MQTT - RGB LED Matrix Bricklet

This is the description of the MQTT API bindings for the RGB LED Matrix Bricklet. General information and technical specifications for the RGB LED Matrix Bricklet 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).

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 attribute "_ERROR". It is published on the corresponding response topic: .../response/... for .../request/... and .../callback/... for .../register/....

Basic Functions

request/rgb_led_matrix_bricklet/<UID>/set_red
Request payload:
  • red -- [int,... (x64)]

Sets the 64 red LED values of the matrix.

request/rgb_led_matrix_bricklet/<UID>/get_red
Response payload:
  • red -- [int,... (x64)]

Returns the red LED values as set by request/rgb_led_matrix_bricklet/<UID>/set_red.

request/rgb_led_matrix_bricklet/<UID>/set_green
Request payload:
  • green -- [int,... (x64)]

Sets the 64 green LED values of the matrix.

request/rgb_led_matrix_bricklet/<UID>/get_green
Response payload:
  • green -- [int,... (x64)]

Returns the green LED values as set by request/rgb_led_matrix_bricklet/<UID>/set_green.

request/rgb_led_matrix_bricklet/<UID>/set_blue
Request payload:
  • blue -- [int,... (x64)]

Sets the 64 blue LED values of the matrix.

request/rgb_led_matrix_bricklet/<UID>/get_blue
Response payload:
  • blue -- [int,... (x64)]

Returns the blue LED values as set by request/rgb_led_matrix_bricklet/<UID>/set_blue.

request/rgb_led_matrix_bricklet/<UID>/set_frame_duration
Request payload:
  • frame_duration -- int

Sets the frame duration in ms.

Example: If you want to achieve 20 frames per second, you should set the frame duration to 50ms (50ms * 20 = 1 second).

Set this value to 0 to turn the automatic frame write mechanism off.

Approach:

For frame duration of 0 see request/rgb_led_matrix_bricklet/<UID>/draw_frame.

Default value: 0 = off.

request/rgb_led_matrix_bricklet/<UID>/get_frame_duration
Response payload:
  • frame_duration -- int

Returns the frame duration in ms as set by request/rgb_led_matrix_bricklet/<UID>/set_frame_duration.

request/rgb_led_matrix_bricklet/<UID>/draw_frame

If you set the frame duration to 0 (see request/rgb_led_matrix_bricklet/<UID>/set_frame_duration), you can use this function to transfer the frame to the matrix.

Approach:

Advanced Functions

request/rgb_led_matrix_bricklet/<UID>/get_supply_voltage
Response payload:
  • voltage -- int

Returns the current supply voltage of the Bricklet. The voltage is given in mV.

request/rgb_led_matrix_bricklet/<UID>/get_spitfp_error_count
Response payload:
  • error_count_ack_checksum -- int
  • error_count_message_checksum -- int
  • error_count_frame -- int
  • error_count_overflow -- int

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/rgb_led_matrix_bricklet/<UID>/set_bootloader_mode
Request payload:
  • mode -- int (has symbols)
Response payload:
  • status -- int (has 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
  • "BootloaderWaitForReboot" = 2
  • "FirmwareWaitForReboot" = 3
  • "FirmwareWaitForEraseAndReboot" = 4

for status:

  • "OK" = 0
  • "InvalidMode" = 1
  • "NoChange" = 2
  • "EntryFunctionNotPresent" = 3
  • "DeviceIdentifierIncorrect" = 4
  • "CRCMismatch" = 5
request/rgb_led_matrix_bricklet/<UID>/get_bootloader_mode
Response payload:
  • mode -- int (has symbols)

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

The following symbols are available for this function:

for mode:

  • "Bootloader" = 0
  • "Firmware" = 1
  • "BootloaderWaitForReboot" = 2
  • "FirmwareWaitForReboot" = 3
  • "FirmwareWaitForEraseAndReboot" = 4
request/rgb_led_matrix_bricklet/<UID>/set_write_firmware_pointer
Request payload:
  • pointer -- int

Sets the firmware pointer for request/rgb_led_matrix_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/rgb_led_matrix_bricklet/<UID>/write_firmware
Request payload:
  • data -- [int,... (x64)]
Response payload:
  • status -- int

Writes 64 Bytes of firmware at the position as written by request/rgb_led_matrix_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/rgb_led_matrix_bricklet/<UID>/set_status_led_config
Request payload:
  • config -- int (has symbols)

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
  • "ShowHeartbeat" = 2
  • "ShowStatus" = 3
request/rgb_led_matrix_bricklet/<UID>/get_status_led_config
Response payload:
  • config -- int (has symbols)

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

The following symbols are available for this function:

for config:

  • "Off" = 0
  • "On" = 1
  • "ShowHeartbeat" = 2
  • "ShowStatus" = 3
request/rgb_led_matrix_bricklet/<UID>/get_chip_temperature
Response payload:
  • temperature -- int

Returns the temperature in °C 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/rgb_led_matrix_bricklet/<UID>/reset

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/rgb_led_matrix_bricklet/<UID>/write_uid
Request payload:
  • uid -- int

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/rgb_led_matrix_bricklet/<UID>/read_uid
Response payload:
  • uid -- int

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

request/rgb_led_matrix_bricklet/<UID>/get_identity
Response payload:
  • uid -- string
  • connected_uid -- string
  • position -- char
  • hardware_version -- [int,int,int]
  • firmware_version -- [int,int,int]
  • device_identifier -- int (has symbols)
  • _display_name -- 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' or 'd'.

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 RGB LED Matrix's name in a human readable form.

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/rgb_led_matrix_bricklet/<UID>/frame_started
Request payload:
  • register -- bool
Response payload:
  • frame_number -- int

A callback can be registered for this event by publishing to the .../register/rgb_led_matrix_bricklet/<UID>/frame_started[/<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/rgb_led_matrix_bricklet/<UID>/frame_started[/<SUFFIX>] topic for each registered suffix.

This callback is triggered as soon as a new frame write is started. The LED values are double buffered, so you can send the LED values for the next frame directly after this callback is triggered.