MQTT - Piezo Speaker Bricklet

This is the description of the MQTT API bindings for the Piezo Speaker Bricklet. General information and technical specifications for the Piezo Speaker 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).

Beep

Download (example-beep.txt)

1
2
3
4
5
# Change XYZ to the UID of your Piezo Speaker Bricklet

setup:
    # Make 2 second beep with a frequency of 1kHz
    publish '{"duration": 2000, "frequency": 1000}' to tinkerforge/request/piezo_speaker_bricklet/XYZ/beep 

Morse Code

Download (example-morse-code.txt)

1
2
3
4
5
# Change XYZ to the UID of your Piezo Speaker Bricklet

setup:
    # Morse SOS with a frequency of 2kHz
    publish '{"morse": "... --- ...", "frequency": 2000}' to tinkerforge/request/piezo_speaker_bricklet/XYZ/morse_code 

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/piezo_speaker_bricklet/<UID>/beep
Request payload:
  • duration -- int (has symbols)
  • frequency -- int

Beeps with the given frequency for the duration in ms. For example: If you set a duration of 1000, with a frequency value of 2000 the piezo buzzer will beep for one second with a frequency of approximately 2 kHz.

Changed in version 2.0.2 (Plugin): A duration of 0 stops the current beep if any, the frequency parameter is ignored. A duration of 4294967295 results in an infinite beep.

The frequency parameter can be set between 585 and 7100.

The Piezo Speaker Bricklet can only approximate the frequency, it will play the best possible match by applying the calibration (see request/piezo_speaker_bricklet/<UID>/calibrate).

The following symbols are available for this function:

for duration:

  • "Off" = 0
  • "Infinite" = 4294967295
request/piezo_speaker_bricklet/<UID>/morse_code
Request payload:
  • morse -- string
  • frequency -- int

Sets morse code that will be played by the piezo buzzer. The morse code is given as a string consisting of "." (dot), "-" (minus) and " " (space) for dits, dahs and pauses. Every other character is ignored. The second parameter is the frequency (see request/piezo_speaker_bricklet/<UID>/beep).

For example: If you set the string "...---...", the piezo buzzer will beep nine times with the durations "short short short long long long short short short".

The maximum string size is 60.

Advanced Functions

request/piezo_speaker_bricklet/<UID>/calibrate
Response payload:
  • calibration -- bool

The Piezo Speaker Bricklet can play 512 different tones. This function plays each tone and measures the exact frequency back. The result is a mapping between setting value and frequency. This mapping is stored in the EEPROM and loaded on startup.

The Bricklet should come calibrated, you only need to call this function (once) every time you reflash the Bricklet plugin.

Returns true after the calibration finishes.

request/piezo_speaker_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 Piezo Speaker'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/piezo_speaker_bricklet/<UID>/beep_finished
Request payload:
  • register -- bool

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

This callback is triggered if a beep set by request/piezo_speaker_bricklet/<UID>/beep is finished

register/piezo_speaker_bricklet/<UID>/morse_code_finished
Request payload:
  • register -- bool

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

This callback is triggered if the playback of the morse code set by request/piezo_speaker_bricklet/<UID>/morse_code is finished.