C/C++ - Load Cell Bricklet

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

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#include <stdio.h>

#include "ip_connection.h"
#include "bricklet_load_cell.h"

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

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

    // Create device object
    LoadCell lc;
    load_cell_create(&lc, 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 weight
    int32_t weight;
    if(load_cell_get_weight(&lc, &weight) < 0) {
        fprintf(stderr, "Could not get weight, probably timeout\n");
        return 1;
    }

    printf("Weight: %d g\n", weight);

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

Callback

Download (example_callback.c)

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#include <stdio.h>

#include "ip_connection.h"
#include "bricklet_load_cell.h"

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

// Callback function for weight callback
void cb_weight(int32_t weight, void *user_data) {
    (void)user_data; // avoid unused parameter warning

    printf("Weight: %d g\n", weight);
}

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

    // Create device object
    LoadCell lc;
    load_cell_create(&lc, 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 weight callback to function cb_weight
    load_cell_register_callback(&lc,
                                LOAD_CELL_CALLBACK_WEIGHT,
                                (void (*)(void))cb_weight,
                                NULL);

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

    printf("Press key to exit\n");
    getchar();
    load_cell_destroy(&lc);
    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_load_cell.h"

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

// Callback function for weight reached callback
void cb_weight_reached(int32_t weight, void *user_data) {
    (void)user_data; // avoid unused parameter warning

    printf("Weight: %d g\n", weight);
}

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

    // Create device object
    LoadCell lc;
    load_cell_create(&lc, 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 1 second (1000ms)
    load_cell_set_debounce_period(&lc, 1000);

    // Register weight reached callback to function cb_weight_reached
    load_cell_register_callback(&lc,
                                LOAD_CELL_CALLBACK_WEIGHT_REACHED,
                                (void (*)(void))cb_weight_reached,
                                NULL);

    // Configure threshold for weight "greater than 200 g"
    load_cell_set_weight_callback_threshold(&lc, '>', 200, 0);

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

API

Most functions of the C/C++ bindings return an error code (e_code). Data returned from the device, when a getter is called, is handled via output parameters. 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 C/C++ 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
  • E_INVALID_UID = -13
  • E_NON_ASCII_CHAR_IN_SECRET = -14
  • E_WRONG_DEVICE_TYPE = -15
  • E_DEVICE_REPLACED = -16
  • E_WRONG_RESPONSE_LENGTH = -17

as defined in ip_connection.h.

All functions listed below are thread-safe.

Basic Functions

void load_cell_create(LoadCell *load_cell, const char *uid, IPConnection *ipcon)
Parameters:
  • load_cell – Type: LoadCell *
  • uid – Type: const char *
  • ipcon – Type: IPConnection *

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

LoadCell load_cell;
load_cell_create(&load_cell, "YOUR_DEVICE_UID", &ipcon);

This device object can be used after the IP connection has been connected.

void load_cell_destroy(LoadCell *load_cell)
Parameters:
  • load_cell – Type: LoadCell *

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

int load_cell_get_weight(LoadCell *load_cell, int32_t *ret_weight)
Parameters:
  • load_cell – Type: LoadCell *
Output Parameters:
  • ret_weight – Type: int32_t, Unit: 1 g, Range: [-231 to 231 - 1]
Returns:
  • e_code – Type: int

Returns the currently measured weight.

If you want to get the weight periodically, it is recommended to use the LOAD_CELL_CALLBACK_WEIGHT callback and set the period with load_cell_set_weight_callback_period().

int load_cell_led_on(LoadCell *load_cell)
Parameters:
  • load_cell – Type: LoadCell *
Returns:
  • e_code – Type: int

Turns the LED on.

int load_cell_led_off(LoadCell *load_cell)
Parameters:
  • load_cell – Type: LoadCell *
Returns:
  • e_code – Type: int

Turns the LED off.

int load_cell_is_led_on(LoadCell *load_cell, bool *ret_on)
Parameters:
  • load_cell – Type: LoadCell *
Output Parameters:
  • ret_on – Type: bool, Default: false
Returns:
  • e_code – Type: int

Returns true if the led is on, false otherwise.

int load_cell_tare(LoadCell *load_cell)
Parameters:
  • load_cell – Type: LoadCell *
Returns:
  • e_code – Type: int

Sets the currently measured weight as tare weight.

Advanced Functions

int load_cell_set_moving_average(LoadCell *load_cell, uint8_t average)
Parameters:
  • load_cell – Type: LoadCell *
  • average – Type: uint8_t, Range: [1 to 40], Default: 4
Returns:
  • e_code – Type: int

Sets the length of a moving averaging for the weight value.

Setting the length to 1 will turn the averaging off. With less averaging, there is more noise on the data.

int load_cell_get_moving_average(LoadCell *load_cell, uint8_t *ret_average)
Parameters:
  • load_cell – Type: LoadCell *
Output Parameters:
  • ret_average – Type: uint8_t, Range: [1 to 40], Default: 4
Returns:
  • e_code – Type: int

Returns the length moving average as set by load_cell_set_moving_average().

int load_cell_calibrate(LoadCell *load_cell, uint32_t weight)
Parameters:
  • load_cell – Type: LoadCell *
  • weight – Type: uint32_t, Unit: 1 g, Range: [0 to 232 - 1]
Returns:
  • e_code – Type: int

To calibrate your Load Cell Bricklet you have to

  • empty the scale and call this function with 0 and
  • add a known weight to the scale and call this function with the weight.

The calibration is saved in the EEPROM of the Bricklet and only needs to be done once.

We recommend to use the Brick Viewer for calibration, you don't need to call this function in your source code.

int load_cell_set_configuration(LoadCell *load_cell, uint8_t rate, uint8_t gain)
Parameters:
  • load_cell – Type: LoadCell *
  • rate – Type: uint8_t, Range: See constants, Default: 0
  • gain – Type: uint8_t, Range: See constants, Default: 0
Returns:
  • e_code – Type: int

The measurement rate and gain are configurable.

The rate can be either 10Hz or 80Hz. A faster rate will produce more noise. It is additionally possible to add a moving average (see load_cell_set_moving_average()) to the measurements.

The gain can be 128x, 64x or 32x. It represents a measurement range of ±20mV, ±40mV and ±80mV respectively. The Load Cell Bricklet uses an excitation voltage of 5V and most load cells use an output of 2mV/V. That means the voltage range is ±15mV for most load cells (i.e. gain of 128x is best). If you don't know what all of this means you should keep it at 128x, it will most likely be correct.

The configuration is saved in the EEPROM of the Bricklet and only needs to be done once.

We recommend to use the Brick Viewer for configuration, you don't need to call this function in your source code.

The following constants are available for this function:

For rate:

  • LOAD_CELL_RATE_10HZ = 0
  • LOAD_CELL_RATE_80HZ = 1

For gain:

  • LOAD_CELL_GAIN_128X = 0
  • LOAD_CELL_GAIN_64X = 1
  • LOAD_CELL_GAIN_32X = 2
int load_cell_get_configuration(LoadCell *load_cell, uint8_t *ret_rate, uint8_t *ret_gain)
Parameters:
  • load_cell – Type: LoadCell *
Output Parameters:
  • ret_rate – Type: uint8_t, Range: See constants, Default: 0
  • ret_gain – Type: uint8_t, Range: See constants, Default: 0
Returns:
  • e_code – Type: int

Returns the configuration as set by load_cell_set_configuration().

The following constants are available for this function:

For ret_rate:

  • LOAD_CELL_RATE_10HZ = 0
  • LOAD_CELL_RATE_80HZ = 1

For ret_gain:

  • LOAD_CELL_GAIN_128X = 0
  • LOAD_CELL_GAIN_64X = 1
  • LOAD_CELL_GAIN_32X = 2
int load_cell_get_identity(LoadCell *load_cell, 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)
Parameters:
  • load_cell – Type: LoadCell *
Output Parameters:
  • ret_uid – Type: char[8]
  • ret_connected_uid – Type: char[8]
  • ret_position – Type: char, Range: ['a' to 'h', 'z']
  • ret_hardware_version – Type: uint8_t[3]
    • 0: major – Type: uint8_t, Range: [0 to 255]
    • 1: minor – Type: uint8_t, Range: [0 to 255]
    • 2: revision – Type: uint8_t, Range: [0 to 255]
  • ret_firmware_version – Type: uint8_t[3]
    • 0: major – Type: uint8_t, Range: [0 to 255]
    • 1: minor – Type: uint8_t, Range: [0 to 255]
    • 2: revision – Type: uint8_t, Range: [0 to 255]
  • ret_device_identifier – Type: uint16_t, Range: [0 to 216 - 1]
Returns:
  • e_code – Type: int

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', 'd', 'e', 'f', 'g' or 'h' (Bricklet Port). A Bricklet connected to an Isolator Bricklet is always as position 'z'.

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

Callback Configuration Functions

void load_cell_register_callback(LoadCell *load_cell, int16_t callback_id, void (*function)(void), void *user_data)
Parameters:
  • load_cell – Type: LoadCell *
  • callback_id – Type: int16_t
  • function – Type: void (*)(void)
  • user_data – Type: void *

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 load_cell_set_weight_callback_period(LoadCell *load_cell, uint32_t period)
Parameters:
  • load_cell – Type: LoadCell *
  • period – Type: uint32_t, Unit: 1 ms, Range: [0 to 232 - 1], Default: 0
Returns:
  • e_code – Type: int

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

The LOAD_CELL_CALLBACK_WEIGHT callback is only triggered if the weight has changed since the last triggering.

int load_cell_get_weight_callback_period(LoadCell *load_cell, uint32_t *ret_period)
Parameters:
  • load_cell – Type: LoadCell *
Output Parameters:
  • ret_period – Type: uint32_t, Unit: 1 ms, Range: [0 to 232 - 1], Default: 0
Returns:
  • e_code – Type: int

Returns the period as set by load_cell_set_weight_callback_period().

int load_cell_set_weight_callback_threshold(LoadCell *load_cell, char option, int32_t min, int32_t max)
Parameters:
  • load_cell – Type: LoadCell *
  • option – Type: char, Range: See constants, Default: 'x'
  • min – Type: int32_t, Unit: 1 g, Range: [-231 to 231 - 1], Default: 0
  • max – Type: int32_t, Unit: 1 g, Range: [-231 to 231 - 1], Default: 0
Returns:
  • e_code – Type: int

Sets the thresholds for the LOAD_CELL_CALLBACK_WEIGHT_REACHED callback.

The following options are possible:

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

The following constants are available for this function:

For option:

  • LOAD_CELL_THRESHOLD_OPTION_OFF = 'x'
  • LOAD_CELL_THRESHOLD_OPTION_OUTSIDE = 'o'
  • LOAD_CELL_THRESHOLD_OPTION_INSIDE = 'i'
  • LOAD_CELL_THRESHOLD_OPTION_SMALLER = '<'
  • LOAD_CELL_THRESHOLD_OPTION_GREATER = '>'
int load_cell_get_weight_callback_threshold(LoadCell *load_cell, char *ret_option, int32_t *ret_min, int32_t *ret_max)
Parameters:
  • load_cell – Type: LoadCell *
Output Parameters:
  • ret_option – Type: char, Range: See constants, Default: 'x'
  • ret_min – Type: int32_t, Unit: 1 g, Range: [-231 to 231 - 1], Default: 0
  • ret_max – Type: int32_t, Unit: 1 g, Range: [-231 to 231 - 1], Default: 0
Returns:
  • e_code – Type: int

Returns the threshold as set by load_cell_set_weight_callback_threshold().

The following constants are available for this function:

For ret_option:

  • LOAD_CELL_THRESHOLD_OPTION_OFF = 'x'
  • LOAD_CELL_THRESHOLD_OPTION_OUTSIDE = 'o'
  • LOAD_CELL_THRESHOLD_OPTION_INSIDE = 'i'
  • LOAD_CELL_THRESHOLD_OPTION_SMALLER = '<'
  • LOAD_CELL_THRESHOLD_OPTION_GREATER = '>'
int load_cell_set_debounce_period(LoadCell *load_cell, uint32_t debounce)
Parameters:
  • load_cell – Type: LoadCell *
  • debounce – Type: uint32_t, Unit: 1 ms, Range: [0 to 232 - 1], Default: 100
Returns:
  • e_code – Type: int

Sets the period with which the threshold callback

is triggered, if the threshold

keeps being reached.

int load_cell_get_debounce_period(LoadCell *load_cell, uint32_t *ret_debounce)
Parameters:
  • load_cell – Type: LoadCell *
Output Parameters:
  • ret_debounce – Type: uint32_t, Unit: 1 ms, Range: [0 to 232 - 1], Default: 100
Returns:
  • e_code – Type: int

Returns the debounce period as set by load_cell_set_debounce_period().

Callbacks

Callbacks can be registered to receive time critical or recurring data from the device. The registration is done with the load_cell_register_callback() function:

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

load_cell_register_callback(&load_cell,
                            LOAD_CELL_CALLBACK_EXAMPLE,
                            (void (*)(void))my_callback,
                            NULL);

The available constants with corresponding 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.

LOAD_CELL_CALLBACK_WEIGHT
void callback(int32_t weight, void *user_data)
Callback Parameters:
  • weight – Type: int32_t, Unit: 1 g, Range: [-231 to 231 - 1]
  • user_data – Type: void *

This callback is triggered periodically with the period that is set by load_cell_set_weight_callback_period(). The parameter is the weight as measured by the load cell.

The LOAD_CELL_CALLBACK_WEIGHT callback is only triggered if the weight has changed since the last triggering.

LOAD_CELL_CALLBACK_WEIGHT_REACHED
void callback(int32_t weight, void *user_data)
Callback Parameters:
  • weight – Type: int32_t, Unit: 1 g, Range: [-231 to 231 - 1]
  • user_data – Type: void *

This callback is triggered when the threshold as set by load_cell_set_weight_callback_threshold() is reached. The parameter is the weight as measured by the load cell.

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

Virtual Functions

Virtual functions don't communicate with the device itself, but operate only on the API bindings device object. They can be called without the corresponding IP Connection object being connected.

int load_cell_get_api_version(LoadCell *load_cell, uint8_t ret_api_version[3])
Parameters:
  • load_cell – Type: LoadCell *
Output Parameters:
  • ret_api_version – Type: uint8_t[3]
    • 0: major – Type: uint8_t, Range: [0 to 255]
    • 1: minor – Type: uint8_t, Range: [0 to 255]
    • 2: revision – Type: uint8_t, Range: [0 to 255]
Returns:
  • e_code – Type: int

Returns the version of the API definition 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 load_cell_get_response_expected(LoadCell *load_cell, uint8_t function_id, bool *ret_response_expected)
Parameters:
  • load_cell – Type: LoadCell *
  • function_id – Type: uint8_t, Range: See constants
Output Parameters:
  • ret_response_expected – Type: bool
Returns:
  • e_code – Type: int

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 load_cell_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 sent and errors are silently ignored, because they cannot be detected.

The following constants are available for this function:

For function_id:

  • LOAD_CELL_FUNCTION_SET_WEIGHT_CALLBACK_PERIOD = 2
  • LOAD_CELL_FUNCTION_SET_WEIGHT_CALLBACK_THRESHOLD = 4
  • LOAD_CELL_FUNCTION_SET_DEBOUNCE_PERIOD = 6
  • LOAD_CELL_FUNCTION_SET_MOVING_AVERAGE = 8
  • LOAD_CELL_FUNCTION_LED_ON = 10
  • LOAD_CELL_FUNCTION_LED_OFF = 11
  • LOAD_CELL_FUNCTION_CALIBRATE = 13
  • LOAD_CELL_FUNCTION_TARE = 14
  • LOAD_CELL_FUNCTION_SET_CONFIGURATION = 15
int load_cell_set_response_expected(LoadCell *load_cell, uint8_t function_id, bool response_expected)
Parameters:
  • load_cell – Type: LoadCell *
  • function_id – Type: uint8_t, Range: See constants
  • response_expected – Type: bool
Returns:
  • e_code – Type: int

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 sent and errors are silently ignored, because they cannot be detected.

The following constants are available for this function:

For function_id:

  • LOAD_CELL_FUNCTION_SET_WEIGHT_CALLBACK_PERIOD = 2
  • LOAD_CELL_FUNCTION_SET_WEIGHT_CALLBACK_THRESHOLD = 4
  • LOAD_CELL_FUNCTION_SET_DEBOUNCE_PERIOD = 6
  • LOAD_CELL_FUNCTION_SET_MOVING_AVERAGE = 8
  • LOAD_CELL_FUNCTION_LED_ON = 10
  • LOAD_CELL_FUNCTION_LED_OFF = 11
  • LOAD_CELL_FUNCTION_CALIBRATE = 13
  • LOAD_CELL_FUNCTION_TARE = 14
  • LOAD_CELL_FUNCTION_SET_CONFIGURATION = 15
int load_cell_set_response_expected_all(LoadCell *load_cell, bool response_expected)
Parameters:
  • load_cell – Type: LoadCell *
  • response_expected – Type: bool
Returns:
  • e_code – Type: int

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

Constants

LOAD_CELL_DEVICE_IDENTIFIER

This constant is used to identify a Load Cell Bricklet.

The load_cell_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.

LOAD_CELL_DEVICE_DISPLAY_NAME

This constant represents the human readable name of a Load Cell Bricklet.