Software / API Bindings / MQTT / API Reference and Examples / Bricklets / Sound Pressure Level Bricklet

MQTT - Sound Pressure Level Bricklet¶

This is the description of the MQTT API bindings for the Sound Pressure Level Bricklet. General information and technical specifications for the Sound Pressure Level 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).

Simple¶

Download (example-simple.txt)

# Change XYZ to the UID of your Sound Pressure Level Bricklet

setup:
    # Get current decibel
    subscribe to tinkerforge/response/sound_pressure_level_bricklet/XYZ/get_decibel
    publish '' to tinkerforge/request/sound_pressure_level_bricklet/XYZ/get_decibel

Callback¶

Download (example-callback.txt)

# Change XYZ to the UID of your Sound Pressure Level Bricklet

setup:
    # Handle incoming decibel callbacks
    subscribe to tinkerforge/callback/sound_pressure_level_bricklet/XYZ/decibel
    publish '{"register": true}' to tinkerforge/register/sound_pressure_level_bricklet/XYZ/decibel # Register decibel callback

    # Set period for decibel callback to 1s (1000ms) without a threshold
    publish '{"period": 1000, "value_has_to_change": false, "option": "off", "min": 0, "max": 0}' to tinkerforge/request/sound_pressure_level_bricklet/XYZ/set_decibel_callback_configuration

Threshold¶

Download (example-threshold.txt)

# Change XYZ to the UID of your Sound Pressure Level Bricklet

setup:
    # Handle incoming decibel callbacks
    subscribe to tinkerforge/callback/sound_pressure_level_bricklet/XYZ/decibel
    publish '{"register": true}' to tinkerforge/register/sound_pressure_level_bricklet/XYZ/decibel # Register decibel callback

    # Configure threshold for decibel "greater than 60 dB(A)"
    # with a debounce period of 1s (1000ms)
    publish '{"period": 1000, "value_has_to_change": false, "option": "greater", "min": 600, "max": 0}' to tinkerforge/request/sound_pressure_level_bricklet/XYZ/set_decibel_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/sound_pressure_level_bricklet/<UID>/get_decibel¶

Request:	empty payload
Response:	decibel – Type: int, Unit: 1/10 dB, Range: [0 to 120]

Returns the measured sound pressure in decibels.

The Bricklet supports the weighting standards dB(A), dB(B), dB(C), dB(D), dB(Z) and ITU-R 468. You can configure the weighting with request/sound_pressure_level_bricklet/<UID>/set_configuration.

By default dB(A) will be used.

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

request/sound_pressure_level_bricklet/<UID>/get_spectrum¶

Request:	empty payload
Response:	spectrum – Type: [int, ...], Length: variable, Unit: ? dB, Range: [0 to 2¹⁶ - 1]

Returns the frequency spectrum. The length of the spectrum is between 512 (FFT size 1024) and 64 (FFT size 128). See request/sound_pressure_level_bricklet/<UID>/set_configuration.

Each array element is one bin of the FFT. The first bin is always the DC offset and the other bins have a size between 40Hz (FFT size 1024) and 320Hz (FFT size 128).

In sum the frequency of the spectrum always has a range from 0 to 20480Hz (the FFT is applied to samples with a frequency of 40960Hz).

The returned data is already equalized, which means that the microphone frequency response is compensated and the weighting function is applied (see request/sound_pressure_level_bricklet/<UID>/set_configuration for the available weighting standards). Use dB(Z) if you need the unaltered spectrum.

The values are not in dB form yet. If you want a proper dB scale of the spectrum you have to apply the formula f(x) = 20*log10(max(1, x/sqrt(2))) on each value.

request/sound_pressure_level_bricklet/<UID>/set_configuration¶

Request:	fft_size – Type: int, Range: See symbols, Default: 3 weighting – Type: int, Range: See symbols, Default: 0
Response:	no response

Sets the Sound Pressure Level Bricklet configuration.

With different FFT sizes the Bricklet has a different amount of samples per second and the size of the FFT bins changes. The higher the FFT size the more precise is the result of the dB(X) calculation.

Available FFT sizes are:

1024: 512 bins, 10 samples per second, each bin has size 40Hz
512: 256 bins, 20 samples per second, each bin has size 80Hz
256: 128 bins, 40 samples per second, each bin has size 160Hz
128: 64 bins, 80 samples per second, each bin has size 320Hz

The Bricklet supports different weighting functions. You can choose between dB(A), dB(B), dB(C), dB(D), dB(Z) and ITU-R 468.

dB(A/B/C/D) are the standard dB weighting curves. dB(A) is often used to measure volumes at concerts etc. dB(Z) has a flat response, no weighting is applied. ITU-R 468 is an ITU weighting standard mostly used in the UK and Europe.

The following symbols are available for this function:

For fft_size:

"128" = 0
"256" = 1
"512" = 2
"1024" = 3

For weighting:

"a" = 0
"b" = 1
"c" = 2
"d" = 3
"z" = 4
"itu_r_468" = 5

request/sound_pressure_level_bricklet/<UID>/get_configuration¶

Request:	empty payload
Response:	fft_size – Type: int, Range: See symbols, Default: 3 weighting – Type: int, Range: See symbols, Default: 0

Returns the configuration as set by request/sound_pressure_level_bricklet/<UID>/set_configuration.

The following symbols are available for this function:

For fft_size:

"128" = 0
"256" = 1
"512" = 2
"1024" = 3

For weighting:

"a" = 0
"b" = 1
"c" = 2
"d" = 3
"z" = 4
"itu_r_468" = 5

Advanced Functions¶

request/sound_pressure_level_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/sound_pressure_level_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/sound_pressure_level_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/sound_pressure_level_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/sound_pressure_level_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/sound_pressure_level_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/sound_pressure_level_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 Sound Pressure Level's name in a human readable form.

Callback Configuration Functions¶

request/sound_pressure_level_bricklet/<UID>/set_decibel_callback_configuration¶

Request:	period – Type: int, Unit: 1 ms, Range: [0 to 2³² - 1], Default: 0 value_has_to_change – Type: bool, Default: false option – Type: char, Range: See symbols, Default: "x" min – Type: int, Unit: 1/10 dB, Range: [0 to 2¹⁶ - 1], Default: 0 max – Type: int, Unit: 1/10 dB, Range: [0 to 2¹⁶ - 1], Default: 0
Response:	no response

The period is the period with which the register/sound_pressure_level_bricklet/<UID>/decibel 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.

It is furthermore possible to constrain the callback with thresholds.

The option-parameter together with min/max sets a threshold for the register/sound_pressure_level_bricklet/<UID>/decibel callback.

The following options are possible:

Option	Description
'x'	Threshold is turned off
'o'	Threshold is triggered when the value is outside the min and max values
'i'	Threshold is triggered when the value is inside or equal to the min and max values
'<'	Threshold is triggered when the value is smaller than the min value (max is ignored)
'>'	Threshold is triggered when the value is greater than the min value (max is ignored)

If the option is set to 'x' (threshold turned off) the callback is triggered with the fixed period.

The following symbols are available for this function:

For option:

"off" = "x"
"outside" = "o"
"inside" = "i"
"smaller" = "<"
"greater" = ">"

request/sound_pressure_level_bricklet/<UID>/get_decibel_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 option – Type: char, Range: See symbols, Default: "x" min – Type: int, Unit: 1/10 dB, Range: [0 to 2¹⁶ - 1], Default: 0 max – Type: int, Unit: 1/10 dB, Range: [0 to 2¹⁶ - 1], Default: 0

Returns the callback configuration as set by request/sound_pressure_level_bricklet/<UID>/set_decibel_callback_configuration.

The following symbols are available for this function:

For option:

"off" = "x"
"outside" = "o"
"inside" = "i"
"smaller" = "<"
"greater" = ">"

request/sound_pressure_level_bricklet/<UID>/set_spectrum_callback_configuration¶

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

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

Every new measured spectrum will be send at most once. Set the period to 1 to make sure that you get every spectrum.

request/sound_pressure_level_bricklet/<UID>/get_spectrum_callback_configuration¶

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

Returns the callback configuration as set by request/sound_pressure_level_bricklet/<UID>/get_spectrum_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/sound_pressure_level_bricklet/<UID>/decibel¶

Register Request:	register – Type: bool
Callback Response:	decibel – Type: int, Unit: 1/10 dB, Range: [0 to 120]

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

This callback is triggered periodically according to the configuration set by request/sound_pressure_level_bricklet/<UID>/set_decibel_callback_configuration.

The callback payload is the same as request/sound_pressure_level_bricklet/<UID>/get_decibel.

register/sound_pressure_level_bricklet/<UID>/spectrum¶

Register Request:	register – Type: bool
Callback Response:	spectrum – Type: [int, ...], Length: variable, Unit: ? dB, Range: [0 to 2¹⁶ - 1]

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

This callback is triggered periodically according to the configuration set by request/sound_pressure_level_bricklet/<UID>/set_spectrum_callback_configuration.

The callback payload is the same as request/sound_pressure_level_bricklet/<UID>/get_spectrum.

Note

If reconstructing the value fails, the callback is triggered with null for spectrum.

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/sound_pressure_level_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/sound_pressure_level_bricklet/<UID>/get_bootloader_mode¶

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

Returns the current bootloader mode, see request/sound_pressure_level_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/sound_pressure_level_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/sound_pressure_level_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/sound_pressure_level_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/sound_pressure_level_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/sound_pressure_level_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/sound_pressure_level_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.