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ELPH skin

A flexible and low-power electrophoretic (e-ink) display worn on the skin, like a temporary tattoo.

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Epidermal electronics have been in development for several years; most devices are designed to collect biometric data to be displayed on an external device or use the surface of the skin as an interface for touch input. This project aims to develop a platform in which the skin's surface becomes the display itself.

I'm using a flexible e-paper display due to its low energy consumption, lightweight and micrometer-thin components, daylight readability and ultra wide viewing angle. The grayscale qualities of e-ink make it seem like an appropriate medium to mimic tattoo designs.

This project includes research and development of a thin and flexible multilayered PCB that can be produced with commercially available equipment. The PCB would then be bonded to a layer of silicone that temporarily adheres to the skin.

I’m completing this project during my Supplyframe Design Lab residency.

Design

exploded view


The face of the tattoo is a flexible e-ink display with the circuit board and power completely concealed underneath. All of this will be adhered to a layer of silicone with a skin-friendly adhesive. Note that this sketch is not to scale, the layers are all 2mm thick or less. It will be a challenge to get all of these components sandwiched together without shorting out.

I haven't determined power consumption but I will likely need to constrain features and framerates based on the largest capacity battery that I can find that's smaller than the physical dimensions of the display. I still need to figure out the connectors I'll need to recharge the battery but I do want to avoid using rigid materials here and throughout.

p363-kawahara.pdf

Instant Inkjet Circuits: Lab-based Inkjet Printing to Support Rapid Prototyping of UbiComp Devices

Adobe Portable Document Format - 7.71 MB - 03/09/2017 at 22:58

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  • One month in...

    Huntera day ago 0 comments

    This month went by too fast, I feel like I just got here.

    The deeper I dive into this project the more I realize how ambitious it is. I knew going in that it would take a small miracle for me to pull it off, as did Dan* and Supplyframe. But when I am locked onto an idea it’s difficult for me to be realistic. It’s easier to work harder than it is to adjust my expectations. My mind has a mind of its own. Must be an ego thing.

    System 2** is back online and it is feeling the pressure with 3 months left. I told Dan yesterday that I was going to start listening to him. He looked at me in disbelief and said, “Do you know how rare it is for me to hear that phrase?” I responded, “Do you know how rare it is for me to say it?”

    So, when you suspect that the ship is bearing too much weight, putting you and your precious cargo at risk, what’s the first thing you do? Unload some of your cargo in order to preserve the remainder. I’m putting the research & dev on a flexible circuit board on hold so that I can focus fully on hardware and software development. While the inkjet tests were fun and somewhat promising and I have so many more paths to explore with other materials (Kapton, Pyralux), and methods (silkscreen, lasercutting, chemical etching) I also know that it could take months or longer to come up with a robust and working solution to this problem, if it's even possible. There are manufacturers I can reach out to that have already developed a reliable and flexible (and multilayer!) circuit board and seeing how they do it may give me more ideas. But first, I need to design and build the thing.

    * Dan Hienzsch, Resident Engineer at the Design Lab

    ** Thinking, Fast and Slow, by Daniel Kahneman

  • Hardware Research

    Hunter03/21/2017 at 00:47 0 comments

    Plastic Logic's e-paper display


    There are several others before me that have attempted to drive TFT active matrix electrophoretic displays and have graciously documented their experience:

    Petteri Aimonen http://essentialscrap.com/eink/

    ED060SC4 display with STM32 microcontroller programmed with C

    Spritetm http://spritesmods.com/?art=einkdisplay&page=1

    ED060SC4 display with ESP8266 and PhantomJS pixel server


    David Guillen Fandos https://davidgf.net/page/41/e-ink-wifi-display

    GDE043A2 display with an STM32, ESP8266 and PHP

    Jara https://hackaday.io/project/1181-pip-watch

    GDE021A1 display with STM32 and Bluetooth


    j0z0r pwn4tr0n https://hackaday.io/project/10161-6-inch-pi-e-ink-display

    ED060SC4 display with Raspberry Pi

    Sapir https://hackaday.io/project/7443-e-ink-display-adapter

    ED060SC4 display STM32

    This week I am drafting some block diagrams and starting the schematics for the power management circuit while I wait for my test displays to arrive. Reading about how these displays work is fascinating. There's something about their appearance that feels not quite digital and that's due to the millions of microcapsules of ink that are charged with 15V and -15V source voltages. The displays I'm considering have a TFT (thin film transistor) array just like LCDs. Each pixel is attached to a transistor and capacitor that store the current state while the other pixels are being addressed. The image is retained even when all power sources are removed.

    As of now my plan is to use a flexible display (Plastic Logic's or E-ink) with an ESP8266. At a minimum, I'd like to be able to update a bitmap image wirelessly, ideally I would like animation or write a program that draws to the screen directly. All of this will be highly dependent on power consumption and the amount of time I have. We'll see how far I get during my residency, but a functioning prototype with all electronics integrated into a single on-skin device is my primary goal, no matter what path I take to get there.

  • Materials Research

    Hunter03/20/2017 at 08:25 0 comments

    a few of the papers I reviewed and test plan notes

    I've been switching back and forth this week between development of the flexible circuit board** and designing the driver board hardware so I am wading in white papers and data sheets. I'm just a one-person team but parallel pathing this project is necessary since these two streams depend on each other. Research is by far my favorite part of the process, there's a lot of uncertainty about whether or not my design will work. I also learn a lot of interesting information that is completely irrelevant to my project. I'm a diligent procrastinator.

    I've converted an inkjet printer to become a circuit printer and after reading some research from others who have attempted the same or something similar, I have some ideas on what to test and measure and techniques to get better quality prints. I'll be sharing some photos of the conversion and results from the testing in my next post.

    I also learned about how rigid circuit boards are made and it's a pretty wasteful process. One of the reasons why I chose inkjet over other flexible circuit options is that it's an additive method and generates less waste. It's also very fast. Theoretically. Since we have an Othermill CNC here in the lab perhaps I can pit the two processes against each other. If I do I'll broadcast it live.

    ** using the word "board" when referring to a flexible substrate is a contradiction; I need to come up with a new descriptor

  • First shipment!

    Hunter03/09/2017 at 22:56 0 comments

    Got my initial shipment of supplies that will enable me to rapidly prototype with printed circuits. I will be using an inkjet printer to extrude silver nanoparticle ink so that I can print traces onto thin transparent film. Several layers of this film sandwiched together will form the circuit for my display driver.

    I'm using the research paper "Inkjet Printed Circuits" as reference for best practices for inkjet printed circuits.

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