Modular Teensy Project
I am creating modular add-on boards (AKA shields) for the Teensy 3.1 with either Invensense's MPU9250, ST Microelectronics LSM9DS0, and Bosch BMX-055 9-axis motion sensors all coupled with either Freescale's MPL3115A2 or Measurement Specialties MS5637 altimeters/pressure sensors. The intent is to gain 10-DoF motion sensing capability using open-source Madgwick/Mahony sensor fusion in a very small package. The modular approach allows other capabilites such as Bluetooth Smart, power management (battery charging), and motor control boards to be added to the same Teensy to provide flexible configurations tailored to specific applications.
I have reached the first milestone by successfully designing, assembling, and testing a board with the LSM9DS0 motion sensor that is attached to the pads on the back of the Teensy and functioning. Here is what it looks like:
Top left is the bare PCB I had made at OSH Park. Bottom left is the populated board with passive components (don't look too closely at the bad solder job!) and the LSM9DS0 9-axis motion sensor. This was only my second solder reflow experiment and the first really successful one. The big board on the right is the Teensy 3.1 available from OSHPark.com for $17---a steal for an easy-to-use Cortex M4 ARM processor. The idea is to mount the sensor board on the back pads of the Teensy to provide absolute orientation without tying up, well, any of the pins one would normally be using.
Here is what the final product looks like mounted onto the back of the Teensy 3.1. Yes it hasn't been soldered yet in this picture but, trust me, I soldered it and it is working well.
The picture is poor but you get the general idea.
It turns out there is a specific problem with the design of this board that I discovered after it was sent to the fab. One of the interrupts was broken out to pin 33 of the Teensy 3.1 This pin has several non-digital IO functions including toggling between boot modes. So, bottom line, it really cannot be used as a GPIO pin as I have done here. Fortunately, I learned this before I soldered this pin so the board still works, just without the use of this interrupt. I am in the process of redesigning the board to re-route this interrupt elsewhere, which should be easy to do, but requires another OSHPark board order. So the first demsonstration of the modular Teensy concept is a success.
More adventures with the modular Teensy project to come...