Barometer Bricklet

Features

  • Measures air pressure and altitude changes
  • Resolution 0.012mbar / 0.1m
  • Range 10 to 1200mbar

Description

The Barometer Bricklet can be used to extend the features of Bricks by the capability to measure air pressure in range of 10 to 1200mbar with a resolution of 0.012mbar. The measurement is temperature compensated internally. The Bricklet is equipped with a MS5611-01BA01 sensor which is designed to be used as an altimeter, too. But since the air pressure is changing significantly even over a short period time the achievable accuracy is limited. One possible solution to achieve higher accuracy and stability of the altitude measurement is to perform sensor fusion with the sensor data of an IMU Brick (see Youtube video).

Technical Specifications

Property Value
Sensor MS5611-01BA01
Current Consumption 1mA
   
Pressure Range 10 - 1200mbar
Resolution 0.012mbar / 0.1m
Accuracy (25°C, 750mbar) +- 1.5mbar
   
Dimensions (W x D x H) 25 x 15 x 5mm (0.98 x 0.59 x 0.19")
Weight 2g

Resources

Test your Barometer Bricklet

To test a Barometer Bricklet you need to have Brick Daemon and Brick Viewer installed. Brick Daemon acts as a proxy between the USB interface of the Bricks and the API bindings. Brick Viewer connects to Brick Daemon. It helps to figure out basic information about the connected Bricks and Bricklets and allows to test them.

Connect the Barometer Bricklet to a Brick with a Bricklet Cable.

If you connect the Brick to the PC over USB, you should see a new tab named "Barometer Bricklet" in the Brick Viewer after a moment. Select this tab. If everything went as expected you can now see the air pressure in mbar and a graph that shows the air pressure over time.

Barometer Bricklet in Brick Viewer

After this test you can go on with writing your own application. See the Programming Interface section for the API of the Barometer Bricklet and examples in different programming languages.

Understanding Air Pressure

Air pressure is a complex topic. Two frequently asked questions are: Why does the air pressure value of the Barometer Bricklet differs from the value in the weather forecast and why does the altitude value differ from the actual altitude of the measuring location?

Air Pressure Reading

The Barometer Bricklet outputs the air pressure in relation to the altitude of the measuring location, known as QFE value in aviation. The weather forecast reports air pressure in relation to mean sea level (the value is also temperature-corrected in a special way), known as QFF value in aviation.

With the barometric formula the QFF value can be approximated based on the the QFE value:

QFF = QFE / [1 - Tg * H / (273.15 + Tfe + Tg * H)] ^ (0.034163 / Tg)
  • Tg is the temperature lapse rate, that specifies how fast the temperature drops with increasing altitude (a common approximation under normal conditions is 0.0065 °C/Meter)
  • Tfe is the temperature at the measuring location in °C
  • H is the altitude of the measuring location in Meters

Here is an online calculator for this formula. The altitude of the measuring location can be found with Google Maps.

Altitude Reading

The altitude value for the Barometer Bricklets is by default calculated for a reference air pressure of 1013.25 mbar using an approximation of the International Standard Atmosphere model. An altitude value calculated like this is known as QNE value in aviation.

For a more exact altitude value in relation to mean sea level the reference air pressure for the measuring location has to be specified. In aviation the QNH value is used for this purpose. Therefore, this value if often available at airfields. Instead of the QNH value the QFF value can be used also. The QFF value has a different temperature-correction applied to it compared to the QNH, but the values are similar under normal conditions.

Case

A laser-cut case for the Barometer Bricklet is available.

Case for Barometer Bricklet

The assembly is easiest if you follow the following steps:

  • Screw spacers to the Bricklet,
  • screw bottom plate to bottom spacers,
  • build up side plates,
  • plug side plates into bottom plate and
  • screw top plate to top spacers.

Below you can see an exploded assembly drawing of the Barometer Bricklet case:

Exploded assembly drawing for Barometer Bricklet

Hint: There is a protective film on both sides of the plates, you have to remove it before assembly.

Programming Interface

See Programming Interface for a detailed description.

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