2015-10-26 (M) Wrist Mounted Chording Keyboard

Proximity detector hardware was still malfunctioning yesterday. Reliable reads couldn’t be taken. The problem was assumed to be a matter of the infrared emitter broadcasting excessively strong. An adjustable resistor was added to the circuit to change the resistance for testing. There was already a 910Ω resistor in series with the emitter when a 10KΩ resistor was added. Some adjustments were made and it seemed to improve but there was no consistency.

Liquid tape had not been applied to the back of the sensor so to test the thought that it could have been a matter of light leaking out the back a small bit of cardboard was inserted between the emitter and receiver. Results were instantly visible. The testing program was intended to turn the RGB LED red when an obstacle was detected and blue the rest of the time. As soon as the cardboard was put between the emitter and detector the unreliable reads disappeared.

More testing was done with the adjustable resistor in place. When the emitter was turned down very low only a reflective surface could trigger the detector but the original resistor by itself provided very reliable results returning 94% of attempted reads. The threshold in the program was set to 90% to account for noise and mechanical differences of other people’s hardware.

Testing the light leakage with a piece of cardboard

Liquid tape applied to back of emitter-receiver tubes

Importance of blocking the light leaking was not apparent until these experiments. If a divider had been modeled into the design earlier some of this testing may have been unnecessary but the liquid tape does a suitable job. Testing was done after applying liquid tape and it was successful. Most recent code for the servo controller is available below.

To do:
  • Trim bolts on wrist mount (3)
  • Use locknuts on hinge points (2)
  • Insert screws into servo horns into servo (2)
  • Install longer spacers for hinge-side keyboard end 26.5mm long (2)
  • Velcro or magnets for attaching keyboard to holder
  • Add velcro to a battery pack
  • Write instructions 
    • Compress and link to all files
      • OpenSCAD files
      • STL models
      • Arduino code 
    • Name everything and use name uniformly throughout instructions 
    • 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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2015-10-26 (M)