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====== Barometer and altimeter ALTIMET01A ======

A digital barometric pressure sensor for precise measurements of altitude and temperature.
Sensor output is digital - either to SPI or I2C. It differs according to the type of fitted sensor.

{{:cs:modules:altimet01a_big.jpg?300|}}

[[http://www.mlab.cz/Modules/Sensors/ALTIMET01A/DOC/ALTIMET01A.cs.pdf|Original MLAB documentation]]

===== Module construction =====

The module is designed to be screwed to the base. The screws can be broken off, so the PCB can be glued directly to a flat surface, decreasing the weight and space requirements. You can see an example of this solution in [[en:uav]] construction.

==== Possible sensors ====

The module can be fitted with following sensor types:

  * [[http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=MPL115A|MPL115A1]] - SPI interface, power supply up to 5V.
  * MPL115A2 - I2C interface
  * [[http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=MPL3115A2|MPL3115A2]] - I2C interface with vertical pressure resolution 30cm and maximal power supply 3.6 V. This IO does not have SHDN signal and therefore there has to be a jumper fitted to module. 

==== Communication with sensors ====

MLAB documentation contains examples of connections for microcontrolers [[en:arm]], [[en:pic16f87xtq44|PIC]] and [[en:atmegatq32|AVR]].

Furthermore, both types of sensors (with I²C or SPI interface) can be read directly from the computer using a Python library [[en:pymlab|pymlab]] and conversion modules [[en:usbi2c|USBI2C]] and [[en:i2cspi|I2CSPI]].

{{ :cs:modules:altimet_i2c_spi_link.jpg?direct&300 | An example of connecting the SPI module version to PC. }}

===== Parameters =====

When measuring the parameters of MPL3115A2 during the [[en:abl|ABL01A]] project, we found out that the pressure measurements were functional at least up to 16 km (approximately 10kPa), a much better result than the parameter stated in the catalogue list. On the other hand, the internal pressure atmospheric model is only usable up to 10 km of altitude - in higher altitudes it experiences considerable inaccuracies. 


==== Module testing ====

The realisation of a testing system for MPL3115A2 sensor uses [[en:i2chub|I2CHUB02A]] module, that enables a testing of more sensors at once. Sensors are placed together in a vacuum bell with controlled pressure and the pressure measurements are (together with temperature measurements) read by [[en:i2c|I²C]] bus. At the same time, a pressure measured by a reference measuring device DPI 145 is read by the main computer.

{{:cs:modules:altimet01a_testing.jpg?300|}}{{:cs:modules:altimet01a_test_board.jpg?direct&400 |}}


Reading the pressure via I2C bus, a following python code was used: [[https://github.com/MLAB-project/MLAB-I2c-modules|External link]] 

==== Modul power supply ====

<WRAP warning round>
I2C module version has to be supplied by a stabilised voltage smaller than 3.6 V, otherwise it can be destroyed.

</WRAP>

===== Related sites =====

  * [[http://prezi.com/q40vh-gggjg7/poloautomaticky-merici-system-pro-kalibraci-vyskomeru/|A presentation of calibration system ]]