Steve DeGroof's Parametric Macropad Design Drops the Switches for a Clever 3D-Printed Membrane
A design of which Sir Clive Sinclair would be rightly proud, this low-profile macropad can be scaled to arbitrary matrix dimensions.
Maker Steve DeGroof has designed a professional-looking 3D-printable macropad that eschews mechanical switches in favor of a low-profile membrane design — with laser-printed top layer for added style points, and a parametric design that scales all the way up to a 60-key compact keyboard.
"A configurable membrane keypad," DeGroof explains of his creation, which was built to give rapid access to the his most commonly-used yet relatively inaccessible-on-a-standard-keyboard symbols including en dash, em dash, degree, superscript two, pi, and multiplication. "Low profile, low activation force."
Macropads are nothing new to makers, with a wide variety of designs available from single-key upwards — but DeGroof's stands out through the use of a custom membrane in place of the usual mechanical or tactile switches. The membrane is 3D-printed in two layers, and copper foil tape or conductive applied to both layers. The two layers then click together, with pressure on the hand-made contacts completing the circuit.
"For the graphics," DeGroof explains of the final upper layer, "you'll need a printed (laser or inkjet) sheet stuck to the top. I used vinyl sticker paper for this one but any paper label should suffice. Connect the wires to your favorite keypad matrix decoder or microcontroller. I'm using an Adafruit Trinket for this."
While DeGroof designed the printable keypad for quick access to unusual keys, he's also prototyped a larger yet still only credit card-sized variant that offers a Sinclair ZX80-style 60-key design to act as a compact alternative to a full-size keyboard. The housing of the ortholinear keyboard is big enough to hold a Bluetooth-enabled mcirocontroller and a lithium-polymer battery, making it suitable for cordless use.
Print-ready STL files for 10 different keypad sizes and parametric SCAD sources, which can deliver membranes of arbitrary dimensions, are available on Printables under the Creative Commons Attribution 4.0 International license. Additional information is available in DeGroof's Mastodon post.