An input device based on tapping your thumb on to the phalanges of your fingers

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When idle, I often find myself fidgeting, tapping my thumb to the inner sides of each finger in a random pattern. I thought, why couldn't the tapping mean something? It could become a convenient and discreet way to type out messages, a new language. This project aims to explore how I can make an input device that can make sense of these gestures and turn it into something useful.

This could be easy to do using gloves, but I ultimately want to do it with bare hands only, nothing else. At first, I will be using capacitive touch to make a proof-of-concept of this and afterwards combine machine learning and EMG to make it bare-handed - no gloves, no cape required!

The idea is simple - create an input device that relies on tapping your thumb against the inner sides of the fingers - the phalanges. Keeping the thumb independent and free to move, it has (4 fingers) * (3 phalanges per finger) = 12 combinations of a single tap gesture. Multiple taps can increase the number of key combination possible. I have the key mapping open-ended for now, but I am open to ideas.

I foresee this project to be useful both for non-differently abled and differently abled people.

I will create the first prototype for this project using capacitive touch sensing on a flexible PCB substrate mounted on every finger. If and when this is proved, the next challenge will be to do this without wearing anything over the finger.

The device would connect to the computer/mobile/tablet using either USB HID or BLE. Both are well-established for the purpose and the challenge I see is in making the sensing work.

  • 1 × Capacitive sensor flex (custom board)
  • 1 × Teensy-LC or Teensy-3.2

  • Chalking out the Proof of Concept

    Kumar, Abhishek05/05/2019 at 09:23 0 comments

    First, a picture of the concept:

    The flexible substrate fits over the finger using three rings created by folding the ends of the PCB over to form a ring. The arrangement of the electrodes here is such to create both the sliding as well as the touch effect.

    I plan to use a Teensy for cap-sensing as they have hardware capacitive touch. However one Teensy can only do 10-11 so I will either need to use a mux or add more Teensies or find a capacitive touch device that can reasonably cover all 4 fingers for one side of the input device.

    There will, however, be a challenge here. Notice that the flex PCB is already resting over a finger, so there is a chance that the reading will already reflect that the electrode is being touched! I'll probably have to figure out how to make the circuit reject the finger stimulus it's already resting on and react only to thumb taps or touches!

    Before putting my ideas firmly down in a designed flex PCB for the same, I plan to use some copper foil and Kapton tape to make my own sense electrode. I've already ordered components for the same. Let's see how it goes!

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staticdet5 wrote 06/25/2019 at 15:39 point

I was really struck by your project, as I have frequently been in environments where I've wanted an input device, but haven't been able to carry or use a conventional keyboard.

I'm very reluctant to post, because I feel that feature creep is the bane of a starting project. But have you considered additional input locations  (you currently have 12 per hand). If you can get it to 20 per hand, you essentially have a full keyboard of 40 keys (36 alphanumerics, a space bar, enter, shift key, and a shift on the other hand).

Your idea is brilliant, and tremendously enabling for so many different use cases.  Best of luck!

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