Tuesday, October 12, 2021

PiPi Mherkin

The Micro Gherkin

The tiniest Pi Pico powered keypad. Both the switches and the Pi Pico are surface mounted, back to back.

The 30 switches were selected from the jlcpcb.com SMT parts inventory. I had 5 boards made and assembled. The BOM is only 3 parts; switches, Pi Pico and the 3 tool marks (registration holes). JLCPCB supplies and SMT assembled the switches.

When I placed the order the Pick and Place preview looked incorrect, but after the order was placed and reviewed the preview was corrected.

Four of the boards. Top, bare bottom, bottom with Pi Pico soldered on, and an assembled board with 4mm M2 spacers and screws.

The board is running PRK firmware. PRK is very easy to use. It mounts the board as a USB drive so you can directly edit the configuration file with a text editor, much like KMK firmware/CircuitPython. I used the prk_pipigherkin configuration. The only change needed was to the pin definitions

  [ 12, 13, 14 ],
  [ 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 ]

I had also made a top plate, but the switches are so short that they don't protrude at all and can't be pressed. Also, in 2 of the 5 boards the switches were not aligned well enough to fit the top over them.

LCSC.com has variations of this switch with different heights and weights, but JLCPCB only had the 2mm tall/250g version available for assembly.

This is too small (64x26mm) for a practical keyboard, but it makes a decent, very compact macropad. Assembled with 4mm spacers it is only 9mm thick.

Files on git.