Enclosure Design
The enclosure housing the electronics for GaitKeeper went through several design iterations to arrive at the most aesthetically pleasing and comfortable implementation.
Iteration 1
Iteration 1 of the design was merely a concept of how the enclosure would look with placeholder dimensions. In later iterations, the design would be scaled according to the ankle circumference of a 95 percentile male.
Iteration 2
Iteration 2 of the design was an improvement on iteration 1 with a two-part design; base and lid. Both parts were scaled to fit a nRF52 development board, MPU6050 IMU board, and a 1200 mAh LiPo battery. In addition, the two parts were designed to be fastened together by four M3 countersunk screws.
Iteration 3
Iteration 3 of the design was scaled to enclose a nRF52 development board, MPU6050 IMU board, a prototype board and a 1200 mAh LiPo battery. In addition, mounting pads were designed for all the boards, so that they could be fastened to the base of the enclosure with self-tapping M2 button head screws. The clip on the inside was extended so that two ankle straps could be used for more precise fastening to the user's ankle. The length of the enclosure was extended and rounded at the long edge for aesthetics and improved resistance to water ingress. Finally, a hole was cut out of the enclosure for the wire harness that routes to the pressure sensors positioned in the user's insoles.
Iteration 4
Iteration 4 was a complete re-design with a focus on sleek appearance and portability. The goal was to make an enclosure that hugs the ankle tightly, so that it could fit under pant legs without being a bulky eye sore. The flat design has two flanges angled at 45 degrees with each face housing a different electronic board. Altogether, the design encloses a nRF52 development board, RTC+SD board, perfboard, MPU6050 IMU board, and a 1200 mAh LiPo battery. Similar to the last design iteration, each board is secured to the base of the enclosure with self-tapping M2 screws. The battery is sandwiched between the base and lid of the enclosure where even face pressure is applied to the cell when the two parts of the enclosure are fastened together. This face pressure plus isolating walls constrains the battery in all directions. A microUSB port was added to the base for easy connection to the nRF52 to provide rapid programming and testing. In addition, two holes were cut out of the lid for an easy visual of the indicator LEDs on the nRF52 development board.
3D Printing
The enclosure base was 3D printed on an Ender 3 with dark gray PLA.
The nRF52 development board, RTC+SD board, perfboard, and MPU6050 IMU board were fastened to the base with M2 screws, which self-tapped into the PLA holes.
Remarkably, the PCB stand-off holes and Micro USB cutout all fit perfectly!
