Matrices and Duplex Matrix
Improving upon their design.
Maximizing the matrix
For non-macropad keyboards, routing a matrix with one pin per row and column will almost always lead to inefficient results.
With the same number of keys, a more "square" matrix will require less cols and rows total than a more "rectangular" one.
I.E. For 30 keys, 5x6 is 11 pins, while 2x15 is 17 pins.
The Duplex Matrix
Each "column" spans two physical columns.
Two "rows" exist for each physical row.
See schematic at bottom for a routing example.
Pros
Fit more keys for rectangular keyboards using less pins
More pins to use for fancy features
Use cheaper controllers to reduce the final product cost
Cons
More complicated to wire
Can be more difficult to add more keys to the matrix later on
Harder to follow on a schematic