Tip: Shifted Inputs on Keyboard Hack

[Hornpipe2]

Problem:  I am designing a bartop running VAntAGE on old hardware.  Since I am limiting my CP to just a handful of inputs and parts on hand, I want to use a keyboard hack.  I'd like a Shift key to access admin functions, plus a joystick and three inputs (Fire 1/Fire 2/Coin).  VAntAGE does not support "combined" inputs as Mame does (e.g. you can't set "exit game" as "keyX and keyY at the same time"), so I need a clever way to create a hardware shift key.

Solution:  First, check out Tiger-Heli's guide to keyboard hacks here: http://www.mameworld.net/emuadvice/keyhack2.html

The idea is that the three buttons are rigged to a common "column" input in our matrix, and the "shift" key swaps them to a new column.  As an example, check out Appendix A on the site.  If we map the three buttons to keys D/S/A, and then wire their Column to the Shift button, we could rig Shift to switch column 21 over to 23 and instead cause key inputs of C/X/Z while it is held down.

A quick diagram to show what's happening is attached.  Basically, rig your three input buttons through the Common (center) connector to the three different (row) inputs on your encoder board.  Connect all three NO outputs to the Common on your Shift button.  Then connect the NC to your unshifted (column) input on the encoder, and the NO to your shifted (column) input.

Hope that makes sense.  It's not too complicated in action - just another idea for the mental toolbox.

[ghettodish]

I believe I-Pac has a built-in shift key to add secondary commands to all inputs. P1 start button

...but that's one heck of a work-around for a keyboard hack!

[Hornpipe2]

Yeah, dedicated key encoders offer all that (shift on I-Pac, Shazaaaaaaaaaaaaaaaaaaaaaaaaaaam! on Keywiz) - but for my very limited application needing only a joystick and three buttons, the keyboard hack is the easiest and cheapest way to solve my problems.