Paddle is a design experiment in a chorded keyboard using only two keys. The goal for it is to have an accessible and time-insenstive input system. A user that could operate only a single switch at time should still be able to use paddle to input data.
Radio operators can encode data using a single key by using the relative length between keying to distinguish between dits and dahs. To make an input system that is not based on time a second key is added. Starting from the state of (0,0) and finishing at the same state the series of key transitions can be used to encode input.
As paddle should be usable by toggling only one key at a given moment the following is a table of the allowed state transions using two keys.
(0,0) -> (0,1)
(0,0) -> (1,0)
(1,0) -> (0,0)
(1,0) -> (1,1)
(0,1) -> (1,1)
(0,1) -> (0,0)
(1,1) -> (0,1)
(1,1) -> (1,0)
The following state transitions are not allowed and must be rejected by paddle.
(0,0) -> (1,1)
(0,1) -> (1,0)
(1,0) -> (0,1)
(1,1) -> (0,0)
A paddle sequence consists of the following four operations - "A Down", "A Up", "B Down", "B Up" where "A" and "B" are the two keys. They can be shortened to "a", "A", "b" and "B".