C/C++ - Multi Touch Bricklet

This is the description of the C/C++ API bindings for the Multi Touch Bricklet. General information and technical specifications for the Multi Touch 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_multi_touch.h"

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

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

    // Create device object
    MultiTouch mt;
    multi_touch_create(&mt, 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 touch state
    uint16_t state;
    if(multi_touch_get_touch_state(&mt, &state) < 0) {
        fprintf(stderr, "Could not get touch state, probably timeout\n");
        return 1;
    }

    if(state & (1 << 12)) {
        printf("In proximity, ");
    }

    if((state & 0xfff) == 0) {
        printf("No electrodes touched\n");
    } else {
        printf("Electrodes ");
        int i;
        for(i = 0; i < 12; i++) {
            if(state & (1 << i)) {
                printf("%d ", i);
            }
        }
        printf("touched\n");
    }

    printf("Press key to exit\n");
    getchar();
    multi_touch_destroy(&mt);
    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_multi_touch.h"

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

// Callback function for touch state callback
void cb_touch_state(uint16_t state, void *user_data) {
    (void)user_data; // avoid unused parameter warning

    if(state & (1 << 12)) {
        printf("In proximity, ");
    }

    if((state & 0xfff) == 0) {
        printf("No electrodes touched\n");
    } else {
        printf("Electrodes ");
        int i;
        for(i = 0; i < 12; i++) {
            if(state & (1 << i)) {
                printf("%d ", i);
            }
        }
        printf("touched\n");
    }
}

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

    // Create device object
    MultiTouch mt;
    multi_touch_create(&mt, 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 touch state callback to function cb_touch_state
    multi_touch_register_callback(&mt,
                                  MULTI_TOUCH_CALLBACK_TOUCH_STATE,
                                  (void *)cb_touch_state,
                                  NULL);

    printf("Press key to exit\n");
    getchar();
    multi_touch_destroy(&mt);
    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 multi_touch_create(MultiTouch *multi_touch, const char *uid, IPConnection *ipcon)

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

MultiTouch multi_touch;
multi_touch_create(&multi_touch, "YOUR_DEVICE_UID", &ipcon);

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

void multi_touch_destroy(MultiTouch *multi_touch)

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

int multi_touch_get_touch_state(MultiTouch *multi_touch, uint16_t *ret_state)

Returns the current touch state. The state is given as a bitfield.

Bits 0 to 11 represent the 12 electrodes and bit 12 represents the proximity.

If an electrode is touched, the corresponding bit is true. If a hand or similar is in proximity to the electrodes, bit 12 is true.

Example: The state 4103 = 0x1007 = 0b1000000000111 means that electrodes 0, 1 and 2 are touched and that something is in the proximity of the electrodes.

The proximity is activated with a distance of 1-2cm. An electrode is already counted as touched if a finger is nearly touching the electrode. This means that you can put a piece of paper or foil or similar on top of a electrode to build a touch panel with a professional look.

int multi_touch_recalibrate(MultiTouch *multi_touch)

Recalibrates the electrodes. Call this function whenever you changed or moved you electrodes.

int multi_touch_set_electrode_config(MultiTouch *multi_touch, uint16_t enabled_electrodes)

Enables/disables electrodes with a bitfield (see multi_touch_get_touch_state()).

True enables the electrode, false disables the electrode. A disabled electrode will always return false as its state. If you don't need all electrodes you can disable the electrodes that are not needed.

It is recommended that you disable the proximity bit (bit 12) if the proximity feature is not needed. This will reduce the amount of traffic that is produced by the MULTI_TOUCH_CALLBACK_TOUCH_STATE callback.

Disabling electrodes will also reduce power consumption.

Default: 8191 = 0x1FFF = 0b1111111111111 (all electrodes enabled)

int multi_touch_get_electrode_config(MultiTouch *multi_touch, uint16_t *ret_enabled_electrodes)

Returns the electrode configuration, as set by multi_touch_set_electrode_config().

int multi_touch_set_electrode_sensitivity(MultiTouch *multi_touch, uint8_t sensitivity)

Sets the sensitivity of the electrodes. An electrode with a high sensitivity will register a touch earlier then an electrode with a low sensitivity.

If you build a big electrode you might need to decrease the sensitivity, since the area that can be charged will get bigger. If you want to be able to activate an electrode from further away you need to increase the sensitivity.

After a new sensitivity is set, you likely want to call multi_touch_recalibrate() to calibrate the electrodes with the newly defined sensitivity.

The valid sensitivity value range is 5-201.

The default sensitivity value is 181.

int multi_touch_get_electrode_sensitivity(MultiTouch *multi_touch, uint8_t *ret_sensitivity)

Returns the current sensitivity, as set by multi_touch_set_electrode_sensitivity().

Advanced Functions

int multi_touch_get_api_version(MultiTouch *multi_touch, 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 multi_touch_get_response_expected(MultiTouch *multi_touch, 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 multi_touch_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 multi_touch_set_response_expected() for the list of function ID defines available for this function.

int multi_touch_set_response_expected(MultiTouch *multi_touch, 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:

  • MULTI_TOUCH_FUNCTION_RECALIBRATE = 2
  • MULTI_TOUCH_FUNCTION_SET_ELECTRODE_CONFIG = 3
  • MULTI_TOUCH_FUNCTION_SET_ELECTRODE_SENSITIVITY = 6
int multi_touch_set_response_expected_all(MultiTouch *multi_touch, bool response_expected)

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

int multi_touch_get_identity(MultiTouch *multi_touch, 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 multi_touch_register_callback(MultiTouch *multi_touch, 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.

Callbacks

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

multi_touch_register_callback(&multi_touch, MULTI_TOUCH_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.

MULTI_TOUCH_CALLBACK_TOUCH_STATE
void callback(uint16_t state, void *user_data)

Returns the current touch state, see multi_touch_get_touch_state() for information about the state.

This callback is triggered every time the touch state changes.

Constants

MULTI_TOUCH_DEVICE_IDENTIFIER

This constant is used to identify a Multi Touch Bricklet.

The multi_touch_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.

MULTI_TOUCH_DEVICE_DISPLAY_NAME

This constant represents the human readable name of a Multi Touch Bricklet.