Membrane Keypad

Update 7/12/24: Minor changes to the SCAD source. Added a 60-key model with a 12×12mm grid.

Update 7/4/24: Updated SCAD source to make customizing easier. Added a ridiculous credit card sized keypad with 60 buttons (requires 1/8" wide copper tape and probably isn't really practical as a functioning keypad). 

Update 7/4/24: Added an option for the alignment bumps in SCAD source.

These models can be used to create custom membrane keypads. I've included models for 10 different configurations (2x2, 2x3, 3x3, 3x4, 4x4, with and without 3mm mounting holes), plus the OpenSCAD source in case you need something more customized. 

Printing

No supports needed. Just print a base and the corresponding top. PLA seems to work fine.

Assembly

Cover the rows (on the base) and columns (on the underside of the top) with conductive material. The design accommodates either ¼" (6mm) conductive tape or a layer of conductive ink. I ended up using copper foil tape. The conductive ink I had didn't seem to work very well.

If you're using foil tape, try to lay it down as smooth as possible. You don't want any big wrinkles causing false key presses.

Snap the top onto the bottom.

Wire up the rows and columns. You've got several options here. The base has wire guides and through-holes which might work well for connecting to conductive ink. With foil, you can sandwich wires between top and bottom to make a solderless connection. Or you can do what I did here and leave a bit of foil tape hanging out the sides and solder wires directly to that.

Connect the wires to your favorite keypad matrix decoder or microcontroller. I'm using an Adafruit Trinket for this.

For the graphics, 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.

The microcontroller and code are essentially the same as this keypad but this model is much less bulky and considerably quieter.

I also added a 60-key keypad that uses a 12×12mm grid. Here's a quick prototype of a rechargeable wireless keyboard using this model, with a Bluetooth-enabled microcontroller, a LiPo battery stuck to the back and laser-printed graphics stuck on top.