But I quickly realized that that your way is super easy to implement. Also, depending on the pin interface to the pad, my way may not have worked–does the pad even have a single pin none/any button pressed indicator?

3 pins indicate that a button is pressed in one of the three columns. 4 pins indicate that a button is pressed in one of the four rows. 3 4 = 7. Duh. (Head smack).

An extra benefit to this method is that, if you want, you can process multiple simultaneous key presses. The first method doesn’t do that.

How do you get the receipt online? I’m assuming that you have a script running on the computer that reads from the board’s USB interface and publishes on a quick and dirty PHP or Rails website. I don’t think the board could hold enough C code to call HTTP requests straight from the USB port (like IronKey does).

Anyway, this was my thought process as a computer programmer looking at your picture. Arduino looks soooooo fun! It was hardware that got me into programming anyway (LEGO Mindstorms robots). I can’t wait to buy a board.

The Digital Paperless Receipt System Will Make Your Life Easy!