DIY magnetic charger for Kingwear, Lemfo, Domino smart watches and how to avoid buying the wrong cable

Jul 20, 2017

Within hours of receiving my first Android smart watch, I managed to loose its charger cable.
To add to the back luck, the replacement I ordered turned out to have a different pin out.
The information below should help to both avoid making the same mistake and otherwise turn the mistake into a compatible charger.


Let's start with the standard pin out of a type A male USB connector (colors are only indicative and based on the cable I used, for conventional color coding, refer to https://en.wikipedia.org/wiki/USB#Pinouts)


My mistake was to assume that any device using the same "4-pin USB magnetic charging cable" would use the same pin out.

The cable I received was in fact for the Pebble Time watch, which uses a different layout (D-,GND,5V,D+) while the MTK6580-based watches like Domino DM368, Lemfo LES1, Kingwear K88H would just observe the standard USB format seen above with power wires on the edges (GND,D+,D-,+5V).

The exact pin-out can be verified by opening (gently, don't break the flat cables!) the back cover of the watch...(something I should have done that in the first place)



I temporarily converted the Pebble cable into a MTK6580-compliant charger by doing the following: 

- Carefully cut the plastic around the magnets until you can push the  "pogo pins" out of their cavities


- Detach/cut the original wires, they are too thin to work with anyway.
- Sacrifice an old USB cable to cut and expose its 4 wires within the shielding.
- Solder the extracted pogo pins to each wire. Some "Helping Hands" clamps might be needed here.  






- First, check how the magnets snap on the watch, and then insert the pins back in to their cavities following the correct USB layout. Here I only wanted to charge the watch while I'd get a proper cable, so I didn't bother with the data pins. 






- Try the cable on a USB power source. I suggest a smart USB charger or at least use a USB tester in between to check the current. If the battery is completely flat the watch will only show signs of charging after a few minutes. The USB tester reading will tell immediately if the connection is working. 



- Finally, protect the wiring and the connector with some electric tape.



This is only a temporary solution and purchasing a (couple of) spare compatible cable(s) is by far preferable. Avoid cables with mention to Pebble or Asus ZenWatch 2.

The Domino 368 has a particularity that resides in the magnets being swapped, so, while being compatible in wiring, the spare cable I ordered from China ("for K88H") would require some DIY as well to re-locate the magnets.
The right charging cable would be specifically labelled for D368, LF16, or DM98.
The official Lemfo web site has a complete choice of cable per model (for DM368, select LF16).







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