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oled earrings

Display falling tetris blocks on a oled screen made into an ear ring. It's powerded by a coin cell.

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oLED earrings.
An oled display shows various falling tetris blocks. A simple stainless steel hook makes it wearable on the ear. It is powered by a rechargeable lithium coin cell.

This year I had a special gift for my girl. Earrings that feature an oled screen with animations of her favorite arcade game, Tetris. The original idea was to have tetris blocks fall from the top of the screen to the bottom and stack up. But in the End I had to settle with a simple scrolling animation of tetris blocks.

It uses a rechargeable lithium coin cell (LIR2032) to power a oled screen and an ATTiny85 micro-controller to control the content displayed.

Once the power switch is flipped the display initialized and cleared. Then the tetris blocks are drawn in a predetermined pattern. The display is set to auto scroll top to bottom and finally the microcontroller enters deep sleep without any way to return.

Github: https://github.com/HKay/oled-earrings
Youtube: https://www.youtube.com/watch?v=d6km96m5RsY

  • 1 × Atmel ATTiny85 microcontroller to initialise the display
  • 1 × oled screen at 128x32 pixels to display the falling tetris blocks
  • 1 × LIR2032 rechargeable lithium-Ion battery power the project with 3.7V and 20mAh
  • 1 × Coin chell battery holder make coin cell fast swap possible
  • 1 × Switch bring current to 0 when earring is not in use

View all 6 components

  • The disenchantment

    Daniel12/31/2017 at 16:23 0 comments

    She really liked it!

    But after wearing it for an hour it turned out to be too heavy.

    At 9 grams one earring isn't exactly light but I have seen women wear heavier jewelry. So I have to go back to the drawing board. She wouldn't let me obsess over such a thing so I have to do it in secret... again.


    This time I'll ditch the prototyping look and make a proper PCB without the extra PCB the display comes with.

    It also should feature a way to detect a low battery situation to prevent accidental deep discharge of the battery.

    I even want it to be charged without removing the battery. The display could display the current charging state of the battery while being charged.

    The content of the display should be properly randomized.

  • The plan

    Daniel12/31/2017 at 15:51 0 comments

    This year I had a special gift for my girl. Earrings that feature an OLED screen with animations of her favorite arcade game, Tetris. The original idea was to have tetris blocks fall from the top of the screen to the bottom and stack up.

    The display I had. It was cheap on amazon and had the right dimensions 128x32 pixels. Turned upright it approximates the tetris screen and has a good point of mass to dangle like earrings are supposed to.

    The micro-controller was also easy to pick since there is only one small micro-controller I already worked with. The attiny85. This one I also had in abundance. November already had started so time was short. Not enough time to find and learn to use another candidate.

    But the critical part was power. A coin cell is an obvious choice but heavy and bulky. Also there is the issue of producing waste. This was not an option since my girl would dislike a present that would burn through a coin-cell a day. Also there is the issue of the display requiring a minimum of 3.3V. Coin cells usually have 3.0 Volts. Fortunately there are rechargeable Lithium-Ion coin-cells with a voltage of 3.7V. This completely solves the waste and voltage problem at the same time. However the sizes to choose from are very limited. The target wear time is 10 hours. A full work day. With the smallest battery the LIR2016 @ 12 mAh that would result in a current budget of 0.6 mA to not deep discharge the battery. Very optimistic looking back. However there was always the way to go to a LIR2032. It fits in the same battery holder.

    Fast forward a few weeks the code worked fine on an arduino clone board which I used for prototyping. Measuring the animation foiled my plans to have a stacking animation. The display alone required 1.8 mA of current at 3.7V. The ATTiny85 would also require 1mA when i kept it running to calculate the falling and interaction of blocks. This means I had to use the biggest Lithium battery available the LIR2032 with 40mAh. And it still wouldn't be enough. The power budget for that battery is 2mA of continuous current. The micro-controller has to be in deep sleep as long as possible.

    Turns out the SSD1306 has a auto scrolling feature. This comes in handy. That way the micro-controller isn't required during runtime at all. It only has to do the initial setup of the screen and start the scrolling animation.

    In December I ported the software to the ATTiny85. Never did I2C on that platform but how hard can it be? Well, turns out the universal serial interface of the ATTiny85 has next to no features. This cannot be a strait port by renaming a few registers. With the deadline looming I decided on soft I2C. It didn't have to be efficient to set up the display and go to deep sleep.

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Discussions

magnets wrote 01/23/2018 at 22:46 point

you can save a bit by not having a switch, use the weight of the earing hook to pull the power connection high maybe? So it's only on when dangling...

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mayank shukla wrote 01/11/2018 at 05:29 point

Using Flex PCB can reduce the PCB weight and also size.

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Ethan Schwartz wrote 01/10/2018 at 23:33 point

Very cool project!, and interesting use of the scrolling feature in that display.

Too bad they are a little heavy--As you said, a proper PCB will let you ditch some weight, maybe a soldered metal tab battery holder would be lighter too?

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Daniel wrote 01/15/2018 at 22:05 point

The battery ist responsible for most of the weight. Sure the next version will feature a SMD battery holder but that wont save much. Also the PCB size is just too small to really add to the weight.

Lithum polymere is even heavier. My best option is to get a really small battery such as used in wireless earphones. A supercap with an energy harvesting IC might be worth exploring too.

As long as it's proteced against under voltage a short lifetime will be ok. The parts are so cheap a second pair for changing when the first runs out is reasonable.

The most expensive part of the christmas present was the himitsu bako box it came in.

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