MQTT - Barometer Bricklet

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

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# Change XYZ to the UID of your Barometer Bricklet

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

Callback

Download (example-callback.txt)

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# Change XYZ to the UID of your Barometer Bricklet

setup:
    # Handle incoming air pressure callbacks
    subscribe to tinkerforge/callback/barometer_bricklet/XYZ/air_pressure
    publish '{"register": true}' to tinkerforge/register/barometer_bricklet/XYZ/air_pressure # Register air_pressure callback
    
    # Set period for air pressure callback to 1s (1000ms)
    # Note: The air pressure callback is only called every second
    #       if the air pressure has changed since the last call!
    publish '{"period": 1000}' to tinkerforge/request/barometer_bricklet/XYZ/set_air_pressure_callback_period

Threshold

Download (example-threshold.txt)

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# Change XYZ to the UID of your Barometer Bricklet

setup:
    # Get threshold callbacks with a debounce time of 10 seconds (10000ms)
    publish '{"debounce": 10000}' to tinkerforge/request/barometer_bricklet/XYZ/set_debounce_period
    
    # Handle incoming air pressure reached callbacks
    subscribe to tinkerforge/callback/barometer_bricklet/XYZ/air_pressure_reached
    publish '{"register": true}' to tinkerforge/register/barometer_bricklet/XYZ/air_pressure_reached # Register air_pressure_reached callback
    
    # Configure threshold for air pressure "greater than 1025 mbar"
    publish '{"option": "greater", "min": 1025000, "max": 0}' to tinkerforge/request/barometer_bricklet/XYZ/set_air_pressure_callback_threshold

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/barometer_bricklet/<UID>/get_air_pressure
Response payload:
 
  • air_pressure -- int

Returns the air pressure of the air pressure sensor. The value has a range of 10000 to 1200000 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 air pressure periodically, it is recommended to use the register/barometer_bricklet/<UID>/air_pressure callback and set the period with request/barometer_bricklet/<UID>/set_air_pressure_callback_period.

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

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

If you want to get the altitude periodically, it is recommended to use the register/barometer_bricklet/<UID>/altitude callback and set the period with request/barometer_bricklet/<UID>/set_altitude_callback_period.

request/barometer_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 10000 and 1200000. Setting the reference to the current air pressure results in a calculated altitude of 0cm. 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_bricklet/<UID>/get_reference_air_pressure
Response payload:
 
  • air_pressure -- int

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

Advanced Functions

request/barometer_bricklet/<UID>/get_chip_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 or the Temperature IR Bricklet.

request/barometer_bricklet/<UID>/set_averaging
Request payload:
 
  • moving_average_pressure -- int
  • average_pressure -- int
  • average_temperature -- int

Sets the different averaging parameters. It is possible to set the length of a normal averaging for the temperature and pressure, as well as an additional length of a moving average for the pressure. The moving average is calculated from the normal averages. There is no moving average for the temperature.

The maximum length for the pressure average is 10, for the temperature average is 255 and for the moving average is 25.

Setting the all three parameters to 0 will turn the averaging completely off. If the averaging is off, there is lots of noise on the data, but the data is without delay. Thus we recommend to turn the averaging off if the Barometer Bricklet data is to be used for sensor fusion with other sensors.

The default values are 10 for the normal averages and 25 for the moving average.

New in version 2.0.1 (Plugin).

request/barometer_bricklet/<UID>/get_averaging
Response payload:
 
  • moving_average_pressure -- int
  • average_pressure -- int
  • average_temperature -- int

Returns the averaging configuration as set by request/barometer_bricklet/<UID>/set_averaging.

New in version 2.0.1 (Plugin).

request/barometer_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's name in a human readable form.

Callback Configuration Functions

request/barometer_bricklet/<UID>/set_air_pressure_callback_period
Request payload:
 
  • period -- int

Sets the period in ms with which the register/barometer_bricklet/<UID>/air_pressure callback is triggered periodically. A value of 0 turns the callback off.

The register/barometer_bricklet/<UID>/air_pressure callback is only triggered if the air pressure has changed since the last triggering.

The default value is 0.

request/barometer_bricklet/<UID>/get_air_pressure_callback_period
Response payload:
 
  • period -- int

Returns the period as set by request/barometer_bricklet/<UID>/set_air_pressure_callback_period.

request/barometer_bricklet/<UID>/set_altitude_callback_period
Request payload:
 
  • period -- int

Sets the period in ms with which the register/barometer_bricklet/<UID>/altitude callback is triggered periodically. A value of 0 turns the callback off.

The register/barometer_bricklet/<UID>/altitude callback is only triggered if the altitude has changed since the last triggering.

The default value is 0.

request/barometer_bricklet/<UID>/get_altitude_callback_period
Response payload:
 
  • period -- int

Returns the period as set by request/barometer_bricklet/<UID>/set_altitude_callback_period.

request/barometer_bricklet/<UID>/set_air_pressure_callback_threshold
Request payload:
 
  • option -- string (has symbols)
  • min -- int
  • max -- int

Sets the thresholds for the register/barometer_bricklet/<UID>/air_pressure_reached callback.

The following options are possible:

Option Description
'x' Callback is turned off
'o' Callback is triggered when the air pressure is outside the min and max values
'i' Callback is triggered when the air pressure is inside the min and max values
'<' Callback is triggered when the air pressure is smaller than the min value (max is ignored)
'>' Callback is triggered when the air pressure is greater than the min value (max is ignored)

The default value is ('x', 0, 0).

The following symbols are available for this function:

for option:

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

Returns the threshold as set by request/barometer_bricklet/<UID>/set_air_pressure_callback_threshold.

The following symbols are available for this function:

for option:

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

Sets the thresholds for the register/barometer_bricklet/<UID>/altitude_reached callback.

The following options are possible:

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

The default value is ('x', 0, 0).

The following symbols are available for this function:

for option:

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

Returns the threshold as set by request/barometer_bricklet/<UID>/set_altitude_callback_threshold.

The following symbols are available for this function:

for option:

  • "Off" = 'x'
  • "Outside" = 'o'
  • "Inside" = 'i'
  • "Smaller" = '<'
  • "Greater" = '>'
request/barometer_bricklet/<UID>/set_debounce_period
Request payload:
 
  • debounce -- int

Sets the period in ms with which the threshold callbacks

are triggered, if the thresholds

keep being reached.

The default value is 100.

request/barometer_bricklet/<UID>/get_debounce_period
Response payload:
 
  • debounce -- int

Returns the debounce period as set by request/barometer_bricklet/<UID>/set_debounce_period.

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_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_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_bricklet/<UID>/air_pressure[/<SUFFIX>] topic for each registered suffix.

This callback is triggered periodically with the period that is set by request/barometer_bricklet/<UID>/set_air_pressure_callback_period. The callback payload is the air pressure of the air pressure sensor.

The register/barometer_bricklet/<UID>/air_pressure callback is only triggered if the air pressure has changed since the last triggering.

register/barometer_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_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_bricklet/<UID>/altitude[/<SUFFIX>] topic for each registered suffix.

This callback is triggered periodically with the period that is set by request/barometer_bricklet/<UID>/set_altitude_callback_period. The callback payload is the altitude of the air pressure sensor.

The register/barometer_bricklet/<UID>/altitude callback is only triggered if the altitude has changed since the last triggering.

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

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

This callback is triggered when the threshold as set by request/barometer_bricklet/<UID>/set_air_pressure_callback_threshold is reached. The callback payload is the air pressure of the air pressure sensor.

If the threshold keeps being reached, the callback is triggered periodically with the period as set by request/barometer_bricklet/<UID>/set_debounce_period.

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

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

This callback is triggered when the threshold as set by request/barometer_bricklet/<UID>/set_altitude_callback_threshold is reached. The callback payload is the altitude of the air pressure sensor.

If the threshold keeps being reached, the callback is triggered periodically with the period as set by request/barometer_bricklet/<UID>/set_debounce_period.