What is it?

The MPU9250 is a 9-axis motion sensor by Invensense with 16-bit resolution for the accelerometer, gyroscope, and magnetometer in a small 3 mm x 3 mm package. Coupled with the similarly small (2.5 mm x 2.5 mm) LPS25H 24-bit pressure sensor/altimeter by ST Microelectronics, and open-source Madgwick and Mahony sensor fusion filtering, this sensor solution offers 10 degrees of freedom, absolute orientation with quaternion, rotation matrix, and pitch/roll/yaw output. This board is intended as an add-on to the Teensy 3.1 microcontroller, whose powerful Cortex M4 processor running at 24/48/96 MHz can easily deliver 9 DoF sensor fusion filter update rates above 1000 Hz. The board can be soldered to pins 8 - 17 and utilize power and ground at the end of the Teensy 3.1. This allows sophisticated sensor fusion with plenty of pins left over on the microcontroller for power management, RF radio or bluetooth smart, or motor control shields, etc.

There are only pins broken out for 3.3 V and GND, SDA and SCL, and two interrupts, one for the MPU9250 and one for the LSP25H. The board is hardwired for I2C; even though the MPU9250 and LPS25H can both use SPI communication, I purposely chose to hardwire the MPU9250 for I2C because I wanted to minimize the number of pins taken up by this 10 DoF sensor solution. I designed the Mini Add-On so as to leave the hardware SPI pins free so other boards that absolutely require hardware SPI like RF radios or bluetooth smart could make use of them. With fast I2C (400 kHz), the sensor fusion filter rates are well above 1 KHz; this is plenty fast for all but the most demanding motion sensing and control applications.

Note: This board has a solder jumper for selecting whether to connect the 4K7 pullup resistors to the circuit. The solder jumper is useful if the mini breakout board will be used with other I2C devices that already have a pullup resistor in place, or if using with a microcontroller with internal pullups (the Teensy 3.1 has none). For I2C, one pullup on each of the SDA/SCL lines is enough; more than one is too much. Make sure you decide how to configure the pullups before you solder the board into place!

Why did you make it?

This is another example of the modular Teensy 3.1 concept with small, special-purpose add-on boards or shields that can be mixed and matched for specific applications. I originally began the project because I got interested in 9 DoF sensor fusion and my studies showed that ARM processors are the minimum required to get the full potential from open-source sensor fusion filters. Additionally, I wanted to create a small, portable, and lightweight device for motor control with robotics and quadcopters in mind as the application. The Teensy 3.1 has powerful ARM M4 Cortex processing capability with an Arduino-like programming environment. That means it is powerful, easy to use, and relatively cheap; you can buy them from OSHPark.com for $17. That's a bargain.

What makes it special?

This board is similar to the other Mini add-on boards I offer on Tindie but what makes this board different is the full-function pressure sensor. It comes with an interrupt so the microcontroller can be alerted on temperature or pressure thresholds, it can withstand up to 20x overpressure due to the unique pressure-sensing membrane design, it has an embedded FIFO buffer useful for data collection while the microcontroller sleeps or is busy with other tasks that can be burst read or used for averaging out noise in the pressure data, it has a variety of operational modes including a very low-power, low-noise mode where the claimed rms pressure resolution is 1 Pa with embedded filtering, or 0.01 millibar, and an absolute pressure accuracy of +/- 1 millibar!

This mini add-on board is typical of the small boards I make specially designed to fit on the Teensy 3.1. I designed, built, and tested them myself, and I use them for all kind of motion sensing and motor control projects. My plan is to add additional capability as I can. In addition to a variety of motion sensor solutions (this, for example), there is a modular Teensy add-on LiPo battery charger/power management board that connects to the first pair of three pins of the Teensy 3.1. There is an add-on board with dc motor control, one for gesture recognition, and will soon be boards with bluetooth smart (nRF51822), and RF radio (nRF24L01+). My goal is a small, portable (wearable), low-power device that can sense, communicate with, and control other devices in it's environment and last for weeks on a single battery charge. These small, high-resolution, low-power sensors make such a dream possible!

Order the board from OSHPark and build one yourself, or buy one from me and see how it works for you. Open source means you have options; I provided everything you need to do it yourself. I even wrote a well-commented sketch that runs on the Teensy 3.1 that uses many of the capabilities of the motion sensor and all capabilities of the pressure sensor, does 9-axis sensor fusion, returns yaw, pitch, and roll, and quaternion absolute orientation, and is ready for your use here.

Teensy 3.1 is NOT included with your purchase, but you can buy one here.