Software / API Bindings / MQTT / API Reference and Examples / Bricklets / Multi Touch Bricklet 2.0

MQTT - Multi Touch Bricklet 2.0¶

This is the description of the MQTT API bindings for the Multi Touch Bricklet 2.0. General information and technical specifications for the Multi Touch Bricklet 2.0 are summarized in its hardware description.

An installation guide for the MQTT API bindings is part of their general description.

Examples¶

The example code below is Public Domain (CC0 1.0).

Simple¶

Download (example-simple.txt)

# Change XYZ to the UID of your Multi Touch Bricklet 2.0

setup:
    # Get current touch state
    subscribe to tinkerforge/response/multi_touch_v2_bricklet/XYZ/get_touch_state
    publish '' to tinkerforge/request/multi_touch_v2_bricklet/XYZ/get_touch_state

Callback¶

Download (example-callback.txt)

# Change XYZ to the UID of your Multi Touch Bricklet 2.0

setup:
    # Handle incoming touch state callbacks
    subscribe to tinkerforge/callback/multi_touch_v2_bricklet/XYZ/touch_state
    publish '{"register": true}' to tinkerforge/register/multi_touch_v2_bricklet/XYZ/touch_state # Register touch_state callback

    # Set period for touch state callback to 0.01s (10ms)
    publish '{"period": 10, "value_has_to_change": true}' to tinkerforge/request/multi_touch_v2_bricklet/XYZ/set_touch_state_callback_configuration

API¶

All published payloads to and from the MQTT bindings are in JSON format.

If an error occures, the bindings publish a JSON object containing the error message as member _ERROR. It is published on the corresponding response topic: .../response/... for .../request/... and .../callback/... for .../register/....

Basic Functions¶

request/multi_touch_v2_bricklet/<UID>/get_touch_state¶

Request:	empty payload
Response:	state – Type: [bool, ...], Length: 13

Returns the current touch state. The state is given as a array of bools.

Element 0 to 11 represent the 12 electrodes and element 12 represents the proximity.

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

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.

If you want to get the value periodically, it is recommended to use the register/multi_touch_v2_bricklet/<UID>/touch_state callback. You can set the callback configuration with request/multi_touch_v2_bricklet/<UID>/set_touch_state_callback_configuration.

request/multi_touch_v2_bricklet/<UID>/recalibrate¶

Request:	empty payload
Response:	no response

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

request/multi_touch_v2_bricklet/<UID>/set_electrode_config¶

Request:	enabled_electrodes – Type: [bool, ...], Length: 13, Default: [true,true,true,true,true,true,true,true,true,true,true,true,true]
Response:	no response

Enables/disables electrodes with a bool array (see request/multi_touch_v2_bricklet/<UID>/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 electrode (element 12) if the proximity feature is not needed. This will reduce the amount of traffic that is produced by the register/multi_touch_v2_bricklet/<UID>/touch_state callback.

Disabling electrodes will also reduce power consumption.

request/multi_touch_v2_bricklet/<UID>/get_electrode_config¶

Request:	empty payload
Response:	enabled_electrodes – Type: [bool, ...], Length: 13, Default: [true,true,true,true,true,true,true,true,true,true,true,true,true]

Returns the electrode configuration, as set by request/multi_touch_v2_bricklet/<UID>/set_electrode_config.

request/multi_touch_v2_bricklet/<UID>/set_electrode_sensitivity¶

Request:	sensitivity – Type: int, Range: [5 to 201], Default: 181
Response:	no response

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 request/multi_touch_v2_bricklet/<UID>/recalibrate to calibrate the electrodes with the newly defined sensitivity.

request/multi_touch_v2_bricklet/<UID>/get_electrode_sensitivity¶

Request:	empty payload
Response:	sensitivity – Type: int, Range: [5 to 201], Default: 181

Returns the current sensitivity, as set by request/multi_touch_v2_bricklet/<UID>/set_electrode_sensitivity.

request/multi_touch_v2_bricklet/<UID>/set_touch_led_config¶

Request:	config – Type: int, Range: See symbols, Default: 3
Response:	no response

Configures the touch LED to be either turned off, turned on, blink in heartbeat mode or show the touch state (electrode touched = LED on).

The following symbols are available for this function:

For config:

"off" = 0
"on" = 1
"show_heartbeat" = 2
"show_touch" = 3

request/multi_touch_v2_bricklet/<UID>/get_touch_led_config¶

Request:	empty payload
Response:	config – Type: int, Range: See symbols, Default: 3

Returns the LED configuration as set by request/multi_touch_v2_bricklet/<UID>/set_touch_led_config

The following symbols are available for this function:

For config:

"off" = 0
"on" = 1
"show_heartbeat" = 2
"show_touch" = 3

Advanced Functions¶

request/multi_touch_v2_bricklet/<UID>/get_spitfp_error_count¶

Request:	empty payload
Response:	error_count_ack_checksum – Type: int, Range: [0 to 2³² - 1] error_count_message_checksum – Type: int, Range: [0 to 2³² - 1] error_count_frame – Type: int, Range: [0 to 2³² - 1] error_count_overflow – Type: int, Range: [0 to 2³² - 1]

Returns the error count for the communication between Brick and Bricklet.

The errors are divided into

ACK checksum errors,
message checksum errors,
framing errors and
overflow errors.

The errors counts are for errors that occur on the Bricklet side. All Bricks have a similar function that returns the errors on the Brick side.

request/multi_touch_v2_bricklet/<UID>/set_status_led_config¶

Request:	config – Type: int, Range: See symbols, Default: 3
Response:	no response

Sets the status LED configuration. By default the LED shows communication traffic between Brick and Bricklet, it flickers once for every 10 received data packets.

You can also turn the LED permanently on/off or show a heartbeat.

If the Bricklet is in bootloader mode, the LED is will show heartbeat by default.

The following symbols are available for this function:

For config:

"off" = 0
"on" = 1
"show_heartbeat" = 2
"show_status" = 3

request/multi_touch_v2_bricklet/<UID>/get_status_led_config¶

Request:	empty payload
Response:	config – Type: int, Range: See symbols, Default: 3

Returns the configuration as set by request/multi_touch_v2_bricklet/<UID>/set_status_led_config

The following symbols are available for this function:

For config:

"off" = 0
"on" = 1
"show_heartbeat" = 2
"show_status" = 3

request/multi_touch_v2_bricklet/<UID>/get_chip_temperature¶

Request:	empty payload
Response:	temperature – Type: int, Unit: 1 °C, Range: [-2¹⁵ to 2¹⁵ - 1]

Returns the temperature as measured inside the microcontroller. The value returned is not the ambient temperature!

The temperature is only proportional to the real temperature and it has bad accuracy. Practically it is only useful as an indicator for temperature changes.

request/multi_touch_v2_bricklet/<UID>/reset¶

Request:	empty payload
Response:	no response

Calling this function will reset the Bricklet. All configurations will be lost.

After a reset you have to create new device objects, calling functions on the existing ones will result in undefined behavior!

request/multi_touch_v2_bricklet/<UID>/get_identity¶

Request:

empty payload

Response:

uid – Type: string, Length: up to 8
connected_uid – Type: string, Length: up to 8
position – Type: char, Range: ["a" to "h", "z"]
hardware_version – Type: [int, ...], Length: 3

0: major – Type: int, Range: [0 to 255]
1: minor – Type: int, Range: [0 to 255]
2: revision – Type: int, Range: [0 to 255]

firmware_version – Type: [int, ...], Length: 3

0: major – Type: int, Range: [0 to 255]
1: minor – Type: int, Range: [0 to 255]
2: revision – Type: int, Range: [0 to 255]

device_identifier – Type: int, Range: [0 to 2¹⁶ - 1]
_display_name – Type: string

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 at position 'z'.

The device identifier numbers can be found here. If symbolic output is not disabled, the device identifier is mapped to the corresponding name in the format used in topics.

The display name contains the Multi Touch 2.0's name in a human readable form.

Callback Configuration Functions¶

request/multi_touch_v2_bricklet/<UID>/set_touch_state_callback_configuration¶

Request:	period – Type: int, Unit: 1 ms, Range: [0 to 2³² - 1], Default: 0 value_has_to_change – Type: bool, Default: false
Response:	no response

The period is the period with which the register/multi_touch_v2_bricklet/<UID>/touch_state callback is triggered periodically. A value of 0 turns the callback off.

If the value has to change-parameter is set to true, the callback is only triggered after the value has changed. If the value didn't change within the period, the callback is triggered immediately on change.

If it is set to false, the callback is continuously triggered with the period, independent of the value.

request/multi_touch_v2_bricklet/<UID>/get_touch_state_callback_configuration¶

Request:	empty payload
Response:	period – Type: int, Unit: 1 ms, Range: [0 to 2³² - 1], Default: 0 value_has_to_change – Type: bool, Default: false

Returns the callback configuration as set by request/multi_touch_v2_bricklet/<UID>/set_touch_state_callback_configuration.

Callbacks¶

Callbacks can be registered to receive time critical or recurring data from the device. The registration is done with the corresponding .../register/... topic and an optional suffix. This suffix can be used to deregister the callback later.

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.

register/multi_touch_v2_bricklet/<UID>/touch_state¶

Register Request:	register – Type: bool
Callback Response:	state – Type: [bool, ...], Length: 13

A callback can be registered for this event by publishing to the .../register/multi_touch_v2_bricklet/<UID>/touch_state[/<SUFFIX>] topic with the payload "true". An added callback can be removed by publishing to the same topic with the payload "false". To support multiple (de)registrations, e.g. for message filtering, an optional suffix can be used.

If the callback is triggered, a message with it's payload is published under the corresponding .../callback/multi_touch_v2_bricklet/<UID>/touch_state[/<SUFFIX>] topic for each registered suffix.

Returns the current touch state, see request/multi_touch_v2_bricklet/<UID>/get_touch_state for information about the state.

This callback is triggered every time the touch state changes with a given period (see request/multi_touch_v2_bricklet/<UID>/set_touch_state_callback_configuration)

Internal Functions¶

Internal functions are used for maintenance tasks such as flashing a new firmware of changing the UID of a Bricklet. These task should be performed using Brick Viewer instead of using the internal functions directly.

request/multi_touch_v2_bricklet/<UID>/set_bootloader_mode¶

Request:	mode – Type: int, Range: See symbols
Response:	status – Type: int, Range: See symbols

Sets the bootloader mode and returns the status after the requested mode change was instigated.

You can change from bootloader mode to firmware mode and vice versa. A change from bootloader mode to firmware mode will only take place if the entry function, device identifier and CRC are present and correct.

This function is used by Brick Viewer during flashing. It should not be necessary to call it in a normal user program.

The following symbols are available for this function:

For mode:

"bootloader" = 0
"firmware" = 1
"bootloader_wait_for_reboot" = 2
"firmware_wait_for_reboot" = 3
"firmware_wait_for_erase_and_reboot" = 4

For status:

"ok" = 0
"invalid_mode" = 1
"no_change" = 2
"entry_function_not_present" = 3
"device_identifier_incorrect" = 4
"crc_mismatch" = 5

request/multi_touch_v2_bricklet/<UID>/get_bootloader_mode¶

Request:	empty payload
Response:	mode – Type: int, Range: See symbols

Returns the current bootloader mode, see request/multi_touch_v2_bricklet/<UID>/set_bootloader_mode.

The following symbols are available for this function:

For mode:

"bootloader" = 0
"firmware" = 1
"bootloader_wait_for_reboot" = 2
"firmware_wait_for_reboot" = 3
"firmware_wait_for_erase_and_reboot" = 4

request/multi_touch_v2_bricklet/<UID>/set_write_firmware_pointer¶

Request:	pointer – Type: int, Unit: 1 B, Range: [0 to 2³² - 1]
Response:	no response

Sets the firmware pointer for request/multi_touch_v2_bricklet/<UID>/write_firmware. The pointer has to be increased by chunks of size 64. The data is written to flash every 4 chunks (which equals to one page of size 256).

This function is used by Brick Viewer during flashing. It should not be necessary to call it in a normal user program.

request/multi_touch_v2_bricklet/<UID>/write_firmware¶

Request:	data – Type: [int, ...], Length: 64, Range: [0 to 255]
Response:	status – Type: int, Range: [0 to 255]

Writes 64 Bytes of firmware at the position as written by request/multi_touch_v2_bricklet/<UID>/set_write_firmware_pointer before. The firmware is written to flash every 4 chunks.

You can only write firmware in bootloader mode.

This function is used by Brick Viewer during flashing. It should not be necessary to call it in a normal user program.

request/multi_touch_v2_bricklet/<UID>/write_uid¶

Request:	uid – Type: int, Range: [0 to 2³² - 1]
Response:	no response

Writes a new UID into flash. If you want to set a new UID you have to decode the Base58 encoded UID string into an integer first.

We recommend that you use Brick Viewer to change the UID.

request/multi_touch_v2_bricklet/<UID>/read_uid¶

Request:	empty payload
Response:	uid – Type: int, Range: [0 to 2³² - 1]

Returns the current UID as an integer. Encode as Base58 to get the usual string version.