These instructions will describe development of minimum viable product (MVP). We start from scratch so any tip or advance is more than welcome !

For testing different use cases, we have used Arudino, but for MVP we plan to make custom made PCBs. At the same time, we will also design several 3D models and the final design will mostly depend on the dimensions of PCBs.

The heart and brain of the bracelet is microcontroller , thus the first step is choosing the most suitable development system. Although Microchip has high-quality series of microcontrollers, we have decided to use cortex platform. Previous experience has shown us that programming is simple for MBED platform and that it has possibility of connecting with Keil debugger so we will use it for Vibhear. The idea is to make the prototype with MBED and afterwards to move programmed controller to a custom PCB. 

Well, let's start :)

Which cortex to choose from this boards ? 

M0 sounds like the best choice. We already have two development systems NUCLEO-F401RE with M4 cortex so we will use them and in the meantime, we will order a couple of M0 development plates. The priority is that the cortex does not increase bracelet production costs too much and that the stock is stable. 

Next, we will continue with power supply...

PCB design is completed. I'm using Altium/Circuit Maker. Take a look at snapshot . This is double layer PCB with component in each side and dimension 35x35mm.

We will use this board to test Cortex M0+ and other modules.