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Reverse Engineering the M6 Smart Fitness Bracelet

Following a year and a half of sitting inside the house, I set out to improve my wellbeing by getting a new fitness tracker. It worked out better than I expected - hacking on it kept me busy for a couple of months - at the small price of making me sitting inside the house even harder.

Before starting, I stated my goals as follows. I wanted to:

1. Understand its hardware
2. Figure out how to talk to it
3. Dump its stock firmware
4. Get it to run custom code, ideally making use of its:
- GPIO pins (both for input and output)
- Color display
- Bluetooth low energy (BLE) capabilities

I documented the process of going through these goals in the following sections. It’s been an incredibly fun journey. I hope you enjoy it as much as I did.

Disassembling the plastic case is so easy that it’s difficult to trust the IP67 water resistance rating claimed on the box.

Inside, we see some interesting stuff:

- A Telink TLSR8232 system-on-a-chip (SoC)
- A 0.96” (160x80 px) color display
- A tiny ~100 mAh LiPo battery and USB charging circuit
- A vibration motor
- A (most likely) fake heart rate sensor”

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