2015-10-03 (Sa) Wrist Mounted Chording Keyboard

Attention was turned from the wrist movement pieces to a sensor which could detect hand movement. Several devices were considered.

Plans were drawn for a system which would make a whisker switch from a roller switch. The premise was that the long lever, drawn in red, would rest comfortably on the back of the wearer's hand and when the wrist was extended backward it would close a switch. Additionally, since it worked on a cam at the fulcrum, the lever could extend much further without adding significant resistance so movement would not be impeded. This design also used a pivoting base so the angle where the switch would trigger could be fine tuned for each wearer. Drawbacks to this design were a complicated model and a large roller switch made for a large device.

Cam & roller switch design

Next design used the principle of the infrared proximity sensor but kept the emitter and detector separate. The emitter would be made as an LED ring with a battery and would simply be kept turned on all the time. When the user tilted the hand backward the ring would shine through a lens and activate an array of photodiodes. Using this design would give a range of inputs so it could act as multiple switches and perform multiple functions. A battery operated ring was unappealing.

Light emitting ring shining on an array of photodiodes

The last design was very similar to an infrared proximity sensor except it used tunnels for the emitter and receiver to narrow the region it would focus on. Hopefully this would allow the device to work in all kinds of lighting conditions by reflecting the beam of the emitter off the back of the hand. By reflecting rather than relying on a ring or whisker switch this makes it contactless.

Narrow-beam proximity detector

Downloadable Files:
To do:
  • Wrist mount
    • Servo arms
      • Bend around spacers
    • Terminal board
      • Input voltage
        • USB
    • Make base for keyboard
      • Spacers 
    • Integrate:
      • Enclosure for each controller
        • Potentiometer access
      • Activation switch
    • Debug 
    • Test
    • Refine
    • Repeat
  • Write instructions
    • Compress and link to all files
      • OpenSCAD files
      • STL models
      • Arduino code 
    • Make diagram with every part labeled 
    • Schematic for servo controller

The rest of the posts for this project have been arranged by date.

First time here?

Completed projects from year 1.
Completed projects from year 2

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2015-10-02 (F)