Modbus - Barometer Bricklet 2.0

This is the description of the Modbus protocol for the Barometer Bricklet 2.0. General information and technical specifications for the Barometer Bricklet 2.0 are summarized in its hardware description.

API

A general description of the Modbus protocol structure can be found here.

Basic Functions

BrickletBarometerV2.get_air_pressure
Function ID:

1

Request:

empty payload

Response:
  • air_pressure -- int32

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 CALLBACK_AIR_PRESSURE callback. You can set the callback configuration with set_air_pressure_callback_configuration.

BrickletBarometerV2.get_altitude
Function ID:

5

Request:

empty payload

Response:
  • altitude -- int32

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 set_reference_air_pressure.

If you want to get the value periodically, it is recommended to use the CALLBACK_ALTITUDE callback. You can set the callback configuration with set_altitude_callback_configuration.

BrickletBarometerV2.get_temperature
Function ID:

9

Request:

empty payload

Response:
  • temperature -- int32

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 CALLBACK_TEMPERATURE callback. You can set the callback configuration with set_temperature_callback_configuration.

BrickletBarometerV2.set_moving_average_configuration
Function ID:

13

Request:
  • moving_average_length_air_pressure -- uint16
  • moving_average_length_temperature -- uint16
Response:

no response

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.

BrickletBarometerV2.get_moving_average_configuration
Function ID:

14

Request:

empty payload

Response:
  • moving_average_length_air_pressure -- uint16
  • moving_average_length_temperature -- uint16

Returns the moving average configuration as set by set_moving_average_configuration.

BrickletBarometerV2.set_reference_air_pressure
Function ID:

15

Request:
  • air_pressure -- int32
Response:

no response

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.

BrickletBarometerV2.get_reference_air_pressure
Function ID:

16

Request:

empty payload

Response:
  • air_pressure -- int32

Returns the reference air pressure as set by set_reference_air_pressure.

Advanced Functions

BrickletBarometerV2.set_calibration
Function ID:

17

Request:
  • measured_air_pressure -- int32
  • actual_air_pressure -- int32
Response:

no response

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.

BrickletBarometerV2.get_calibration
Function ID:

18

Request:

empty payload

Response:
  • measured_air_pressure -- int32
  • actual_air_pressure -- int32

Returns the air pressure one point calibration values as set by set_calibration.

BrickletBarometerV2.set_sensor_configuration
Function ID:

19

Request:
  • data_rate -- uint8
  • air_pressure_low_pass_filter -- uint8
Response:

no response

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 meanings are defined for the parameters of this function:

  • 0: off, for data_rate
  • 1: 1hz, for data_rate
  • 2: 10hz, for data_rate
  • 3: 25hz, for data_rate
  • 4: 50hz, for data_rate
  • 5: 75hz, for data_rate
  • 0: off, for air_pressure_low_pass_filter
  • 1: 1 9th, for air_pressure_low_pass_filter
  • 2: 1 20th, for air_pressure_low_pass_filter
BrickletBarometerV2.get_sensor_configuration
Function ID:

20

Request:

empty payload

Response:
  • data_rate -- uint8
  • air_pressure_low_pass_filter -- uint8

Returns the sensor configuration as set by set_sensor_configuration.

The following meanings are defined for the parameters of this function:

  • 0: off, for data_rate
  • 1: 1hz, for data_rate
  • 2: 10hz, for data_rate
  • 3: 25hz, for data_rate
  • 4: 50hz, for data_rate
  • 5: 75hz, for data_rate
  • 0: off, for air_pressure_low_pass_filter
  • 1: 1 9th, for air_pressure_low_pass_filter
  • 2: 1 20th, for air_pressure_low_pass_filter
BrickletBarometerV2.get_spitfp_error_count
Function ID:

234

Request:

empty payload

Response:
  • error_count_ack_checksum -- uint32
  • error_count_message_checksum -- uint32
  • error_count_frame -- uint32
  • error_count_overflow -- uint32

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.

BrickletBarometerV2.set_bootloader_mode
Function ID:

235

Request:
  • mode -- uint8
Response:
  • status -- uint8

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 meanings are defined for the parameters of this function:

  • 0: bootloader, for mode
  • 1: firmware, for mode
  • 2: bootloader wait for reboot, for mode
  • 3: firmware wait for reboot, for mode
  • 4: firmware wait for erase and reboot, for mode
  • 0: ok, for status
  • 1: invalid mode, for status
  • 2: no change, for status
  • 3: entry function not present, for status
  • 4: device identifier incorrect, for status
  • 5: crc mismatch, for status
BrickletBarometerV2.get_bootloader_mode
Function ID:

236

Request:

empty payload

Response:
  • mode -- uint8

Returns the current bootloader mode, see set_bootloader_mode.

The following meanings are defined for the parameters of this function:

  • 0: bootloader, for mode
  • 1: firmware, for mode
  • 2: bootloader wait for reboot, for mode
  • 3: firmware wait for reboot, for mode
  • 4: firmware wait for erase and reboot, for mode
BrickletBarometerV2.set_write_firmware_pointer
Function ID:

237

Request:
  • pointer -- uint32
Response:

no response

Sets the firmware pointer for 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.

BrickletBarometerV2.write_firmware
Function ID:

238

Request:
  • data -- uint8[64]
Response:
  • status -- uint8

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

BrickletBarometerV2.set_status_led_config
Function ID:

239

Request:
  • config -- uint8
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 meanings are defined for the parameters of this function:

  • 0: off, for config
  • 1: on, for config
  • 2: show heartbeat, for config
  • 3: show status, for config
BrickletBarometerV2.get_status_led_config
Function ID:

240

Request:

empty payload

Response:
  • config -- uint8

Returns the configuration as set by set_status_led_config

The following meanings are defined for the parameters of this function:

  • 0: off, for config
  • 1: on, for config
  • 2: show heartbeat, for config
  • 3: show status, for config
BrickletBarometerV2.get_chip_temperature
Function ID:

242

Request:

empty payload

Response:
  • temperature -- int16

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.

BrickletBarometerV2.reset
Function ID:243
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!

BrickletBarometerV2.write_uid
Function ID:

248

Request:
  • uid -- uint32
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.

BrickletBarometerV2.read_uid
Function ID:

249

Request:

empty payload

Response:
  • uid -- uint32

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

BrickletBarometerV2.get_identity
Function ID:

255

Request:

empty payload

Response:
  • uid -- char[8]
  • connected_uid -- char[8]
  • position -- char
  • hardware_version -- uint8[3]
  • firmware_version -- uint8[3]
  • device_identifier -- uint16

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

Callback Configuration Functions

BrickletBarometerV2.set_air_pressure_callback_configuration
Function ID:

2

Request:
  • period -- uint32
  • value_has_to_change -- bool
  • option -- char
  • min -- int32
  • max -- int32
Response:

no response

The period in ms is the period with which the CALLBACK_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 CALLBACK_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 meanings are defined for the parameters of this function:

  • x: off, for option
  • o: outside, for option
  • i: inside, for option
  • <: smaller, for option
  • >: greater, for option
BrickletBarometerV2.get_air_pressure_callback_configuration
Function ID:

3

Request:

empty payload

Response:
  • period -- uint32
  • value_has_to_change -- bool
  • option -- char
  • min -- int32
  • max -- int32

Returns the callback configuration as set by set_air_pressure_callback_configuration.

The following meanings are defined for the parameters of this function:

  • x: off, for option
  • o: outside, for option
  • i: inside, for option
  • <: smaller, for option
  • >: greater, for option
BrickletBarometerV2.set_altitude_callback_configuration
Function ID:

6

Request:
  • period -- uint32
  • value_has_to_change -- bool
  • option -- char
  • min -- int32
  • max -- int32
Response:

no response

The period in ms is the period with which the CALLBACK_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 CALLBACK_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 meanings are defined for the parameters of this function:

  • x: off, for option
  • o: outside, for option
  • i: inside, for option
  • <: smaller, for option
  • >: greater, for option
BrickletBarometerV2.get_altitude_callback_configuration
Function ID:

7

Request:

empty payload

Response:
  • period -- uint32
  • value_has_to_change -- bool
  • option -- char
  • min -- int32
  • max -- int32

Returns the callback configuration as set by set_altitude_callback_configuration.

The following meanings are defined for the parameters of this function:

  • x: off, for option
  • o: outside, for option
  • i: inside, for option
  • <: smaller, for option
  • >: greater, for option
BrickletBarometerV2.set_temperature_callback_configuration
Function ID:

10

Request:
  • period -- uint32
  • value_has_to_change -- bool
  • option -- char
  • min -- int32
  • max -- int32
Response:

no response

The period in ms is the period with which the CALLBACK_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 CALLBACK_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 meanings are defined for the parameters of this function:

  • x: off, for option
  • o: outside, for option
  • i: inside, for option
  • <: smaller, for option
  • >: greater, for option
BrickletBarometerV2.get_temperature_callback_configuration
Function ID:

11

Request:

empty payload

Response:
  • period -- uint32
  • value_has_to_change -- bool
  • option -- char
  • min -- int32
  • max -- int32

Returns the callback configuration as set by set_temperature_callback_configuration.

The following meanings are defined for the parameters of this function:

  • x: off, for option
  • o: outside, for option
  • i: inside, for option
  • <: smaller, for option
  • >: greater, for option

Callbacks

BrickletBarometerV2.CALLBACK_AIR_PRESSURE
Function ID:

4

Response:
  • air_pressure -- int32

This callback is triggered periodically according to the configuration set by set_air_pressure_callback_configuration.

The response value is the same as get_air_pressure.

BrickletBarometerV2.CALLBACK_ALTITUDE
Function ID:

8

Response:
  • altitude -- int32

This callback is triggered periodically according to the configuration set by set_altitude_callback_configuration.

The response value is the same as get_altitude.

BrickletBarometerV2.CALLBACK_TEMPERATURE
Function ID:

12

Response:
  • temperature -- int32

This callback is triggered periodically according to the configuration set by set_temperature_callback_configuration.

The response value is the same as get_temperature.