Karhu Active Pulse teardown

Karhu Active Pulse (W311) was a fitness tracker product that was sold cheaply few years ago. It was quite comfortable on the wrist the UFit application running on Android was just fine (not very good or bad).


Most functions go on by pressing that white circle (pulse, sleep monitoring) for about three seconds. You can scroll through the functions by pressing the white circle. The bracelet has that picture of the sun and the moon. When you press the button on the wristband for about 3 seconds, the night mode switches on and sleep monitoring starts. In the morning change the mode back to the day ..

The product was very light and quite comfortable on the hand. It used a custom charging cable for charging. The mechanical construction could have been better, it broke down quite easily: did not properly charge and the clear plastic over the display fell off causing some other damage to inside electronics.

Let’s look inside the device.



The main components inside device are nRF51822 Bluetooth Low Energy and 2.4 GHz SoC, display and LiPo battery.

The nRF51822 is a general purpose, ultra-low power SoC ideally suited for Bluetooth® Low Energy and 2.4 GHz proprietary wireless applications. It is built around the 32-bit ARM® Cortex™-M0 CPU with 256/128 KB flash and 32/16 KB RAM. The flexible 2.4 GHz radio supports Bluetooth Low Energy and 2.4 GHz proprietary protocols, such as Gazell.


Karhu Pulse W311


1 Comment

  1. Tomi Engdahl says:

    Becky Stern, David Cranor, And A CT Scanner Vs The Oura Ring

    If you wonder how it’s possible to fit a fitness tracker into a ring, well, you’re not alone. [Becky Stern] sent one off to get CT scanned, went at it with a rotary tool, and then she made a video about it with [David Cranor].

    While it’s super cool that you can do a teardown without tearing anything down these days — thanks to the CT scan — most of the analysis is done on a cut-up version of the thing through a normal stereo microscope. Still, the ability to then flip over to a 3D CT scan of the thing is nice.


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