OpenShoe

The cas­ing STL files can now be found under:
Sys­tem repro­duc­tion
The cas­ing is 1.5[mm] thick all around.
The outer dimen­sions of the cas­ing are 23.2x31x13.5[mm].
The cas­ing has a snap fit solu­tion and does not require any screws or sim­i­lar. This far, we have had the cas­ings printed on a Maker­Bot 2 by myobjectify.com.

Below is a brief tech­ni­cal sum­mary of the new boards/modules

• 4 MPU9150 9-axis IMUs sam­pled in parallel
• Atmel AT32UC3C2512C 32-bit float­ing point microcontroller
• ST SPBT2632C2A Blue­tooth module
• Bat­tery pow­ered with charg­ing via USB
• 4 layer 22.5x20x5.5mm PCB (exclud­ing pro­trud­ing USB connector)
• Mod­ule size, includ­ing 150mAh bat­tery, circa 31x24x14mm (cas­ing not final)

In addi­tion we have also thrown in a flash mem­ory (up to 64Mb) and a pes­sure sensor.

If you have looked at the pho­tos below you may be won­der­ing why there are two micro-USB con­nec­tors. The one which has a slot in the cas­ing is a proper USB used for com­mu­ni­ca­tion (if you don’t want to use the Blue­tooth or sim­ply want more data than the Bluetooth-link can han­dle), charg­ing, and repro­gram­ming with the boot­loader. The one hid­den inside the cas­ing actu­ally con­tains a JTAG inter­face for debug­ging and repro­gram­ming. Micro-USB con­nec­tors are sim­ply con­ve­nient small foot­print connectors.

Since we finally got a mod­ule work­ing, I have now pub­lished the PCB design files under

- Sys­tem reproduction

Basic embed­ded soft­ware for the new mod­ules is already avail­able on source­forge. How­ever, sig­nif­i­cant updates, espe­cially to the wire­less inter­face, is expected in the near future. The STL-files for the cas­ing I will pub­lish as soon as it has gone through some more iterations.

By the way, the new boards goes under the name MIMU22BTv2 (MIMU=multi-IMU, 22=number of IMUs on front and back, BT=Bluetooth, v2=version 2). This is how it’s referred to in all config-files in the software.

Note that for some fea­ture such as the mem­ory and the pres­sure sen­sor there is still no soft­ware sup­port for and they have not been tested at all. On the other hand they are not nec­es­sary for the core func­tion­al­ity or the boards, i.e. pedes­trian tracking.

After what feels like a 1000 mount­ing attempts, we finally made one board of the first gen­er­a­tion work! So 4 IMUs, wire­less trans­mis­sion, bat­tery pow­er­ing and real­time step­wise dead reck­on­ing. To say the least I’m pretty relieved to see the whole chain work­ing. We are still expect­ing updated ver­sions of the boards but there are (should be) no changes to the schematic so hope­fully they should work right out of the box.

The bat­tery cables should later on be sol­dered straight into the board but due to fur­ther test­ing needs we didn’t want to do that. Con­se­quently, you see the ugly solu­tion with a JST con­nec­tor and a pin header, and for the ini­tial test­ing we had to go with elec­tri­cal tape instead of the cas­ing lid.

Above you see the first (actu­ally sec­ond, since the first time I got about 5m and then the bat­tery cable came off) track­ing result with the unit taped to the fore­foot and walk­ing back and forth in the cor­ri­dor two times. Note that Mat­lab is only sum­ming up the step dis­place­ments and head­ing changes and most of the pro­cess­ing is done in the module.

Plenty of things remain to be done but at least now we know we will even­tu­ally have work­ing modules!

While wait­ing for the new boards we have also started work­ing on the design of the cas­ing for the new mod­ules. Sur­pris­ingly num­ber of details to think about! Cur­rently we are con­sid­er­ing a snap-fit solu­tion. A cou­ple of guys from myobjectify.com helped me with the cad and print­ing. The day before yes­ter­day I got a first crude print in my hand. The pho­tos above show the size of the cas­ing in com­par­i­son with an older unit and the cas­ing with a bat­tery and a par­tially assem­bled board in it (used for test­ing the wire­less links).