C/C++ - Hall Effect Bricklet

This is the description of the C/C++ API bindings for the Hall Effect Bricklet. General information and technical specifications for the Hall Effect 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_hall_effect.h"

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

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

    // Create device object
    HallEffect he;
    hall_effect_create(&he, 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 edge count without reset
    uint32_t count;
    if(hall_effect_get_edge_count(&he, false, &count) < 0) {
        fprintf(stderr, "Could not get edge count without reset, probably timeout\n");
        return 1;
    }

    printf("Count: %u\n", count);

    printf("Press key to exit\n");
    getchar();
    hall_effect_destroy(&he);
    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_hall_effect.h"

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

// Callback function for edge count callback
void cb_edge_count(uint32_t count, bool value, void *user_data) {
    (void)value; (void)user_data; // avoid unused parameter warning

    printf("Count: %u\n", count);
}

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

    // Create device object
    HallEffect he;
    hall_effect_create(&he, 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 edge count callback to function cb_edge_count
    hall_effect_register_callback(&he,
                                  HALL_EFFECT_CALLBACK_EDGE_COUNT,
                                  (void *)cb_edge_count,
                                  NULL);

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

    printf("Press key to exit\n");
    getchar();
    hall_effect_destroy(&he);
    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 hall_effect_create(HallEffect *hall_effect, const char *uid, IPConnection *ipcon)

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

HallEffect hall_effect;
hall_effect_create(&hall_effect, "YOUR_DEVICE_UID", &ipcon);

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

void hall_effect_destroy(HallEffect *hall_effect)

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

int hall_effect_get_value(HallEffect *hall_effect, bool *ret_value)

Returns true if a magnetic field of 35 Gauss (3.5mT) or greater is detected.

int hall_effect_get_edge_count(HallEffect *hall_effect, bool reset_counter, uint32_t *ret_count)

Returns the current value of the edge counter. You can configure edge type (rising, falling, both) that is counted with hall_effect_set_edge_count_config().

If you set the reset counter to true, the count is set back to 0 directly after it is read.

Advanced Functions

int hall_effect_set_edge_count_config(HallEffect *hall_effect, uint8_t edge_type, uint8_t debounce)

The edge type parameter configures if rising edges, falling edges or both are counted. Possible edge types are:

  • 0 = rising (default)
  • 1 = falling
  • 2 = both

A magnetic field of 35 Gauss (3.5mT) or greater causes a falling edge and a magnetic field of 25 Gauss (2.5mT) or smaller causes a rising edge.

If a magnet comes near the Bricklet the signal goes low (falling edge), if a magnet is removed from the vicinity the signal goes high (rising edge).

The debounce time is given in ms.

Configuring an edge counter resets its value to 0.

If you don't know what any of this means, just leave it at default. The default configuration is very likely OK for you.

Default values: 0 (edge type) and 100ms (debounce time)

The following defines are available for this function:

  • HALL_EFFECT_EDGE_TYPE_RISING = 0
  • HALL_EFFECT_EDGE_TYPE_FALLING = 1
  • HALL_EFFECT_EDGE_TYPE_BOTH = 2
int hall_effect_get_edge_count_config(HallEffect *hall_effect, uint8_t *ret_edge_type, uint8_t *ret_debounce)

Returns the edge type and debounce time as set by hall_effect_set_edge_count_config().

The following defines are available for this function:

  • HALL_EFFECT_EDGE_TYPE_RISING = 0
  • HALL_EFFECT_EDGE_TYPE_FALLING = 1
  • HALL_EFFECT_EDGE_TYPE_BOTH = 2
int hall_effect_get_api_version(HallEffect *hall_effect, 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 hall_effect_get_response_expected(HallEffect *hall_effect, 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 hall_effect_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 hall_effect_set_response_expected() for the list of function ID defines available for this function.

int hall_effect_set_response_expected(HallEffect *hall_effect, 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:

  • HALL_EFFECT_FUNCTION_SET_EDGE_COUNT_CONFIG = 3
  • HALL_EFFECT_FUNCTION_SET_EDGE_INTERRUPT = 5
  • HALL_EFFECT_FUNCTION_SET_EDGE_COUNT_CALLBACK_PERIOD = 7
int hall_effect_set_response_expected_all(HallEffect *hall_effect, bool response_expected)

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

int hall_effect_get_identity(HallEffect *hall_effect, 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 hall_effect_register_callback(HallEffect *hall_effect, 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 hall_effect_set_edge_interrupt(HallEffect *hall_effect, uint32_t edges)

Sets the number of edges until an interrupt is invoked.

If edges is set to n, an interrupt is invoked for every n-th detected edge.

If edges is set to 0, the interrupt is disabled.

Default value is 0.

int hall_effect_get_edge_interrupt(HallEffect *hall_effect, uint32_t *ret_edges)

Returns the edges as set by hall_effect_set_edge_interrupt().

int hall_effect_set_edge_count_callback_period(HallEffect *hall_effect, uint32_t period)

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

The HALL_EFFECT_CALLBACK_EDGE_COUNT callback is only triggered if the edge count has changed since the last triggering.

The default value is 0.

int hall_effect_get_edge_count_callback_period(HallEffect *hall_effect, uint32_t *ret_period)

Returns the period as set by hall_effect_set_edge_count_callback_period().

Callbacks

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

hall_effect_register_callback(&hall_effect, HALL_EFFECT_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.

HALL_EFFECT_CALLBACK_EDGE_COUNT
void callback(uint32_t count, bool value, void *user_data)

This callback is triggered periodically with the period that is set by hall_effect_set_edge_count_callback_period(). The parameters are the current count and the current value (see hall_effect_get_value() and hall_effect_get_edge_count()).

The HALL_EFFECT_CALLBACK_EDGE_COUNT callback is only triggered if the count or value changed since the last triggering.

Constants

HALL_EFFECT_DEVICE_IDENTIFIER

This constant is used to identify a Hall Effect Bricklet.

The hall_effect_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.

HALL_EFFECT_DEVICE_DISPLAY_NAME

This constant represents the human readable name of a Hall Effect Bricklet.