Software / API Bindings / MQTT / API Reference and Examples / Bricklets / Barometer Bricklet

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)

# 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)

# 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)

# 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 hPa"
    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 member _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¶

Request:	empty payload
Response:	air_pressure – Type: int, Unit: 1/1000 hPa, Range: [10000 to 1200000]

Returns the air pressure of the air pressure sensor.

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¶

Request:	empty payload
Response:	altitude – Type: int, Unit: 1 cm, Range: [-2³¹ to 2³¹ - 1]

Returns the relative altitude of the air pressure sensor. The value 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:	air_pressure – Type: int, Unit: 1/1000 hPa, Range: [0, 10000 to 1200000], Default: 1013250
Response:	no response

Sets the reference air pressure for the altitude calculation. 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.

request/barometer_bricklet/<UID>/get_reference_air_pressure¶

Request:	empty payload
Response:	air_pressure – Type: int, Unit: 1/1000 hPa, Range: [10000 to 1200000], Default: 1013250

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¶

Request:	empty payload
Response:	temperature – Type: int, Unit: 1/100 °C, Range: [-4000 to 8500]

Returns the temperature of the air pressure sensor.

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:	moving_average_pressure – Type: int, Range: [0 to 25], Default: 25 average_pressure – Type: int, Range: [0 to 10], Default: 10 average_temperature – Type: int, Range: [0 to 255], Default: 10
Response:	no response

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.

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.

New in version 2.0.1 (Plugin).

request/barometer_bricklet/<UID>/get_averaging¶

Request:	empty payload
Response:	moving_average_pressure – Type: int, Range: [0 to 25], Default: 25 average_pressure – Type: int, Range: [0 to 10], Default: 10 average_temperature – Type: int, Range: [0 to 255], Default: 10

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

New in version 2.0.1 (Plugin).

request/barometer_bricklet/<UID>/set_i2c_mode¶

Request:	mode – Type: int, Range: See symbols, Default: 0
Response:	no response

Sets the I2C mode. Possible modes are:

0: Fast (400kHz)
1: Slow (100kHz)

If you have problems with obvious outliers in the Barometer Bricklet measurements, they may be caused by EMI issues. In this case it may be helpful to lower the I2C speed.

It is however not recommended to lower the I2C speed in applications where a high throughput needs to be achieved.

The following symbols are available for this function:

For mode:

"fast" = 0
"slow" = 1

New in version 2.0.3 (Plugin).

request/barometer_bricklet/<UID>/get_i2c_mode¶

Request:	empty payload
Response:	mode – Type: int, Range: See symbols, Default: 0

Returns the I2C mode as set by request/barometer_bricklet/<UID>/set_i2c_mode.

The following symbols are available for this function:

For mode:

"fast" = 0
"slow" = 1

New in version 2.0.3 (Plugin).

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

Callback Configuration Functions¶

request/barometer_bricklet/<UID>/set_air_pressure_callback_period¶

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

Sets the period 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.

request/barometer_bricklet/<UID>/get_air_pressure_callback_period¶

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

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

request/barometer_bricklet/<UID>/set_altitude_callback_period¶

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

Sets the period 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.

request/barometer_bricklet/<UID>/get_altitude_callback_period¶

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

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

request/barometer_bricklet/<UID>/set_air_pressure_callback_threshold¶

Request:	option – Type: char, Range: See symbols, Default: "x" min – Type: int, Unit: 1/1000 hPa, Range: [-2³¹ to 2³¹ - 1], Default: 0 max – Type: int, Unit: 1/1000 hPa, Range: [-2³¹ to 2³¹ - 1], Default: 0
Response:	no response

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 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¶

Request:	empty payload
Response:	option – Type: char, Range: See symbols, Default: "x" min – Type: int, Unit: 1/1000 hPa, Range: [-2³¹ to 2³¹ - 1], Default: 0 max – Type: int, Unit: 1/1000 hPa, Range: [-2³¹ to 2³¹ - 1], Default: 0

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:	option – Type: char, Range: See symbols, Default: "x" min – Type: int, Unit: 1 cm, Range: [-2³¹ to 2³¹ - 1], Default: 0 max – Type: int, Unit: 1 cm, Range: [-2³¹ to 2³¹ - 1], Default: 0
Response:	no response

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 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¶

Request:	empty payload
Response:	option – Type: char, Range: See symbols, Default: "x" min – Type: int, Unit: 1 cm, Range: [-2³¹ to 2³¹ - 1], Default: 0 max – Type: int, Unit: 1 cm, Range: [-2³¹ to 2³¹ - 1], Default: 0

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:	debounce – Type: int, Unit: 1 ms, Range: [0 to 2³² - 1], Default: 100
Response:	no response

Sets the period with which the threshold callbacks

register/barometer_bricklet/<UID>/air_pressure_reached,
register/barometer_bricklet/<UID>/altitude_reached

are triggered, if the thresholds

request/barometer_bricklet/<UID>/set_air_pressure_callback_threshold,
request/barometer_bricklet/<UID>/set_altitude_callback_threshold

keep being reached.

request/barometer_bricklet/<UID>/get_debounce_period¶

Request:	empty payload
Response:	debounce – Type: int, Unit: 1 ms, Range: [0 to 2³² - 1], Default: 100

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¶

Register Request:	register – Type: bool
Callback Response:	air_pressure – Type: int, Unit: 1/1000 hPa, Range: [10000 to 1200000]

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¶

Register Request:	register – Type: bool
Callback Response:	altitude – Type: int, Unit: 1 cm, Range: [-2³¹ to 2³¹ - 1]

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¶

Register Request:	register – Type: bool
Callback Response:	air_pressure – Type: int, Unit: 1/1000 hPa, Range: [10000 to 1200000]

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¶

Register Request:	register – Type: bool
Callback Response:	altitude – Type: int, Unit: 1 cm, Range: [-2³¹ to 2³¹ - 1]

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.