Note
This Bricklet is currently in the prototype stage and the software/hardware as well as the documentation is in an incomplete state.
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.
The example code below is Public Domain (CC0 1.0).
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 | #include <stdio.h>
#include "ip_connection.h"
#include "bricklet_load_cell.h"
#define HOST "localhost"
#define PORT 4223
#define UID "XYZ" // Change to your UID
int main() {
// 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");
exit(1);
}
// Don't use device before ipcon is connected
// Get current weight (unit is g)
int32_t weight;
if(load_cell_get_weight(&lc, &weight) < 0) {
fprintf(stderr, "Could not get value, probably timeout\n");
exit(1);
}
printf("Weight: %f kg\n", weight/1000.0);
printf("Press key to exit\n");
getchar();
ipcon_destroy(&ipcon); // Calls ipcon_disconnect internally
}
|
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 | #include <stdio.h>
#include "ip_connection.h"
#include "bricklet_load_cell.h"
#define HOST "localhost"
#define PORT 4223
#define UID "XYZ" // Change to your UID
// Callback function for weight callback (parameter has unit g/10)
void cb_weight(uint16_t weight, void *user_data) {
(void)user_data; // avoid unused parameter warning
printf("Weight: %f kg\n", weight/1000.0);
}
int main() {
// 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");
exit(1);
}
// Don't use device before ipcon is connected
// 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);
// Register weight callback to function cb_weight
load_cell_register_callback(&lc,
LOAD_CELL_CALLBACK_WEIGHT,
(void *)cb_weight,
NULL);
printf("Press key to exit\n");
getchar();
ipcon_destroy(&ipcon); // Calls ipcon_disconnect internally
}
|
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 | #include <stdio.h>
#include "ip_connection.h"
#include "bricklet_load_cell.h"
#define HOST "localhost"
#define PORT 4223
#define UID "XYZ" // Change to your UID
// Callback for weight greater than 200 g
void cb_reached(uint16_t weight, void *user_data) {
(void)user_data; // avoid unused parameter warning
printf("Weight %f kg\n", weight/1000.0);
}
int main() {
// 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");
exit(1);
}
// Don't use device before ipcon is connected
// Get threshold callbacks with a debounce time of 10 seconds (10000ms)
load_cell_set_debounce_period(&lc, 10000);
// Register threshold reached callback to function cb_reached
load_cell_register_callback(&lc,
LOAD_CELL_CALLBACK_WEIGHT_REACHED,
(void *)cb_reached,
NULL);
// Configure threshold for "greater than 200 g"
load_cell_set_weight_callback_threshold(&lc, '>', 200, 0);
printf("Press key to exit\n");
getchar();
ipcon_destroy(&ipcon); // Calls ipcon_disconnect internally
}
|
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:
as defined in ip_connection.h.
All functions listed below are thread-safe.
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 (see examples above).
Removes the device object load_cell from its IPConnection and destroys it. The device object cannot be used anymore afterwards.
Returns the currently measured weight in grams.
If you want to get the weight periodically, it is recommended to use the callback LOAD_CELL_CALLBACK_WEIGHT and set the period with load_cell_set_weight_callback_period().
Turns the LED on.
Turns the LED off.
Returns true if the led is on, false otherwise.
Sets the currently measured weight as tare weight.
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.
The range for the averaging is 1-40.
The default value is 4.
Returns the length moving average as set by load_cell_set_moving_average().
To calibrate your Load Cell Bricklet you have to
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.
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 default rate is 10Hz and the default gain is 128x.
The following defines are available for this function:
Returns the configuration as set by load_cell_set_configuration().
The following defines are available for this function:
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.
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 send and errors are silently ignored, because they cannot be detected.
See load_cell_set_response_expected() for the list of function ID defines available for this function.
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 and callbacks it is always disabled.
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:
Changes the response expected flag for all setter and callback configuration functions of this device at once.
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.
Registers a callback with ID id to the function callback. The user_data will be given as a parameter of the callback.
The available IDs with corresponding function signatures are listed below.
Sets the period in ms with which the LOAD_CELL_CALLBACK_WEIGHT callback is triggered periodically. A value of 0 turns the callback off.
LOAD_CELL_CALLBACK_WEIGHT is only triggered if the weight has changed since the last triggering.
The default value is 0.
Returns the period as set by load_cell_set_weight_callback_period().
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 default value is ('x', 0, 0).
The following defines are available for this function:
Returns the threshold as set by load_cell_set_weight_callback_threshold().
The following defines are available for this function:
Sets the period in ms with which the threshold callback
is triggered, if the threshold
keeps being reached.
The default value is 100.
Returns the debounce period as set by load_cell_set_debounce_period().
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. 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); } load_cell_register_callback(&load_cell, LOAD_CELL_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.
void callback(uint32_t weight, void *user_data)
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.
LOAD_CELL_CALLBACK_WEIGHT is only triggered if the weight has changed since the last triggering.
void callback(int16_t weight, void *user_data)
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().
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.