Minimal Key Calculator

[Garth Wilson]

I designed a commercial product in the late 1980's that used a gray-code rotary switch and a pair of buttons, per the instructions given me. The knob worked similar to the old Dymo label makers where you'd turn the dial until you got to the character you wanted and then press it into the pastic label tape. Turn the gray-code switch and the choices would scroll through a character position in the LCD (including choices for backspace, exit, etc.), then press the "Enter" key. There was also a "Cancel" key, and pressing both together was "Help." Later I did it with only keys, an up-arrow, down-arrow, Enter/Yes/Continue, Cancel/No/Exit, and Help/Menu. A friend uses a piece of equipment at his work that uses the knob with a pushbutton behind it (so you can rotate and press the knob), so everything is in one control. The virtue, I suppose, is in not requiring so much panel area in situations where you don't spend much time operating it. The rotary switch is expensive though, and certainly takes more depth behind and in front of the panel. For something like the calculator, I don't think there's really a virtue in minimizing the key count.