Septabmic Chording Keyer

Inspired by Greg Priest-Dorman's Chorder wiki, I'm building a handheld chorded keyboard based on Spaceman Spiff's Chording Keyboard Experiment (SpiffChorder) with some earlier influence from Steve Mann's septambic keyer. Photos and designs published in this section are licensed under the terms of the GPL (3.0), same as the SpiffChorder project itself (since they could be considered derivative works).

I picked up a USBtinyISP AVR Programmer Kit, Barebones AVR dev. board and 28-pin ZIF socket from Adafruit Industries on the theory that it would be easier to preprogram the Atmega168 on a dedicated target board. Unfortunately, I followed the SpiffChorder instructions slightly out of order and burned the external clocking fuse before writing the firmware, thus rendering the unclocked devboard useless... so instead I programmed the microcontroller in-circuit later once the 12MHz crystal and associated components were in place to clock it correctly.

I started on a solderless breadboard, shown below, but those really aren't suited for higher-frequency prototyping and so I was getting stray USB device resets at random (particularly if I inadvertently brushed the ground line while not grounding myself first). I used the components in GPD's Digikey bill of materials, going with the 8x pull-up resistor SIP array since I was only testing with 7 keys. I also chose poorly on a preformed bank of 3 yellow LEDs which were somewhat larger than I expected and the leads weren't quite a multiple of 0.1" standard breadboard pitch. I used Adafruit's excellent AVR ATmegaXX8 Pinout Stickers to more easily keep track of what I was connecting.

I hacked up an old telephone handset from my junk pile so I could have something vaguely ergonomic into which to mount the keys. Once I'd separated the front and back of the handset, I opened up tracks for the keys using a small cutting wheel on a Dremmel. Epoxy was added in a few places and sanded to get the tolerances just right. I ordered some blank row-2 1x1 ABS plattic keycaps from WASD Keyboards and popped them onto the Cherry MX stems.

In an effort no to limit my capabilities with the keyer's software, I wanted to make sure whatever prototype I eventually built could double as a development board. To that end, I implemented all optional components of the SpiffChorder circuit (programming header, LEDs, pull-up resistors and screw terminals for all 8 chord keys and 3 modifier keys). I tried to keep the layout as compact as possible while still working on single-sided pad-per-hole perfboard, using entirely right-angle traces so as not to make stray contact with corners of square pads. It fits in a 17x21-hole grid including a ground bus all the way around the perimeter. Here's a top-down view showing the logical supply, ground and signal paths colored for easy identification:

This is the front showing just silkscreen markings and jumpers, as well as the traces on the back (mirrored for easier visual reference):

I was going to try laying it out with Fritzing, but got sidetracked when I couldn't find a resistor array in its parts library. Instead I wound up just sketching the layout on graph paper and transferring it into Dia by hand. Here's the multi-layer original from which the above graphics were exported. The same pathing could be used for a custom double-sided PCB, which I'll probably get around to making at some point.

Monocular Headmount Display

As I begin work on a wearable display, I'll flesh out this section. Here are some interesting links for components I'm considering:

Single-Board Wearable Computer

Right now I just go everywhere with an Asus Eee PC netbook running Debian GNU/Linux, but intend to transition soon to a low-power single-board computer. Some links for reference:

Portable Power Supply and Charger

Portable power will also be critical:

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