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WS2812B (Neopixel) Earring

Earring with 16 addressable LEDs (WS2812B-2020) and rechargeable coin cell battery.

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My new ongoing earring project with addressable LEDs.

Main features:
- 16 PCB edge mounted WS2812B-2020 LEDs
- ICs mounted 90° for small earring diameter
- rechargeable Li-Ion battery "inside" the PCB
- ATtiny 45 running Neopixel library
- 3.6V booster converter
- button for animation selection

PCBs sponsored by PCBWay.

This earring is the result of an idea integrating a rechargeable coin cell in the middle of a circular PCB and placing LEDs and components around it. To minimize the overall earring diameter, LEDs and other components are mounted to the edge of the PCB by placing the pads on the top and bottom layer of the double-sided PCB. The edge mounted LEDs making the LEDs visible from all sides and giving a nice round light effect. Also it’s possible in the future to add some diffusor around the earring.

This project is work in progress and the shown pictures are the second iteration of the PCB after a first proof of concept. Tested battery life is at least 2 hours with a continuous animation.

Sponsorship PCBWay

The PCBs of this project where kindly sponsored by PCBWay. Quality is outstanding, especially with the tight tolerances for the milling of the in- and outside to ensure a perfect battery fit and the easy soldering of the edge LEDs. Check out their website!

  • 16 × WS2812B-2020 LED
  • 1 × ATtiny45 Microprocessors, Microcontrollers, DSPs / ARM, RISC-Based Microcontrollers
  • 1 × 1254 Li-Ion 3.7V Coin Cell
  • 1 × TPS613226ADBVT Boost converter
  • 1 × WE 74438335047 Inductor

  • Power supply

    makeTVee08/08/2022 at 10:45 0 comments

    The earring was designed around the 1254 Li-Ion battery which is a good fit between size (12mm diameter, 5.4mm thickness) and capacity (around 40-60 mAh depending on manufacturer). First tests with a LIP1254 showed two major issues, the battery capacity was way lower then expected when discharging the battery with 5-6mA and the voltage was dropping way to fast under 3.6V which was below the forward voltage necessary for blue LED on the WS2812. So after approx. 10-15 minutes, only the red and green LED light up. Not sure what caused this behavior, maybe the cells where already quite old or discharged deeply.

    The solution for the voltage dropping was adding 3.6V boost converter TPS613226ADBVT to the ring. This boost converter and the necessary inductor are mounted on the inner edged inside matched cut out areas. 

    Because the battery didn't worked like described in the datasheet, it was replaced with a more expensive Varta CP1254 which not only fulfilled the datasheet spec and lasts more than 3 hours@5mA, but also showed a much lower voltage drop so it has to be tested, if the boost converter is really necessary and useful for the next revision. Also other cells from different sources will be tested in the near future to find alternatives.

  • PCB and assembly

    makeTVee07/19/2022 at 15:06 0 comments

    The PCB has a center hole and some cutouts for the components.

    The LEDs are placed first using a resin printed jig. Matching holes are holding the LEDs in place while soldering one side to the PCB. 

    When all LEDs are soldered to the top

    the PCB is removed from the jig and the bottom side is soldered.

    The ATtiny 45 is solder in a notch of the PCB in 90° orientation by using two resistor nets (10 Ohm), one per side.

    The booster converter with the inductor are also solder 90° with corresponding pads on top and bottom layer. If the battery voltage drops below 3.6V, the blue LEDs of the WS2812B stop working, therefor the booster is used to ensure a proper voltage level.

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Discussions

g.sabino025 wrote 08/16/2022 at 20:16 point

The design of the pcb is ingenious. I've been looking how to make led earrings for a while but I was always stuck on making it compact but the way you did it was incredible. From the side mounting led and attiny45 to the battery holder while still making it look good. Simply beautiful!

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James Micciche wrote 07/28/2022 at 20:51 point

Super-impressive design, love the side mounting idea, it not only gives a really unique look but is integral to making this project work.

Would love to see a more complete BOM, I'm especially interested in which boost converter and related component values you're using.

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makeTVee wrote 08/07/2022 at 15:38 point

Thank you, I have updated the BOM, will also add some details in the project log.

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Ben Hencke wrote 07/20/2022 at 20:33 point

Very cool! Impressive sidemounting!

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