Over the last couple months I ended up losing two charging cases for the Redmi Airdots. I know what you're thinking, "how on earth did I end up losing the cases and not the buds themselves?". Both times the charging cases fell out of my pocket while driving. GET ZIPPER POCKETS PEOPLE!!.

Anyways, I either had to ditch the two pairs of earbuds which I already had or buy another pair of them. Yes, they don't sell the case on it's own. I decided to go ahead and make my own charging case.

Even though this instructable is for the Redmi Airdots, I'll provide extra info so that you can replicate it for other bluetooth earbuds. As you have probably guessed the project relies heavily on 3D design and printing skills, not to mention you need access to a 3D printer. You don't have to own a 3D printer, you can access at maker spaces, your university if you're a student.

Oh, make sure you take a look at the video to get an idea of the process I went through.

Supplies

Here are the parts I designed for Redmi Airdots

https://www.thingiverse.com/thing:4859105

You can use these for Redmi Airdots/Redmi Buds S.

For any other buds, you can design your own, follow the steps.

Tools:

3D Printer / Access to a 3D Printer
Digital Calipers for measuring
Soldering Iron and Accoutrements

Electronics:

A Li-ion Battery
TP4056 Li-Ion Charging circuit
5V Step up circuit
RGB LED 3mm or 5mm based on you case design
Magnets 5mm width, 2.5mm thickness
Spring Loaded pins / Pogo pins

Printer Settings :
Nozzle 255C, 0.16mm layer height and 110C bed temp, Blue ABS, Print Speed 40mm/s

Step 1: Identify If You Have a Smart Charging Case or a Dumb Charging Case

The first thing you need to do is identify the kind of charging case you have/had. If your buds have only 2 contact pads then it is a dumb charging case and you will be able to build a replacement for sure. If it has 3 or more contact pins then it is a smart charging case and probably involved in bluetooth pairing/connection process. I

This instructable is only meant for dumb charging cases.

If you have a dumb charging case continue with the instructable.

Step 2: Find Out the Polarity of the Contact Pads on the Buds

You can find it by just trial and error, most buds charge at 5v. You can use a 5v source to check which contact pad is positive and which is negative.

When you get it right, the light on the bud will light up.

Step 3: Desgin and Print All the Parts of the Case

You can either use my 3D models or design your own. Mine are custom to the size of my battery and the magnets I used.

My case is divided into 4 parts, the first one you see is the top cover.

The second one is just an insert which goes in the bottom of the third part and holds the charging pins and the magnets.

Third one is the middle part which hold the actual buds, the charging pins and the magnets.

Fourth one is the bottom part which holds the battery and all the electronics.

I have linked the thingiverse page in the first step.

I used ABS to print my parts since it is more durable.

I have listed the print settings at the start of the instructable

Step 4: Assemble the 3D Printed Insert and the Middle Part

This is what my version of the assembled insert looks like, the pogo pins are sandwiched between two magnets.

If you are not able to buy the pogo pins, you can salvage them from smart watch chargers. Be careful when removing them, they are very fragile and can easily break.

Make sure you put the magnets in the correct polarity so that the buds are attracted.

Once the insert is fully assembled, plug them into the middle part with correct orientation. You can use hot glue or an acrylic glue such as T7000 to hold the inserts in place.

Feel free to design your case/inserts differently so that they are easier to mount.

Step 5: Solder All the Electronics Together and Put It Into the Bottom Part of the Case

The circuit is pretty simple so I did not make a circuit diagram.

Battery -> TP4056 charging board -> 5V Step Up board -> Charging Pins

Put everything into the bottom case, I used some 3M tape to hold the components inside.

Make sure to align the USB port with the cut out on the print.

Step 6: Replace Charging Indicator LEDs on the TP4056 Board

There are two charging indicator LED's on the TP4056 board, you can replace these two with a single 5mm LED.

You can find out the polarities by using a multimeter.

This 5mm LED can now be inserted into the cut out in the 3D model so that charging status can be seen from above the case.

Step 7: Remove the LED on the 5V Step Up Circuit and Solder the Charging Pins' Wires to the 5V Step Up Board

This LED is constantly powered and will waste energy, you can remove this by using some solder.

Step 8: Assemble the Middle Part and the Bottom Part

Once you have soldered the charging pin wires to the output of the 5V step up board, you can assemble the top and the bottom part.

If you have designed your own case parts, you probably know how to go about bringing the case together.

Step 9: You're Done

Test for any problems.

These are the problems I had.

The pogo pins I bought had a high spring constant and needed more force to compress. I had a hard time in figuring out how much the pins should protrude out of the holes in the case.
The holes for the charging pins in the case should align perfectly with the contact pads on the buds themselves when inserted into the case. Even a 1mm offset will make the 3D print unusable. So, if you are designing your own case make sure you measure them accurately using a digital caliper.