Tactile Touchscreen Calculator Brings a Retro Feel to Modern Technology

At the 2020 HPCC Handheld Conference this past October, Michael Park presented his design for a touchscreen calculator that replicates the feel of the keys on classic units. Hardware today doesn’t quite feel like it used to, and for some, like Park, nostalgia is a powerful force in designing.

Beginning the design for the MP-29 Tactile Touchscreen, the big considerations were the CPU/software, the display, the case, and, importantly, the keys. Wanting actual keys instead of a single touchscreen, it became attractive to create keys with built-in displays. This would eliminate the need for printed legends and allow each key to dynamically indicate its current function. Existing components proved both too large and prohibitively expensive, necessitating a different approach and leading right back to touchscreens. Touchscreens offer all the benefits Park sought save one: they lack tactile feedback.

To configure his calculator to include that one elusive element, Park decided to test configurations where he mounted the touchscreen onto a tactile switch. After a few iterations, he ended with a device that you could press and feel the key travel, complete with a satisfying click at the end of its journey. In the final design, a single touchscreen rests above a switch that provides feedback with a scissor-arm guide mechanism, pictured above. A plate hooked onto the scissors keeps the touchscreen level, so the button underneath is activated no matter where you press.

With this factor solved, it became possible to create a calculator based on the HP-29C design with a fully reconfigurable pad of 30 keys, all with dynamically updateable labels. Two separate gold and blue shift key included reconfiguring the layout to show each key’s respective “shifted” function. With just the touchscreen, however, the keys could prove difficult to locate, so the casing includes a physical keyboard laid atop the touchscreen.

The experiment isn’t totally complete, and Park himself calls his design a stopgap until smaller, less expensive display switches become available. Still, it’s a rather clever solution to create a much-desired effect and looks satisfying to use. You can watch him talk through the process and demonstrate the mechanism in a video archived here. Future intended updates to the design include bug fixes, a stiffer scissor mechanism, possible alternative mechanisms, and more experimentation with the dynamic layout, which currently closely mimics the HP-29C.