How to Build a Smartwatch: Picking a Chip

Summary

VIDEOFull video of this post is up on my podcast on YouTube! Subscribe on PocketCasts, Spotify, or Apple Podcasts. TLDR:We've selected a chip for Core Time 2 - SF32LB52J. It’s from a company called SiFli, and features an open source SDK.I’m writing a series of posts on how to make a smartwatchCovering how to pick a chip (today), other hardware and software stuff (later)I hope others will use PebbleOS to build interesting new smartwatches and other devices!This is the first in a series of posts around the steps you need to take in order to build a smartwatch. I want to show that it's not actually that hard to make a decent one in 2025! Hopefully the work that we're doing to make these new watches will help other folks to build some as well. Smartwatches are not and should not be ‘one-size fits all’ devices. I really hope that the open sourcing of PebbleOS might spark someone’s imagination and enable them to build a smartwatch that fits their needs perfectly!A smartwatch is a system made up of three main components: Watch hardware (this is the actual watch itself)Watch software (usually referred to as the firmware or operating system)Mobile companion app (iOS and Android app that sends notifications, downloads watchfaces etc)As I've mentioned before, designing a consumer electronics product like a smartwatch is an exercise in constraint maximization. You need to identify a target experience goal (”I want a smartwatch with an always-on daylight readable display that lasts for 30 days”), then break that down into features/specifications (”e-paper display”, “Bluetooth LE”, “water resistant”, “$150 retail price”) and then create a design with hardware and software components (”Sharp Memory LCD”, “150mAh lipoly battery”, “FreeRTOS” etc) that meet your specifications and fulfill your goal. After almost 20 years of building products, this process comes naturally to me - sometimes unprompted! I can look at any product and picture the exploded view, estimate manufacturing cost...