STM MEMs pressure sensor, gyroscope and accelerometer hook up to ARM MBED

I used a header board for an STM MEMS evaluation kit in order to take a look at some common MEMS sensors:

  • LPS301: Pressure and temperature sensor
  • LG3D20: Gyroscope
  • LSM303DLHC: Accelerometer and magnetometer

The header was an STEVAL-MKI124V1 which is designed to work with an STM motherboard evaluation system. I took a shortcut and used it with an ARM MBED board featuring an NXP LPC1768 MBED.

Hook-up using I2C was trivial:

Screen Shot 2014-08-10 at 9.37.23 PM

The schematic for the evaluation board is here:

http://www.st.com/web/en/catalog/tools/PF253482

The orientation of the sensors on the board is like this:

Screen Shot 2014-08-10 at 9.38.10 PM

MBED-based code I write to drive the I2C is on the MBED website here

The code sets up each of the sensors and then provides a continuous output of temperature, pressure and orientation. Rather than optimize for performance or efficiency, the code here is intended to show clearly how to access the sensors.

An interesting twist was to use the linear accelerometer to find the vector of the earth’s gravitational field (i.e. down) and to use that to make a tilt-adjusted compass. Algorithm

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