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Charger for my fitness tracker watch Answered

I've lost my charger for my mykronoz fitbit 4 watch, and there isn't any available online for purchase, is it possible to make one myself? https://m.imgur.com/a/C21txXu

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Orngrimm
Orngrimm

Best Answer 11 months ago

Sure. What you will look for are so called "Pogo-pins" of "Springloaded contacts". Like https://www.mouser.ch/Test-Measurement/Test-Equipm...
Hint: Those can often be salvaged from electronics where a battery is connected from like an older smartphone.
3D print a nice cradle with the holes @ the right place and you are left with the electronics of the 3 contacts to connect to. (More to that later).

I added a picture of a programming-jig i made just like it, but with (mostly) pointy Pogo-pins.

Normally, the voltage is 5V as it comes from USB. All Smartwatches i know and owned/own have 5V in.

Now to the "what to feed it?"...
Here is a little trick for you: The FCC.
If you want to sell anything which has radio, you need to certify it at the FCC. And they are a public entity so the reports and stuff are free and open (Mostly). Unfortunately the schematic is not open to the public :(
https://fccid.io/2AA7D-ZEFT4H
Bam!
And https://fccid.io/2AA7D-ZEFT4H/Internal-Photos/Int... EUT photo 4 shows clearly the + and - of the 2 pads. The 3rd pad seems to have an "R" labeled. That would be a thermistor to sense the temperature of the LiPo during charging.

So: I would test and supply +5V to the center Pin and GND to the left pin if viewed from the bottom.

As a sidenote: Photo 10 shows some very interesting testpoints to access the watch for hacking! :)

If you find an answer specifically good and it answers your questions, it is a nice thing to select it as best answer to honor / "pay" the autor ;)

2020-05-14 09.49.35.jpg
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Jack A Lopez
Jack A Lopez

Answer 11 months ago

Nice work finding those pictures of this artifact, in an FCC report, and identifying the pins.

I was looking looking for documentation for this gizmo, official and unofficial, but was stymied by the fact that there are so many versions of Fitbit (r) out there.

Although I did notice most of them want 5 volts DC to charge from, and I think there exist aftermarket charger cords, with USB plug on one end, and these funny little pressure pins on the other end.

But again, I could not figure out where this particular one, that OP showed us, fit into the family of these gizmos.

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Orngrimm
Orngrimm

Reply 11 months ago

Thanks!
Yeah... I was too quite puzzled by the plethora of FitBit's out there... A bit of googling lead me to partially wrong answers and then i just flipped the table and said "Fcc. If not them, who else?".
Took me again a bit of google-fu, to realize that the compay is "kronoz".
"FCC kronoz" as search yielded the page of FCC where all the kronoz-Devices are listed. Quite simple to find the abbreviation for the fitbit4 of kronoz there. From there on it was really smooth sailing.
It would be even easyer if we could read the FCC-ID in the foto at the top. Unfortunately, the image is not too sharp there...

So yeah: Knowing the FCC-page could help a lot of people to identify stuff.

Have you seen the well labeled testpoints on this device? Man! It is almost worth buying one just to mess with the Serial and SPI and all the goodies labeled there...

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Jack A Lopez
Jack A Lopez

Reply 11 months ago

I see those labeled test points, but I am kind of at a loss for what to do with them.

I might as well put a picture of them here, for anyone else who wants to look at them.

kronoz-fitbit-board-test-points.pngfitbit-board-front-chips.png
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Brief_bright
Brief_bright

Reply 11 months ago

The kind of answer I've been looking for.. ✌
I've searched the whole web for an answer to identify those pins and here I am..


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Orngrimm
Orngrimm

Reply 11 months ago

Thank you!
Easy. Thats why there ARE such websites as here to ask such questions. :)
I learned the trick to get good pictures from electronical devices (Even if not yet released sometimes) thru the FCC from Hackaday.com. That and ifixit if the device is widespread and on the expensive side.

I hope you remember this website (FCC) in your next hunt for electronical identifications :)

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handypat.sa
handypat.sa

11 months ago

You can make a plan.

These types of watches normally use a standard 5V 1A cellphone charging adapter.

First off, you will need to find out which of the 3 contacts on your watch are the positive and negative terminals.

Find a spare cellphone charging cable, cut the small end off and carefully strip about 30 mm of the outside insulation off. This will expose either 2 or 4 wires. You will now need to find which wires are the positive and negative wires carrying the 5 volts from the standard cellphone charging adapter.

Using some form of tape, stick the positive lead onto the positive terminal and the negative lead on the negative terminal on the watch. The watch should begin to charge.

This is the quickest way to solve your immediate dilemma and "read as" a temporary solution until you find your original charger, purchase a new one or come up with a permanent solution.

I hope this helps you.

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Brief_bright
Brief_bright

Reply 11 months ago

Thanks man for the reply :)