As the single binary input, we selected the right mouse button. This allowed a variety of buttons to easily be connected to eLocutor. By opening up the mouse and soldering the desired button in parallel with the right mouse button, any electrician or hobbyist should be able to make the connection.
Figure 30-2 shows how we made a temporary connection for Professor Hawking's special switch: the circuit board at the left bottom is taken from the inside of a mouse, and the points at which the external switch was soldered are the ones where the right mouse button is connected.
Figure 30-2. Connecting Professor Hawking's switch in parallel to the right mouse button
If you can provide the software only a single binary input, one part of the graphic user interface is obvious: all choices have to be presented turn by turn in the form of a binary tree. At each node, if the user clicks within a fixed time, the interface selects it, which might open up further choices in the form of a subtree. If the user does not click, the software automatically takes him to the next sibling of the node and waits again for a click.
To implement this tree, we used the Visual Basic TreeView control. This should be looked upon as a tree that grows from left to right. If, at any node, you click within a user-selected time interval—which is set using a Timer control—you expand the node and ...