What is it?

This is the MPU9250 9-axis motion sensor by Invensense with the MPL3115A2 pressure sensor/altimeter by Freescale mounted on a small pc board that is to be soldered to the bottom (pins 8 - 17) of the Teensy 3.1 microcontroller

Why did you make it?

The MPU9250 is one of only a few 9-axis combination accelerometer/gyroscope/magnetometer MEMS sensors available today. It's in a small 3 mm x 3 mm package and has a lot of functions but only one interrupt pin. I wanted to make use of the sensor for 9 DoF sensor fusion for motion sensing and motion control applications but do so with a very small footprint. The Teensy 3.1 microcontroller is a powerful Cortex M4 ARM-based microcontroller that is ideally suited for sensor fusion filtering. By designing a small pc board with the MPU9250 sensor that fit on a small portion of the Teensy 3.1, I can achieve absolute orientation sensing in a device package with an extremely small footprint with plenty of room (unoccupied pins) for expansion. Since the board is bigger than the similar micro add-on, I had room for an altimeter which provides a tenth degree of freedom well-suited to relative motion sensing for changes in height.

What makes it special?

This is the another example of the modular Teensy concept, where small special-purpose pc boards designed to be added on to the Teensy 3.1, either alone or in combination, can be mixed and matched for specific applications. In the works are pc boards for the other 9-axis motion sensor I know of, Bosch's BMX-055, in addition to the LSM9DS0 boards recently introduced. Each of these is coupled with an altimeter, and planned are boards for LiPo battery charging, Bluetooth Smart, and dc motor control. Others are likely to follow. The idea is to add modular capability while maintaining an extremely small, portable, low-power package. More on the concept can be found here.

I have designed a second version of this MPU9250 Mini Add-On MPU9250I2CTeensyShield.v03 board with the MS5637 altimeter instead of the MPL3115A2 pressure sensor/altimeter. The advantage is the small size (3 mm x 3 mm) of the former allowing the same 10 DoF sensors on both the mini-sized and micro-sized add-on boards. I am in the process of designing yet a third variant which will utilize ST Microelectronics' 2.5 mm x 2.5 mm LPS25HTR low-power, high-resolution pressure sensor. Sensors keep getting smaller and less power hungry, if not cheaper, and I am trying to keep up! Small, low-power for portable applications is where my interests lay.

I have written a program to get the properly-scaled sensor data from the accelerometer, gyro, magnetometer, altimeter, and thermometer sensors on the board, including gyro and accelerometer self-test, calibration, and Serial and lcd display functions. I have also added 9 DoF sensor fusion using open-source Madgwick and Mahony sensor fusion filter algorithms and i2c communication with the Teensy-3.1-specific i2c_t3.h Wire library. A general discusion of 9 DoF sensor fusion and motion control can be found here. The library to run sensor fusion on this MPU9250 Mini add-on with the Teensy 3.1 is reposited here.

Teensy 3.1 can be purchased from OSHPark for $17 and is not included with your purchase of this add on.

Order a board MPU9250I2CTeensyShield.v02 from OSHPark.com and make your own, or order from me and I'll do the work for you!