MATLAB/Octave - Sound Pressure Level Bricklet

This is the description of the MATLAB/Octave 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 MATLAB/Octave API bindings is part of their general description.

Examples

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

Simple (MATLAB)

Download (matlab_example_simple.m)

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function matlab_example_simple()
    import com.tinkerforge.IPConnection;
    import com.tinkerforge.BrickletSoundPressureLevel;

    HOST = 'localhost';
    PORT = 4223;
    UID = 'XYZ'; % Change XYZ to the UID of your Sound Pressure Level Bricklet

    ipcon = IPConnection(); % Create IP connection
    spl = handle(BrickletSoundPressureLevel(UID, ipcon), 'CallbackProperties'); % Create device object

    ipcon.connect(HOST, PORT); % Connect to brickd
    % Don't use device before ipcon is connected

    % Get current decibel
    decibel = spl.getDecibel();
    fprintf('Decibel: %g dB(A)\n', decibel/10.0);

    input('Press key to exit\n', 's');
    ipcon.disconnect();
end

Callback (MATLAB)

Download (matlab_example_callback.m)

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function matlab_example_callback()
    import com.tinkerforge.IPConnection;
    import com.tinkerforge.BrickletSoundPressureLevel;

    HOST = 'localhost';
    PORT = 4223;
    UID = 'XYZ'; % Change XYZ to the UID of your Sound Pressure Level Bricklet

    ipcon = IPConnection(); % Create IP connection
    spl = handle(BrickletSoundPressureLevel(UID, ipcon), 'CallbackProperties'); % Create device object

    ipcon.connect(HOST, PORT); % Connect to brickd
    % Don't use device before ipcon is connected

    % Register decibel callback to function cb_decibel
    set(spl, 'DecibelCallback', @(h, e) cb_decibel(e));

    % Set period for decibel callback to 1s (1000ms) without a threshold
    spl.setDecibelCallbackConfiguration(1000, false, 'x', 0, 0);

    input('Press key to exit\n', 's');
    ipcon.disconnect();
end

% Callback function for decibel callback
function cb_decibel(e)
    fprintf('Decibel: %g dB(A)\n', e.decibel/10.0);
end

Threshold (MATLAB)

Download (matlab_example_threshold.m)

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function matlab_example_threshold()
    import com.tinkerforge.IPConnection;
    import com.tinkerforge.BrickletSoundPressureLevel;

    HOST = 'localhost';
    PORT = 4223;
    UID = 'XYZ'; % Change XYZ to the UID of your Sound Pressure Level Bricklet

    ipcon = IPConnection(); % Create IP connection
    spl = handle(BrickletSoundPressureLevel(UID, ipcon), 'CallbackProperties'); % Create device object

    ipcon.connect(HOST, PORT); % Connect to brickd
    % Don't use device before ipcon is connected

    % Register decibel callback to function cb_decibel
    set(spl, 'DecibelCallback', @(h, e) cb_decibel(e));

    % Configure threshold for decibel "greater than 60 dB(A)"
    % with a debounce period of 1s (1000ms)
    spl.setDecibelCallbackConfiguration(1000, false, '>', 60*10, 0);

    input('Press key to exit\n', 's');
    ipcon.disconnect();
end

% Callback function for decibel callback
function cb_decibel(e)
    fprintf('Decibel: %g dB(A)\n', e.decibel/10.0);
end

Simple (Octave)

Download (octave_example_simple.m)

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function octave_example_simple()
    more off;

    HOST = "localhost";
    PORT = 4223;
    UID = "XYZ"; % Change XYZ to the UID of your Sound Pressure Level Bricklet

    ipcon = javaObject("com.tinkerforge.IPConnection"); % Create IP connection
    spl = javaObject("com.tinkerforge.BrickletSoundPressureLevel", UID, ipcon); % Create device object

    ipcon.connect(HOST, PORT); % Connect to brickd
    % Don't use device before ipcon is connected

    % Get current decibel
    decibel = spl.getDecibel();
    fprintf("Decibel: %g dB(A)\n", decibel/10.0);

    input("Press key to exit\n", "s");
    ipcon.disconnect();
end

Callback (Octave)

Download (octave_example_callback.m)

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function octave_example_callback()
    more off;

    HOST = "localhost";
    PORT = 4223;
    UID = "XYZ"; % Change XYZ to the UID of your Sound Pressure Level Bricklet

    ipcon = javaObject("com.tinkerforge.IPConnection"); % Create IP connection
    spl = javaObject("com.tinkerforge.BrickletSoundPressureLevel", UID, ipcon); % Create device object

    ipcon.connect(HOST, PORT); % Connect to brickd
    % Don't use device before ipcon is connected

    % Register decibel callback to function cb_decibel
    spl.addDecibelCallback(@cb_decibel);

    % Set period for decibel callback to 1s (1000ms) without a threshold
    spl.setDecibelCallbackConfiguration(1000, false, "x", 0, 0);

    input("Press key to exit\n", "s");
    ipcon.disconnect();
end

% Callback function for decibel callback
function cb_decibel(e)
    fprintf("Decibel: %g dB(A)\n", e.decibel/10.0);
end

Threshold (Octave)

Download (octave_example_threshold.m)

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function octave_example_threshold()
    more off;

    HOST = "localhost";
    PORT = 4223;
    UID = "XYZ"; % Change XYZ to the UID of your Sound Pressure Level Bricklet

    ipcon = javaObject("com.tinkerforge.IPConnection"); % Create IP connection
    spl = javaObject("com.tinkerforge.BrickletSoundPressureLevel", UID, ipcon); % Create device object

    ipcon.connect(HOST, PORT); % Connect to brickd
    % Don't use device before ipcon is connected

    % Register decibel callback to function cb_decibel
    spl.addDecibelCallback(@cb_decibel);

    % Configure threshold for decibel "greater than 60 dB(A)"
    % with a debounce period of 1s (1000ms)
    spl.setDecibelCallbackConfiguration(1000, false, ">", 60*10, 0);

    input("Press key to exit\n", "s");
    ipcon.disconnect();
end

% Callback function for decibel callback
function cb_decibel(e)
    fprintf("Decibel: %g dB(A)\n", e.decibel/10.0);
end

API

Generally, every method of the MATLAB bindings that returns a value can throw a TimeoutException. This exception gets thrown if the device did not respond. If a cable based connection is used, it is unlikely that this exception gets thrown (assuming nobody unplugs the device). However, if a wireless connection is used, timeouts will occur if the distance to the device gets too big.

Beside the TimeoutException there is also a NotConnectedException that is thrown if a method needs to communicate with the device while the IP Connection is not connected.

Since the MATLAB bindings are based on Java and Java does not support multiple return values and return by reference is not possible for primitive types, we use small classes that only consist of member variables. The member variables of the returned objects are described in the corresponding method descriptions.

The package for all Brick/Bricklet bindings and the IP Connection is com.tinkerforge.*

All methods listed below are thread-safe.

Basic Functions

public class BrickletSoundPressureLevel(String uid, IPConnection ipcon)

Creates an object with the unique device ID uid.

In MATLAB:

import com.tinkerforge.BrickletSoundPressureLevel;

soundPressureLevel = BrickletSoundPressureLevel('YOUR_DEVICE_UID', ipcon);

In Octave:

soundPressureLevel = java_new("com.tinkerforge.BrickletSoundPressureLevel", "YOUR_DEVICE_UID", ipcon);

This object can then be used after the IP Connection is connected (see examples above).

public int getDecibel()

Returns the measured sound pressure in decibels. The values are given in dB/10 (tenths dB).

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 setConfiguration().

By default dB(A) will be used.

If you want to get the value periodically, it is recommended to use the DecibelCallback callback. You can set the callback configuration with setDecibelCallbackConfiguration().

public int[] getSpectrum()

Returns the frequency spectrum. The length of the spectrum is between 512 (FFT size 1024) and 64 (FFT size 128). See setConfiguration().

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 setConfiguration() 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.

public void setConfiguration(int fftSize, int weighting)

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 defaults are FFT size 1024 and weighting standard dB(A).

The following constants are available for this function:

  • BrickletSoundPressureLevel.FFT_SIZE_128 = 0
  • BrickletSoundPressureLevel.FFT_SIZE_256 = 1
  • BrickletSoundPressureLevel.FFT_SIZE_512 = 2
  • BrickletSoundPressureLevel.FFT_SIZE_1024 = 3
  • BrickletSoundPressureLevel.WEIGHTING_A = 0
  • BrickletSoundPressureLevel.WEIGHTING_B = 1
  • BrickletSoundPressureLevel.WEIGHTING_C = 2
  • BrickletSoundPressureLevel.WEIGHTING_D = 3
  • BrickletSoundPressureLevel.WEIGHTING_Z = 4
  • BrickletSoundPressureLevel.WEIGHTING_ITU_R_468 = 5
public BrickletSoundPressureLevel.Configuration getConfiguration()

Returns the configuration as set by setConfiguration().

The following constants are available for this function:

  • BrickletSoundPressureLevel.FFT_SIZE_128 = 0
  • BrickletSoundPressureLevel.FFT_SIZE_256 = 1
  • BrickletSoundPressureLevel.FFT_SIZE_512 = 2
  • BrickletSoundPressureLevel.FFT_SIZE_1024 = 3
  • BrickletSoundPressureLevel.WEIGHTING_A = 0
  • BrickletSoundPressureLevel.WEIGHTING_B = 1
  • BrickletSoundPressureLevel.WEIGHTING_C = 2
  • BrickletSoundPressureLevel.WEIGHTING_D = 3
  • BrickletSoundPressureLevel.WEIGHTING_Z = 4
  • BrickletSoundPressureLevel.WEIGHTING_ITU_R_468 = 5

The returned object has the public member variables int fftSize and int weighting.

Advanced Functions

public int[] getAPIVersion()

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.

public boolean getResponseExpected(int functionId)

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 setResponseExpected(). 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 setResponseExpected() for the list of function ID constants available for this function.

public void setResponseExpected(int functionId, boolean responseExpected)

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 constants are available for this function:

  • BrickletSoundPressureLevel.FUNCTION_SET_DECIBEL_CALLBACK_CONFIGURATION = 2
  • BrickletSoundPressureLevel.FUNCTION_SET_SPECTRUM_CALLBACK_CONFIGURATION = 6
  • BrickletSoundPressureLevel.FUNCTION_SET_CONFIGURATION = 9
  • BrickletSoundPressureLevel.FUNCTION_SET_WRITE_FIRMWARE_POINTER = 237
  • BrickletSoundPressureLevel.FUNCTION_SET_STATUS_LED_CONFIG = 239
  • BrickletSoundPressureLevel.FUNCTION_RESET = 243
  • BrickletSoundPressureLevel.FUNCTION_WRITE_UID = 248
public void setResponseExpectedAll(boolean responseExpected)

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

public BrickletSoundPressureLevel.SPITFPErrorCount getSPITFPErrorCount()

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.

The returned object has the public member variables long errorCountAckChecksum, long errorCountMessageChecksum, long errorCountFrame and long errorCountOverflow.

public int setBootloaderMode(int mode)

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 constants are available for this function:

  • BrickletSoundPressureLevel.BOOTLOADER_MODE_BOOTLOADER = 0
  • BrickletSoundPressureLevel.BOOTLOADER_MODE_FIRMWARE = 1
  • BrickletSoundPressureLevel.BOOTLOADER_MODE_BOOTLOADER_WAIT_FOR_REBOOT = 2
  • BrickletSoundPressureLevel.BOOTLOADER_MODE_FIRMWARE_WAIT_FOR_REBOOT = 3
  • BrickletSoundPressureLevel.BOOTLOADER_MODE_FIRMWARE_WAIT_FOR_ERASE_AND_REBOOT = 4
  • BrickletSoundPressureLevel.BOOTLOADER_STATUS_OK = 0
  • BrickletSoundPressureLevel.BOOTLOADER_STATUS_INVALID_MODE = 1
  • BrickletSoundPressureLevel.BOOTLOADER_STATUS_NO_CHANGE = 2
  • BrickletSoundPressureLevel.BOOTLOADER_STATUS_ENTRY_FUNCTION_NOT_PRESENT = 3
  • BrickletSoundPressureLevel.BOOTLOADER_STATUS_DEVICE_IDENTIFIER_INCORRECT = 4
  • BrickletSoundPressureLevel.BOOTLOADER_STATUS_CRC_MISMATCH = 5
public int getBootloaderMode()

Returns the current bootloader mode, see setBootloaderMode().

The following constants are available for this function:

  • BrickletSoundPressureLevel.BOOTLOADER_MODE_BOOTLOADER = 0
  • BrickletSoundPressureLevel.BOOTLOADER_MODE_FIRMWARE = 1
  • BrickletSoundPressureLevel.BOOTLOADER_MODE_BOOTLOADER_WAIT_FOR_REBOOT = 2
  • BrickletSoundPressureLevel.BOOTLOADER_MODE_FIRMWARE_WAIT_FOR_REBOOT = 3
  • BrickletSoundPressureLevel.BOOTLOADER_MODE_FIRMWARE_WAIT_FOR_ERASE_AND_REBOOT = 4
public void setWriteFirmwarePointer(long pointer)

Sets the firmware pointer for writeFirmware(). 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.

public int writeFirmware(int[] data)

Writes 64 Bytes of firmware at the position as written by setWriteFirmwarePointer() 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.

public void setStatusLEDConfig(int config)

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 constants are available for this function:

  • BrickletSoundPressureLevel.STATUS_LED_CONFIG_OFF = 0
  • BrickletSoundPressureLevel.STATUS_LED_CONFIG_ON = 1
  • BrickletSoundPressureLevel.STATUS_LED_CONFIG_SHOW_HEARTBEAT = 2
  • BrickletSoundPressureLevel.STATUS_LED_CONFIG_SHOW_STATUS = 3
public int getStatusLEDConfig()

Returns the configuration as set by setStatusLEDConfig()

The following constants are available for this function:

  • BrickletSoundPressureLevel.STATUS_LED_CONFIG_OFF = 0
  • BrickletSoundPressureLevel.STATUS_LED_CONFIG_ON = 1
  • BrickletSoundPressureLevel.STATUS_LED_CONFIG_SHOW_HEARTBEAT = 2
  • BrickletSoundPressureLevel.STATUS_LED_CONFIG_SHOW_STATUS = 3
public int getChipTemperature()

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.

public void 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!

public void writeUID(long uid)

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.

public long readUID()

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

public BrickletSoundPressureLevel.Identity getIdentity()

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.

The returned object has the public member variables String uid, String connectedUid, char position, int[] hardwareVersion, int[] firmwareVersion and int deviceIdentifier.

Callback Configuration Functions

public void setDecibelCallbackConfiguration(long period, boolean valueHasToChange, char option, int min, int max)

The period in ms is the period with which the DecibelCallback 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 DecibelCallback 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 default value is (0, false, 'x', 0, 0).

The following constants are available for this function:

  • BrickletSoundPressureLevel.THRESHOLD_OPTION_OFF = 'x'
  • BrickletSoundPressureLevel.THRESHOLD_OPTION_OUTSIDE = 'o'
  • BrickletSoundPressureLevel.THRESHOLD_OPTION_INSIDE = 'i'
  • BrickletSoundPressureLevel.THRESHOLD_OPTION_SMALLER = '<'
  • BrickletSoundPressureLevel.THRESHOLD_OPTION_GREATER = '>'
public BrickletSoundPressureLevel.DecibelCallbackConfiguration getDecibelCallbackConfiguration()

Returns the callback configuration as set by setDecibelCallbackConfiguration().

The following constants are available for this function:

  • BrickletSoundPressureLevel.THRESHOLD_OPTION_OFF = 'x'
  • BrickletSoundPressureLevel.THRESHOLD_OPTION_OUTSIDE = 'o'
  • BrickletSoundPressureLevel.THRESHOLD_OPTION_INSIDE = 'i'
  • BrickletSoundPressureLevel.THRESHOLD_OPTION_SMALLER = '<'
  • BrickletSoundPressureLevel.THRESHOLD_OPTION_GREATER = '>'

The returned object has the public member variables long period, boolean valueHasToChange, char option, int min and int max.

public void setSpectrumCallbackConfiguration(long period)

The period in ms is the period with which the SpectrumCallback 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.

The default value is 0.

public long getSpectrumCallbackConfiguration()

Returns the callback configuration as set by getSpectrumCallbackConfiguration().

Callbacks

Callbacks can be registered to receive time critical or recurring data from the device. The registration is done with "set" function of MATLAB. The parameters consist of the IP Connection object, the callback name and the callback function. For example, it looks like this in MATLAB:

function my_callback(e)
    fprintf('Parameter: %s\n', e.param);
end

set(device, 'ExampleCallback', @(h, e) my_callback(e));

Due to a difference in the Octave Java support the "set" function cannot be used in Octave. The registration is done with "add*Callback" functions of the device object. It looks like this in Octave:

function my_callback(e)
    fprintf("Parameter: %s\n", e.param);
end

device.addExampleCallback(@my_callback);

It is possible to add several callbacks and to remove them with the corresponding "remove*Callback" function.

The parameters of the callback are passed to the callback function as fields of the structure e, which is derived from the java.util.EventObject class. The available callback names with corresponding structure fields 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.

public callback BrickletSoundPressureLevel.DecibelCallback
Parameters:decibel -- int

This callback is triggered periodically according to the configuration set by setDecibelCallbackConfiguration().

The parameter is the same as getDecibel().

In MATLAB the set() function can be used to register a callback function to this callback.

In Octave a callback function can be added to this callback using the addDecibelCallback() function. An added callback function can be removed with the removeDecibelCallback() function.

public callback BrickletSoundPressureLevel.SpectrumCallback
Parameters:spectrum -- int[]

This callback is triggered periodically according to the configuration set by setSpectrumCallbackConfiguration().

The parameter is the same as getSpectrum().

In MATLAB the set() function can be used to register a callback function to this callback.

In Octave a callback function can be added to this callback using the addSpectrumCallback() function. An added callback function can be removed with the removeSpectrumCallback() function.

Constants

public static final int BrickletSoundPressureLevel.DEVICE_IDENTIFIER

This constant is used to identify a Sound Pressure Level Bricklet.

The getIdentity() function and the EnumerateCallback callback of the IP Connection have a deviceIdentifier parameter to specify the Brick's or Bricklet's type.

public static final String BrickletSoundPressureLevel.DEVICE_DISPLAY_NAME

This constant represents the human readable name of a Sound Pressure Level Bricklet.