MQTT - Barometer Bricklet 2.0

This is the description of the MQTT API bindings for the Barometer Bricklet 2.0. General information and technical specifications for the Barometer 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).

Callback

Download (example-callback.txt)

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# Change XYZ to the UID of your Barometer Bricklet 2.0

setup:
    # Handle incoming air pressure callbacks
    subscribe to tinkerforge/callback/barometer_v2_bricklet/XYZ/air_pressure
    publish '{"register": true}' to tinkerforge/register/barometer_v2_bricklet/XYZ/air_pressure # Register air_pressure callback
    
    # Set period for air pressure callback to 1s (1000ms) without a threshold
    publish '{"period": 1000, "value_has_to_change": false, "option": "off", "min": 0, "max": 0}' to tinkerforge/request/barometer_v2_bricklet/XYZ/set_air_pressure_callback_configuration

Simple

Download (example-simple.txt)

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# Change XYZ to the UID of your Barometer Bricklet 2.0

setup:
    # Get current air pressure
    subscribe to tinkerforge/response/barometer_v2_bricklet/XYZ/get_air_pressure
    publish '' to tinkerforge/request/barometer_v2_bricklet/XYZ/get_air_pressure
    
    # Get current altitude
    subscribe to tinkerforge/response/barometer_v2_bricklet/XYZ/get_altitude
    publish '' to tinkerforge/request/barometer_v2_bricklet/XYZ/get_altitude

Threshold

Download (example-threshold.txt)

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# Change XYZ to the UID of your Barometer Bricklet 2.0

setup:
    # Handle incoming air pressure callbacks
    subscribe to tinkerforge/callback/barometer_v2_bricklet/XYZ/air_pressure
    publish '{"register": true}' to tinkerforge/register/barometer_v2_bricklet/XYZ/air_pressure # Register air_pressure callback
    
    # Configure threshold for air pressure "greater than 1025 mbar"
    # with a debounce period of 1s (1000ms)
    publish '{"period": 1000, "value_has_to_change": false, "option": "greater", "min": 1025000, "max": 0}' to tinkerforge/request/barometer_v2_bricklet/XYZ/set_air_pressure_callback_configuration

API

All published payload to an from the MQTT bindings is in the 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/barometer_v2_bricklet/<UID>/get_air_pressure
Response payload:
 
  • air_pressure -- int

Returns the measured air pressure. The value has a range of 260000 to 1260000 and is given in mbar/1000, i.e. a value of 1001092 means that an air pressure of 1001.092 mbar is measured.

If you want to get the value periodically, it is recommended to use the register/barometer_v2_bricklet/<UID>/air_pressure callback. You can set the callback configuration with request/barometer_v2_bricklet/<UID>/set_air_pressure_callback_configuration.

request/barometer_v2_bricklet/<UID>/get_altitude
Response payload:
 
  • altitude -- int

Returns the relative altitude of the air pressure sensor. The value is given in mm and is calculated based on the difference between the current air pressure and the reference air pressure that can be set with request/barometer_v2_bricklet/<UID>/set_reference_air_pressure.

If you want to get the value periodically, it is recommended to use the register/barometer_v2_bricklet/<UID>/altitude callback. You can set the callback configuration with request/barometer_v2_bricklet/<UID>/set_altitude_callback_configuration.

request/barometer_v2_bricklet/<UID>/get_temperature
Response payload:
 
  • temperature -- int

Returns the temperature of the air pressure sensor. The value has a range of -4000 to 8500 and is given in °C/100, i.e. a value of 2007 means that a temperature of 20.07 °C is measured.

This temperature is used internally for temperature compensation of the air pressure measurement. It is not as accurate as the temperature measured by the Temperature Bricklet 2.0 or the Temperature IR Bricklet 2.0.

If you want to get the value periodically, it is recommended to use the register/barometer_v2_bricklet/<UID>/temperature callback. You can set the callback configuration with request/barometer_v2_bricklet/<UID>/set_temperature_callback_configuration.

request/barometer_v2_bricklet/<UID>/set_moving_average_configuration
Request payload:
 
  • moving_average_length_air_pressure -- int
  • moving_average_length_temperature -- int

Sets the length of a moving averaging for the air pressure and temperature measurements.

Setting the length to 1 will turn the averaging off. With less averaging, there is more noise on the data.

The range for the averaging is 1-1000.

If you want to do long term measurements the longest moving average will give the cleanest results.

The default value is 100.

request/barometer_v2_bricklet/<UID>/get_moving_average_configuration
Response payload:
 
  • moving_average_length_air_pressure -- int
  • moving_average_length_temperature -- int

Returns the moving average configuration as set by request/barometer_v2_bricklet/<UID>/set_moving_average_configuration.

request/barometer_v2_bricklet/<UID>/set_reference_air_pressure
Request payload:
 
  • air_pressure -- int

Sets the reference air pressure in mbar/1000 for the altitude calculation. Valid values are between 260000 and 1260000. Setting the reference to the current air pressure results in a calculated altitude of 0mm. Passing 0 is a shortcut for passing the current air pressure as reference.

Well known reference values are the Q codes QNH and QFE used in aviation.

The default value is 1013.25mbar.

request/barometer_v2_bricklet/<UID>/get_reference_air_pressure
Response payload:
 
  • air_pressure -- int

Returns the reference air pressure as set by request/barometer_v2_bricklet/<UID>/set_reference_air_pressure.

Advanced Functions

request/barometer_v2_bricklet/<UID>/set_calibration
Request payload:
 
  • measured_air_pressure -- int
  • actual_air_pressure -- int

Sets the one point calibration (OPC) values for the air pressure measurement.

Before the Bricklet can be calibrated any previous calibration has to be removed by setting measured air pressure and actual air pressure to 0.

Then the current air pressure has to be measured using the Bricklet (measured air pressure) and with and accurate reference barometer (actual air pressure) at the same time and passed to this function in mbar/1000.

After proper calibration the air pressure measurement can achieve an accuracy up to 0.2 mbar.

The calibration is saved in the EEPROM of the Bricklet and only needs to be configured once.

request/barometer_v2_bricklet/<UID>/get_calibration
Response payload:
 
  • measured_air_pressure -- int
  • actual_air_pressure -- int

Returns the air pressure one point calibration values as set by request/barometer_v2_bricklet/<UID>/set_calibration.

request/barometer_v2_bricklet/<UID>/set_sensor_configuration
Request payload:
 
  • data_rate -- int (has symbols)
  • air_pressure_low_pass_filter -- int (has symbols)

Configures the data rate and air pressure low pass filter. The low pass filter cut-off frequency (if enabled) can be set to 1/9th or 1/20th of the configure data rate to decrease the noise on the air pressure data.

The low pass filter configuration only applies to the air pressure measurement. There is no low pass filter for the temperature measurement.

A higher data rate will result in a less precise temperature because of self-heating of the sensor. If the accuracy of the temperature reading is important to you, we would recommend the 1Hz data rate.

The default values are 50Hz data rate and 1/9th low pass filter.

The following symbols are available for this function:

for data_rate:

  • "Off" = 0
  • "1Hz" = 1
  • "10Hz" = 2
  • "25Hz" = 3
  • "50Hz" = 4
  • "75Hz" = 5

for air_pressure_low_pass_filter:

  • "Off" = 0
  • "19th" = 1
  • "120th" = 2
request/barometer_v2_bricklet/<UID>/get_sensor_configuration
Response payload:
 
  • data_rate -- int (has symbols)
  • air_pressure_low_pass_filter -- int (has symbols)

Returns the sensor configuration as set by request/barometer_v2_bricklet/<UID>/set_sensor_configuration.

The following symbols are available for this function:

for data_rate:

  • "Off" = 0
  • "1Hz" = 1
  • "10Hz" = 2
  • "25Hz" = 3
  • "50Hz" = 4
  • "75Hz" = 5

for air_pressure_low_pass_filter:

  • "Off" = 0
  • "19th" = 1
  • "120th" = 2
request/barometer_v2_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/barometer_v2_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/barometer_v2_bricklet/<UID>/get_bootloader_mode
Response payload:
 
  • mode -- int (has symbols)

Returns the current bootloader mode, see request/barometer_v2_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/barometer_v2_bricklet/<UID>/set_write_firmware_pointer
Request payload:
 
  • pointer -- int

Sets the firmware pointer for request/barometer_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/barometer_v2_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/barometer_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/barometer_v2_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/barometer_v2_bricklet/<UID>/get_status_led_config
Response payload:
 
  • config -- int (has symbols)

Returns the configuration as set by request/barometer_v2_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/barometer_v2_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/barometer_v2_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/barometer_v2_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/barometer_v2_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/barometer_v2_bricklet/<UID>/get_identity
Response payload:
 
  • uid -- string
  • connected_uid -- string
  • position -- string
  • 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 Barometer 2.0's name in a human readable form.

Callback Configuration Functions

request/barometer_v2_bricklet/<UID>/set_air_pressure_callback_configuration
Request payload:
 
  • period -- int
  • value_has_to_change -- bool
  • option -- string (has symbols)
  • min -- int
  • max -- int

The period in ms is the period with which the register/barometer_v2_bricklet/<UID>/air_pressure 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/barometer_v2_bricklet/<UID>/air_pressure 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 symbols are available for this function:

for option:

  • "Off" = 'x'
  • "Outside" = 'o'
  • "Inside" = 'i'
  • "Smaller" = '<'
  • "Greater" = '>'
request/barometer_v2_bricklet/<UID>/get_air_pressure_callback_configuration
Response payload:
 
  • period -- int
  • value_has_to_change -- bool
  • option -- string (has symbols)
  • min -- int
  • max -- int

Returns the callback configuration as set by request/barometer_v2_bricklet/<UID>/set_air_pressure_callback_configuration.

The following symbols are available for this function:

for option:

  • "Off" = 'x'
  • "Outside" = 'o'
  • "Inside" = 'i'
  • "Smaller" = '<'
  • "Greater" = '>'
request/barometer_v2_bricklet/<UID>/set_altitude_callback_configuration
Request payload:
 
  • period -- int
  • value_has_to_change -- bool
  • option -- string (has symbols)
  • min -- int
  • max -- int

The period in ms is the period with which the register/barometer_v2_bricklet/<UID>/altitude 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/barometer_v2_bricklet/<UID>/altitude 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 symbols are available for this function:

for option:

  • "Off" = 'x'
  • "Outside" = 'o'
  • "Inside" = 'i'
  • "Smaller" = '<'
  • "Greater" = '>'
request/barometer_v2_bricklet/<UID>/get_altitude_callback_configuration
Response payload:
 
  • period -- int
  • value_has_to_change -- bool
  • option -- string (has symbols)
  • min -- int
  • max -- int

Returns the callback configuration as set by request/barometer_v2_bricklet/<UID>/set_altitude_callback_configuration.

The following symbols are available for this function:

for option:

  • "Off" = 'x'
  • "Outside" = 'o'
  • "Inside" = 'i'
  • "Smaller" = '<'
  • "Greater" = '>'
request/barometer_v2_bricklet/<UID>/set_temperature_callback_configuration
Request payload:
 
  • period -- int
  • value_has_to_change -- bool
  • option -- string (has symbols)
  • min -- int
  • max -- int

The period in ms is the period with which the register/barometer_v2_bricklet/<UID>/temperature 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/barometer_v2_bricklet/<UID>/temperature 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 symbols are available for this function:

for option:

  • "Off" = 'x'
  • "Outside" = 'o'
  • "Inside" = 'i'
  • "Smaller" = '<'
  • "Greater" = '>'
request/barometer_v2_bricklet/<UID>/get_temperature_callback_configuration
Response payload:
 
  • period -- int
  • value_has_to_change -- bool
  • option -- string (has symbols)
  • min -- int
  • max -- int

Returns the callback configuration as set by request/barometer_v2_bricklet/<UID>/set_temperature_callback_configuration.

The following symbols are available for this function:

for option:

  • "Off" = 'x'
  • "Outside" = 'o'
  • "Inside" = 'i'
  • "Smaller" = '<'
  • "Greater" = '>'

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/barometer_v2_bricklet/<UID>/air_pressure
Request payload:
 
  • register -- bool
Response payload:
 
  • air_pressure -- int

A callback can be registered for this event by publishing to the .../register/barometer_v2_bricklet/<UID>/air_pressure[/<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/barometer_v2_bricklet/<UID>/air_pressure[/<SUFFIX>] topic for each registered suffix.

This callback is triggered periodically according to the configuration set by request/barometer_v2_bricklet/<UID>/set_air_pressure_callback_configuration.

The callback payload is the same as request/barometer_v2_bricklet/<UID>/get_air_pressure.

register/barometer_v2_bricklet/<UID>/altitude
Request payload:
 
  • register -- bool
Response payload:
 
  • altitude -- int

A callback can be registered for this event by publishing to the .../register/barometer_v2_bricklet/<UID>/altitude[/<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/barometer_v2_bricklet/<UID>/altitude[/<SUFFIX>] topic for each registered suffix.

This callback is triggered periodically according to the configuration set by request/barometer_v2_bricklet/<UID>/set_altitude_callback_configuration.

The callback payload is the same as request/barometer_v2_bricklet/<UID>/get_altitude.

register/barometer_v2_bricklet/<UID>/temperature
Request payload:
 
  • register -- bool
Response payload:
 
  • temperature -- int

A callback can be registered for this event by publishing to the .../register/barometer_v2_bricklet/<UID>/temperature[/<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/barometer_v2_bricklet/<UID>/temperature[/<SUFFIX>] topic for each registered suffix.

This callback is triggered periodically according to the configuration set by request/barometer_v2_bricklet/<UID>/set_temperature_callback_configuration.

The callback payload is the same as request/barometer_v2_bricklet/<UID>/get_temperature.