The Barometer Bricklet 2.0 can be used to extend the features of Bricks by the capability to measure air pressure in range of 260 to 1260hPa with a resolution of 0.0075hPa. The measurement is temperature compensated internally.
The Bricklet is equipped with a LPS22HB sensor which can be used as an altimeter. Since the air pressure is changing significantly even over a short period of 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 2.0 (see Youtube video).
|Current Consumption||30mW (6mA at 5V)|
|Pressure Range||260 to 1260hPa|
|Resolution||0.0075hPa / 6.25cm|
|Accuracy (0-65°C)||±1.1hPa uncalibrated, ±0.2hPa calibrated|
|Temperature Range||-40 to +85°C|
|Dimensions (W x D x H)||25 x 15 x 5mm (0.98 x 0.59 x 0.19")|
To test a Barometer Bricklet 2.0 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 2.0 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 2.0" in the Brick Viewer after a moment. Select this tab. If everything went as expected you can now see the air pressure in hPa and a graph that shows the air pressure over time.
After this test you can go on with writing your own application. See the Programming Interface section for the API of the Barometer Bricklet 2.0 and examples in different programming languages.
Air pressure is a complex topic. Two frequently asked questions are: Why does the air pressure value of the Barometer Bricklet 2.0 differs from the value in the weather forecast and why does the altitude value differ from the actual altitude of the measuring location?
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)
Tgis the temperature lapse rate, that specifies how fast the temperature drops with increasing altitude (a common approximation under normal conditions is 0.0065°C/m)
Tfeis the temperature at the measuring location in °C
His 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.
The altitude value for the Barometer Bricklets is by default calculated for a reference air pressure of 1013.25hPa 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.
A laser-cut case for the Barometer Bricklet 2.0 is available.
The assembly is easiest if you follow the following steps:
Below you can see an exploded assembly drawing of the Barometer Bricklet 2.0 case:
Hint: There is a protective film on both sides of the plates, you have to remove it before assembly.
See Programming Interface for a detailed description.
|C/C++ for Microcontrollers||API||Examples||Installation|
|Visual Basic .NET||API||Examples||Installation|