How to Build a Smartwatch: Picking a Chip

PebbleOS isn't the only player in this space. There's also https://www.espruino.com/ which powers https://banglejs.com/. It's a tiny implementation of Javascript for microcontrollers, so it's really easy to hack your device in real time.

It also powers the Fallout Pip boy and possibly some other stuff from the wand company: https://www.thewandcompany.com/fallout-pip-boy/ See: https://github.com/orgs/espruino/discussions/7577

"The SDK is open source" Oh, a BLE MCU with open source code SDK?

AFAICT, the BLE code is provided as a binary blob. https://github.com/OpenSiFli/SiFli-SDK/tree/6c82a9b15db49871...

Which isn't a problem. But, I wish if something is described as "open source", you could read the source code for it.

This smartwatch isn't really all that smart by today's standards.

I would really miss the mod cons I have on my current smartwatch. Payments over NFC, dual-band GPS tracking, 4G LTE connectivity. The Pebble (and repebble) trades all that in for a multi-week battery life. But the minor hassle of once-every-two-days charging on my galaxy watch really isn't enough to forego all these powerful features for me.

More information on the chip here: https://www.cnx-software.com/2025/05/14/sifli-sf32lb52j-big-...

Interesting they did not go with 2-chip design(1 for main application, 1 for BLE stuff). Which is sometime makes sense because high power mcu usually does not have RF

Glad to finaly see someone in the low-power chip industry going in the open source direction. Thanks for the insight!

When I saw rePebble be announced, I signed up for it right away. Only later I realized I actually don't want a smartwatch, I want a dumb watch with vibration notifications.

I know I'm in the minority, but it's a niche that has a few very interested people in it [0] [1] [2]

After wearing the Casio F105 for the past 2 years, I can't go back to something larger, heavier or thicker than this. I could accept weekly battery charging for the benefit of having some bluetooth functionality.

So nowadays I'm looking for a super small bluetooth chip that can power a small vibration motor, which can receive all notifications from my iPhone. I would like to glue that chip, motor and a small lithium battery between the two straps of my F105, because in my tests it seems I don't notice if I add a small weight there.

I still remember when I first used my first Mi Band 1, a forgotten fitness band that had no display, just 3 RGB LEDs that could even get specific colors based on the app that sent the notification. I could know right away when I got a blue Messenger chat that I needed to answer now, or a yellow Google Keep reminder that I could ignore until I got back to my computer.

[0] https://www.reddit.com/r/pebble/comments/9xw2j2/im_looking_f...

[1] https://www.reddit.com/r/smartwatch/comments/174hq9x/need_a_...

[2] https://tildes.net/~tech/18nf/smartwatch_primarily_for_notif...

I started to hack around cheap chinese Freqchip SOCs:

https://github.com/zoobab/FR801xH

You could get smartwatches for 3EUR on Ali with this chip.

Thank you for the write-up. Cool to see some degree of open-source hardware running PebbleOS.

Though, can we stop having left-aligned blogs in 2025? Wide screens have been here for a while, it makes it unnecessarily hard to read :(

Love this write-up. nimBLE is a great bluetooth stack; this should open up some interesting opportunities for Core Devices moving forward.

> The most interesting and difficult constraint is actually software compatibility.

But it is probably the easiest constraint to get around. I would put this one more towards the end of the list.

@ericmigi these are great BTW, wish you did them during YC while we were going through all these decisions haha

Awesome feature set for that price.

[flagged]