“I have a coworker who is fond of reminiscing about the good ol’ days, when his grandparents had a rotary dial phone on the wall that they were renting from the phone company. Combine this with his devotion to the tenkey pad on a full-size keyboard and the fact that I happened to have an old rotary dial in my bin of spare parts, and the path forward for this year’s April Fool’s prank was self-evident.
I mean, of course, that buying a cheap $13 mechanical keyboard off eBay and hacking the rotary dial into it was the most reasonable course of action.
While the easy route out with a fabrication project like this is just to go for cosmetic completeness, I figured that it was imperative that the dial actually work for numeric input - especially since I was planning to remove the number row as well, thus forcing the use of the rotary dial for numeric or symbolic entry.
My rotary dial has two primary pairs of contacts. One goes open when the dial is moved past the 1 position, and the other creates the characteristic pulse train upon release (one pulse per numeric position). While one could use a pin-change interrupt, the timescale is so large that busy-waiting is acceptable. I used a DFRobot Beetle for this since its onboard ATMega32u4 provides native USB HID functionality.”