Have you considered using a puck? You might have enough io pins and it has the coin cell as is already round like a watch?
@Wilberforce started
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
Have you considered using a puck? You might have enough io pins and it has the coin cell as is already round like a watch?