bindings for the Accelerometer Bricklet. General information and technical specifications for the Accelerometer 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).

Simple

Download (example_simple.c)

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
#include <stdio.h>

#include "ip_connection.h"
#include "bricklet_accelerometer.h"

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

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

    // Create device object
    Accelerometer a;
    accelerometer_create(&a, 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 acceleration
    int16_t x, y, z;
    if(accelerometer_get_acceleration(&a, &x, &y, &z) < 0) {
        fprintf(stderr, "Could not get acceleration, probably timeout\n");
        return 1;
    }

    printf("Acceleration [X]: %f g\n", x/1000.0);
    printf("Acceleration [Y]: %f g\n", y/1000.0);
    printf("Acceleration [Z]: %f g\n", z/1000.0);

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

Callback

Download (example_callback.c)

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
#include <stdio.h>

#include "ip_connection.h"
#include "bricklet_accelerometer.h"

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

// Callback function for acceleration callback
void cb_acceleration(int16_t x, int16_t y, int16_t z, void *user_data) {
    (void)user_data; // avoid unused parameter warning

    printf("Acceleration [X]: %f g\n", x/1000.0);
    printf("Acceleration [Y]: %f g\n", y/1000.0);
    printf("Acceleration [Z]: %f g\n", z/1000.0);
    printf("\n");
}

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

    // Create device object
    Accelerometer a;
    accelerometer_create(&a, 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 acceleration callback to function cb_acceleration
    accelerometer_register_callback(&a,
                                    ACCELEROMETER_CALLBACK_ACCELERATION,
                                    (void *)cb_acceleration,
                                    NULL);

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

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

Threshold

Download (example_threshold.c)

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
#include <stdio.h>

#include "ip_connection.h"
#include "bricklet_accelerometer.h"

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

// Callback function for acceleration reached callback
void cb_acceleration_reached(int16_t x, int16_t y, int16_t z, void *user_data) {
    (void)user_data; // avoid unused parameter warning

    printf("Acceleration [X]: %f g\n", x/1000.0);
    printf("Acceleration [Y]: %f g\n", y/1000.0);
    printf("Acceleration [Z]: %f g\n", z/1000.0);
    printf("\n");
}

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

    // Create device object
    Accelerometer a;
    accelerometer_create(&a, 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)
    accelerometer_set_debounce_period(&a, 10000);

    // Register acceleration reached callback to function cb_acceleration_reached
    accelerometer_register_callback(&a,
                                    ACCELEROMETER_CALLBACK_ACCELERATION_REACHED,
                                    (void *)cb_acceleration_reached,
                                    NULL);

    // Configure threshold for acceleration "greater than 2 g, 2 g, 2 g"
    accelerometer_set_acceleration_callback_threshold(&a, '>', 2*1000, 0, 2*1000, 0, 2*1000, 0);

    printf("Press key to exit\n");
    getchar();
    accelerometer_destroy(&a);
    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 accelerometer_create(Accelerometer *accelerometer, const char *uid, IPConnection *ipcon)

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

Accelerometer accelerometer;
accelerometer_create(&accelerometer, "YOUR_DEVICE_UID", &ipcon);

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

void accelerometer_destroy(Accelerometer *accelerometer)

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

int accelerometer_get_acceleration(Accelerometer *accelerometer, int16_t *ret_x, int16_t *ret_y, int16_t *ret_z)

Returns the acceleration in x, y and z direction. The values are given in g/1000 (1g = 9.80665m/s²), not to be confused with grams.

If you want to get the acceleration periodically, it is recommended to use the ACCELEROMETER_CALLBACK_ACCELERATION callback and set the period with accelerometer_set_acceleration_callback_period().

int accelerometer_get_temperature(Accelerometer *accelerometer, int16_t *ret_temperature)

Returns the temperature of the accelerometer in °C.

int accelerometer_led_on(Accelerometer *accelerometer)

Enables the LED on the Bricklet.

int accelerometer_led_off(Accelerometer *accelerometer)

Disables the LED on the Bricklet.

int accelerometer_is_led_on(Accelerometer *accelerometer, bool *ret_on)

Returns true if the LED is enabled, false otherwise.

Advanced Functions

int accelerometer_set_configuration(Accelerometer *accelerometer, uint8_t data_rate, uint8_t full_scale, uint8_t filter_bandwidth)

Configures the data rate, full scale range and filter bandwidth. Possible values are:

  • Data rate of 0Hz to 1600Hz.
  • Full scale range of -2G to +2G up to -16G to +16G.
  • Filter bandwidth between 50Hz and 800Hz.

Decreasing data rate or full scale range will also decrease the noise on the data.

The default values are 100Hz data rate, -4G to +4G range and 200Hz filter bandwidth.

The following defines are available for this function:

  • ACCELEROMETER_DATA_RATE_OFF = 0
  • ACCELEROMETER_DATA_RATE_3HZ = 1
  • ACCELEROMETER_DATA_RATE_6HZ = 2
  • ACCELEROMETER_DATA_RATE_12HZ = 3
  • ACCELEROMETER_DATA_RATE_25HZ = 4
  • ACCELEROMETER_DATA_RATE_50HZ = 5
  • ACCELEROMETER_DATA_RATE_100HZ = 6
  • ACCELEROMETER_DATA_RATE_400HZ = 7
  • ACCELEROMETER_DATA_RATE_800HZ = 8
  • ACCELEROMETER_DATA_RATE_1600HZ = 9
  • ACCELEROMETER_FULL_SCALE_2G = 0
  • ACCELEROMETER_FULL_SCALE_4G = 1
  • ACCELEROMETER_FULL_SCALE_6G = 2
  • ACCELEROMETER_FULL_SCALE_8G = 3
  • ACCELEROMETER_FULL_SCALE_16G = 4
  • ACCELEROMETER_FILTER_BANDWIDTH_800HZ = 0
  • ACCELEROMETER_FILTER_BANDWIDTH_400HZ = 1
  • ACCELEROMETER_FILTER_BANDWIDTH_200HZ = 2
  • ACCELEROMETER_FILTER_BANDWIDTH_50HZ = 3
int accelerometer_get_configuration(Accelerometer *accelerometer, uint8_t *ret_data_rate, uint8_t *ret_full_scale, uint8_t *ret_filter_bandwidth)

Returns the configuration as set by accelerometer_set_configuration().

The following defines are available for this function:

  • ACCELEROMETER_DATA_RATE_OFF = 0
  • ACCELEROMETER_DATA_RATE_3HZ = 1
  • ACCELEROMETER_DATA_RATE_6HZ = 2
  • ACCELEROMETER_DATA_RATE_12HZ = 3
  • ACCELEROMETER_DATA_RATE_25HZ = 4
  • ACCELEROMETER_DATA_RATE_50HZ = 5
  • ACCELEROMETER_DATA_RATE_100HZ = 6
  • ACCELEROMETER_DATA_RATE_400HZ = 7
  • ACCELEROMETER_DATA_RATE_800HZ = 8
  • ACCELEROMETER_DATA_RATE_1600HZ = 9
  • ACCELEROMETER_FULL_SCALE_2G = 0
  • ACCELEROMETER_FULL_SCALE_4G = 1
  • ACCELEROMETER_FULL_SCALE_6G = 2
  • ACCELEROMETER_FULL_SCALE_8G = 3
  • ACCELEROMETER_FULL_SCALE_16G = 4
  • ACCELEROMETER_FILTER_BANDWIDTH_800HZ = 0
  • ACCELEROMETER_FILTER_BANDWIDTH_400HZ = 1
  • ACCELEROMETER_FILTER_BANDWIDTH_200HZ = 2
  • ACCELEROMETER_FILTER_BANDWIDTH_50HZ = 3
int accelerometer_get_api_version(Accelerometer *accelerometer, 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 accelerometer_get_response_expected(Accelerometer *accelerometer, 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 accelerometer_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 accelerometer_set_response_expected() for the list of function ID defines available for this function.

int accelerometer_set_response_expected(Accelerometer *accelerometer, 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:

  • ACCELEROMETER_FUNCTION_SET_ACCELERATION_CALLBACK_PERIOD = 2
  • ACCELEROMETER_FUNCTION_SET_ACCELERATION_CALLBACK_THRESHOLD = 4
  • ACCELEROMETER_FUNCTION_SET_DEBOUNCE_PERIOD = 6
  • ACCELEROMETER_FUNCTION_SET_CONFIGURATION = 9
  • ACCELEROMETER_FUNCTION_LED_ON = 11
  • ACCELEROMETER_FUNCTION_LED_OFF = 12
int accelerometer_set_response_expected_all(Accelerometer *accelerometer, bool response_expected)

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

int accelerometer_get_identity(Accelerometer *accelerometer, 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 accelerometer_register_callback(Accelerometer *accelerometer, 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 accelerometer_set_acceleration_callback_period(Accelerometer *accelerometer, uint32_t period)

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

The ACCELEROMETER_CALLBACK_ACCELERATION callback is only triggered if the acceleration has changed since the last triggering.

The default value is 0.

int accelerometer_get_acceleration_callback_period(Accelerometer *accelerometer, uint32_t *ret_period)

Returns the period as set by accelerometer_set_acceleration_callback_period().

int accelerometer_set_acceleration_callback_threshold(Accelerometer *accelerometer, char option, int16_t min_x, int16_t max_x, int16_t min_y, int16_t max_y, int16_t min_z, int16_t max_z)

Sets the thresholds for the ACCELEROMETER_CALLBACK_ACCELERATION_REACHED callback.

The following options are possible:

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

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

The following defines are available for this function:

  • ACCELEROMETER_THRESHOLD_OPTION_OFF = 'x'
  • ACCELEROMETER_THRESHOLD_OPTION_OUTSIDE = 'o'
  • ACCELEROMETER_THRESHOLD_OPTION_INSIDE = 'i'
  • ACCELEROMETER_THRESHOLD_OPTION_SMALLER = '<'
  • ACCELEROMETER_THRESHOLD_OPTION_GREATER = '>'
int accelerometer_get_acceleration_callback_threshold(Accelerometer *accelerometer, char *ret_option, int16_t *ret_min_x, int16_t *ret_max_x, int16_t *ret_min_y, int16_t *ret_max_y, int16_t *ret_min_z, int16_t *ret_max_z)

Returns the threshold as set by accelerometer_set_acceleration_callback_threshold().

The following defines are available for this function:

  • ACCELEROMETER_THRESHOLD_OPTION_OFF = 'x'
  • ACCELEROMETER_THRESHOLD_OPTION_OUTSIDE = 'o'
  • ACCELEROMETER_THRESHOLD_OPTION_INSIDE = 'i'
  • ACCELEROMETER_THRESHOLD_OPTION_SMALLER = '<'
  • ACCELEROMETER_THRESHOLD_OPTION_GREATER = '>'
int accelerometer_set_debounce_period(Accelerometer *accelerometer, uint32_t debounce)

Sets the period in ms with which the threshold callback

is triggered, if the threshold

keeps being reached.

The default value is 100.

int accelerometer_get_debounce_period(Accelerometer *accelerometer, uint32_t *ret_debounce)

Returns the debounce period as set by accelerometer_set_debounce_period().

Callbacks

Callbacks can be registered to receive time critical or recurring data from the device. The registration is done with the accelerometer_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);
}

accelerometer_register_callback(&accelerometer, ACCELEROMETER_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.

ACCELEROMETER_CALLBACK_ACCELERATION
void callback(int16_t x, int16_t y, int16_t z, void *user_data)

This callback is triggered periodically with the period that is set by accelerometer_set_acceleration_callback_period(). The parameters are the X, Y and Z acceleration.

The ACCELEROMETER_CALLBACK_ACCELERATION callback is only triggered if the acceleration has changed since the last triggering.

ACCELEROMETER_CALLBACK_ACCELERATION_REACHED
void callback(int16_t x, int16_t y, int16_t z, void *user_data)

This callback is triggered when the threshold as set by accelerometer_set_acceleration_callback_threshold() is reached. The parameters are the X, Y and Z acceleration.

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

Constants

ACCELEROMETER_DEVICE_IDENTIFIER

This constant is used to identify a Accelerometer Bricklet.

The accelerometer_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.

ACCELEROMETER_DEVICE_DISPLAY_NAME

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