Building pair of pedals is easy. You'll need COM port mother jack (9 pin), a cable with at least
three wires and two buttons. I used two "tact buttons" SWT-9. Your buttons must connect
pins 7 and 8 (button 1) and pins 6 and 7 (button 2) (CTS and DSR from serial controller's point of view). It's better to make small bags from plastic for these buttons, to protect them from the dirt
on the floor.
Why two pedals? Because it's automatic key. When you push one of them
(or depress one... you can sit with both feet on pedals relaxed and just
raise left or right foot a little)
driver will sound dots and other pedal will give you dashes. It's much
easier than conventional key, where you have only one switch and you are
responsible for dot and dash lenght.
I'll try to shoot some photographs while making another pedal set, scan them and put here.