C/C++ - Linear Poti Bricklet

This is the description of the C/C++ API bindings for the Linear Poti Bricklet. General information and technical specifications for the Linear Poti 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_linear_poti.h"

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

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

    // Create device object
    LinearPoti lp;
    linear_poti_create(&lp, 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 position
    uint16_t position;
    if(linear_poti_get_position(&lp, &position) < 0) {
        fprintf(stderr, "Could not get position, probably timeout\n");
        return 1;
    }

    printf("Position: %u\n", position); // Range: 0 to 100

    printf("Press key to exit\n");
    getchar();
    linear_poti_destroy(&lp);
    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_linear_poti.h"

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

// Callback function for position callback
void cb_position(uint16_t position, void *user_data) {
    (void)user_data; // avoid unused parameter warning

    printf("Position: %u\n", position); // Range: 0 to 100
}

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

    // Create device object
    LinearPoti lp;
    linear_poti_create(&lp, 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 position callback to function cb_position
    linear_poti_register_callback(&lp,
                                  LINEAR_POTI_CALLBACK_POSITION,
                                  (void *)cb_position,
                                  NULL);

    // Set period for position callback to 0.05s (50ms)
    // Note: The position callback is only called every 0.05 seconds
    //       if the position has changed since the last call!
    linear_poti_set_position_callback_period(&lp, 50);

    printf("Press key to exit\n");
    getchar();
    linear_poti_destroy(&lp);
    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 linear_poti_create(LinearPoti *linear_poti, const char *uid, IPConnection *ipcon)

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

LinearPoti linear_poti;
linear_poti_create(&linear_poti, "YOUR_DEVICE_UID", &ipcon);

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

void linear_poti_destroy(LinearPoti *linear_poti)

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

int linear_poti_get_position(LinearPoti *linear_poti, uint16_t *ret_position)

Returns the position of the linear potentiometer. The value is between 0 (slider down) and 100 (slider up).

If you want to get the position periodically, it is recommended to use the LINEAR_POTI_CALLBACK_POSITION callback and set the period with linear_poti_set_position_callback_period().

Advanced Functions

int linear_poti_get_analog_value(LinearPoti *linear_poti, uint16_t *ret_value)

Returns the value as read by a 12-bit analog-to-digital converter. The value is between 0 and 4095.

Note

The value returned by linear_poti_get_position() is averaged over several samples to yield less noise, while linear_poti_get_analog_value() gives back raw unfiltered analog values. The only reason to use linear_poti_get_analog_value() is, if you need the full resolution of the analog-to-digital converter.

If you want the analog value periodically, it is recommended to use the LINEAR_POTI_CALLBACK_ANALOG_VALUE callback and set the period with linear_poti_set_analog_value_callback_period().

int linear_poti_get_api_version(LinearPoti *linear_poti, 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 linear_poti_get_response_expected(LinearPoti *linear_poti, 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 linear_poti_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 linear_poti_set_response_expected() for the list of function ID defines available for this function.

int linear_poti_set_response_expected(LinearPoti *linear_poti, 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:

  • LINEAR_POTI_FUNCTION_SET_POSITION_CALLBACK_PERIOD = 3
  • LINEAR_POTI_FUNCTION_SET_ANALOG_VALUE_CALLBACK_PERIOD = 5
  • LINEAR_POTI_FUNCTION_SET_POSITION_CALLBACK_THRESHOLD = 7
  • LINEAR_POTI_FUNCTION_SET_ANALOG_VALUE_CALLBACK_THRESHOLD = 9
  • LINEAR_POTI_FUNCTION_SET_DEBOUNCE_PERIOD = 11
int linear_poti_set_response_expected_all(LinearPoti *linear_poti, bool response_expected)

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

int linear_poti_get_identity(LinearPoti *linear_poti, 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 linear_poti_register_callback(LinearPoti *linear_poti, 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 linear_poti_set_position_callback_period(LinearPoti *linear_poti, uint32_t period)

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

The LINEAR_POTI_CALLBACK_POSITION callback is only triggered if the position has changed since the last triggering.

The default value is 0.

int linear_poti_get_position_callback_period(LinearPoti *linear_poti, uint32_t *ret_period)

Returns the period as set by linear_poti_set_position_callback_period().

int linear_poti_set_analog_value_callback_period(LinearPoti *linear_poti, uint32_t period)

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

The LINEAR_POTI_CALLBACK_ANALOG_VALUE callback is only triggered if the analog value has changed since the last triggering.

The default value is 0.

int linear_poti_get_analog_value_callback_period(LinearPoti *linear_poti, uint32_t *ret_period)

Returns the period as set by linear_poti_set_analog_value_callback_period().

int linear_poti_set_position_callback_threshold(LinearPoti *linear_poti, char option, uint16_t min, uint16_t max)

Sets the thresholds for the LINEAR_POTI_CALLBACK_POSITION_REACHED callback.

The following options are possible:

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

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

The following defines are available for this function:

  • LINEAR_POTI_THRESHOLD_OPTION_OFF = 'x'
  • LINEAR_POTI_THRESHOLD_OPTION_OUTSIDE = 'o'
  • LINEAR_POTI_THRESHOLD_OPTION_INSIDE = 'i'
  • LINEAR_POTI_THRESHOLD_OPTION_SMALLER = '<'
  • LINEAR_POTI_THRESHOLD_OPTION_GREATER = '>'
int linear_poti_get_position_callback_threshold(LinearPoti *linear_poti, char *ret_option, uint16_t *ret_min, uint16_t *ret_max)

Returns the threshold as set by linear_poti_set_position_callback_threshold().

The following defines are available for this function:

  • LINEAR_POTI_THRESHOLD_OPTION_OFF = 'x'
  • LINEAR_POTI_THRESHOLD_OPTION_OUTSIDE = 'o'
  • LINEAR_POTI_THRESHOLD_OPTION_INSIDE = 'i'
  • LINEAR_POTI_THRESHOLD_OPTION_SMALLER = '<'
  • LINEAR_POTI_THRESHOLD_OPTION_GREATER = '>'
int linear_poti_set_analog_value_callback_threshold(LinearPoti *linear_poti, char option, uint16_t min, uint16_t max)

Sets the thresholds for the LINEAR_POTI_CALLBACK_ANALOG_VALUE_REACHED callback.

The following options are possible:

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

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

The following defines are available for this function:

  • LINEAR_POTI_THRESHOLD_OPTION_OFF = 'x'
  • LINEAR_POTI_THRESHOLD_OPTION_OUTSIDE = 'o'
  • LINEAR_POTI_THRESHOLD_OPTION_INSIDE = 'i'
  • LINEAR_POTI_THRESHOLD_OPTION_SMALLER = '<'
  • LINEAR_POTI_THRESHOLD_OPTION_GREATER = '>'
int linear_poti_get_analog_value_callback_threshold(LinearPoti *linear_poti, char *ret_option, uint16_t *ret_min, uint16_t *ret_max)

Returns the threshold as set by linear_poti_set_analog_value_callback_threshold().

The following defines are available for this function:

  • LINEAR_POTI_THRESHOLD_OPTION_OFF = 'x'
  • LINEAR_POTI_THRESHOLD_OPTION_OUTSIDE = 'o'
  • LINEAR_POTI_THRESHOLD_OPTION_INSIDE = 'i'
  • LINEAR_POTI_THRESHOLD_OPTION_SMALLER = '<'
  • LINEAR_POTI_THRESHOLD_OPTION_GREATER = '>'
int linear_poti_set_debounce_period(LinearPoti *linear_poti, 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 linear_poti_get_debounce_period(LinearPoti *linear_poti, uint32_t *ret_debounce)

Returns the debounce period as set by linear_poti_set_debounce_period().

Callbacks

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

linear_poti_register_callback(&linear_poti, LINEAR_POTI_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.

LINEAR_POTI_CALLBACK_POSITION
void callback(uint16_t position, void *user_data)

This callback is triggered periodically with the period that is set by linear_poti_set_position_callback_period(). The parameter is the position of the linear potentiometer.

The LINEAR_POTI_CALLBACK_POSITION callback is only triggered if the position has changed since the last triggering.

LINEAR_POTI_CALLBACK_ANALOG_VALUE
void callback(uint16_t value, void *user_data)

This callback is triggered periodically with the period that is set by linear_poti_set_analog_value_callback_period(). The parameter is the analog value of the Linear Potentiometer.

The LINEAR_POTI_CALLBACK_ANALOG_VALUE callback is only triggered if the position has changed since the last triggering.

LINEAR_POTI_CALLBACK_POSITION_REACHED
void callback(uint16_t position, void *user_data)

This callback is triggered when the threshold as set by linear_poti_set_position_callback_threshold() is reached. The parameter is the position of the linear potentiometer.

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

LINEAR_POTI_CALLBACK_ANALOG_VALUE_REACHED
void callback(uint16_t value, void *user_data)

This callback is triggered when the threshold as set by linear_poti_set_analog_value_callback_threshold() is reached. The parameter is the analog value of the linear potentiometer.

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

Constants

LINEAR_POTI_DEVICE_IDENTIFIER

This constant is used to identify a Linear Poti Bricklet.

The linear_poti_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.

LINEAR_POTI_DEVICE_DISPLAY_NAME

This constant represents the human readable name of a Linear Poti Bricklet.