I have a lot of questions about "chording keyboards"?   Ok, so what are they?... usually one handed devices for entering in alphanumeric information to an electronic device using one hand. Why "chording?... this is the system used to get many characters from only a few switches. The first use of this process that I recall was learning Morse Code. I remember trying to build a translator for code being received on the 40 meter band. I built a mechanical device that would stair step through a chart and translate the incoming code to  a character. I used a single pushbutton switch to enter the dots and dashes. While doing the sketches of the layout I stumbled onto the concept of using an "Array" for switches to encode characters. I have since designed hardware and software for over a hundred devices that included a keyboard matrix. 

The difference between a regular keyboard matrix and a chording keyboard layout is the the number of possible keys pressed. In most microcontroller circuits you will find only two possible lines are crossed in any given valid key press. In a chording keyboard you may press anywhere from one to five or even seven* switches.

*Seven switches seems to be a common factor in many designs. There are a lot of designs that use 3 switches for thumb and the four finger switches. Since 4 switches give 15 possible combinations and 3 thumb positions give a total possible 3 X 15 = 45 characters total.This is more than enough for alpha + numeric + function keys. Seven switches would be a Septambic keyer

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                            Names for various numbers of switches

	uni-ambic: one pushbutton switch or key;    also referred to as Iambic
	bi-ambic: two pushbutton switches or keys;
	tri-ambic: three pushbutton switches or keys; ...
	pent-ambic: five pushbutton switches or keys; ...
	sept-ambic: seven pushbutton switches or keys; ...  This is commonly used word
	multi-ambic: many pushbutton switches or keys;

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A way to validate the words in the list above is by
the number of GOOGLE hits per word searched

	uniambic                397 hits
	iambic             171,000 hits          3,420 hits for "iambic + keyer"  (Ham Radio)
	biambic                      1 hit           probably not a word
	diambic                  312 hits
	triambic                 254 hits
	pentambic                  9 hits          probably not a word
	septambic              100 hits
	multiambic               44 hits        all Google hits are for keyer's

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Uniambic                        http://electronicsusa.com/mk.html       1 switch Key for Ham Radio and Morse
                                                         By definition Ham's Iambic keyer's have 2 switches - dot/dash.

Pentambic                  http://www.bellaire.demon.co.uk/codes.htm    5 Switches chording example

Septambic                  http://www.cs.vassar.edu/~priestdo/chordhack/      7 Switches
                                                                        This is the best home built design I have seen.

                                   http://wearcam.org/septambic/    This is one you build from scratch.
                                                                                         Best looking ergonomic design

Multiambic                ? Many Switches

http://www.datahand.com/    two separate keyers one for each hand

http://www.handykey.com/  makers of Twiddler and now twiddler2
                  Review at  http://www.cc.gatech.edu/gvu/reports/2003/abstracts/03-37.html

http://www.thumbscript.com/howitworks.html   9 switch developed for cell phones

http://www.comp.utas.edu.au/users/nholmes/prfsn/tp2Jl.htm  8 switch based on ASCII

http://wetpc.com.au/html/technology/ruggedised.htm#kordpad  5 switch - Marine use
This is an example of an application that uses graphics on screen to tell you which fingers to chord with. This may be a way to build a trainer???

http://www.infogrip.com/product_view.asp?RecordNumber=12      7 switch desktop

http://www.chordite.com/        Interesting  Another Patent :-)

http://cuddlepuddle.org/~adam/pickey/index.html  PIC based 

http://www.4starelectronics.com/  Source of Obsolete IC's

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