openwrite

DIY alternative to https://getfreewrite.com/ because I love the concept and the execution and can't justify the price.

Requirements

• write text files
• manage (switch between, copy, delete) multiple text files
• store N kB of text files
• sync text files with Google Drive folder
• 4 hours of active typing time
• rechargeable
• mechanical keyboard
• able to see last N typed words
• able to see system state (turned on, current file, etc)
• NOT able to do my typical time wasters (email, reddit, twitter) in an enjoyable way
• cheap, given the above constraints

Outline

• terminal-only linux
• raspberry pi zero W
• Raspbian Lite
• tiniest screen that's still legible
• rechargeable battery
• single PCB mount

Notes

decisions

• software: QMK, KiCAD, OpenSCAD
• switches: Nuphy Wisteria / Gateron KS-33
• computer: Raspberry Pi Zero W v1.1
• microcontroller for keyboard control: Adafruit KB2040 (https://github.com/adafruit/Adafruit-KB2040-PCB, https://github.com/drewgates/kb2040-kicad)
• keycap dimensions and gap: 19mm between lead centers (cap standard is ~18mm)
• power management: Adafruit PowerBoost 1000C (overkill, but I already own it)
• key layout: in flux, but 5x14 ortholinear to match Moonlander to start
• display: Waveshare 2" display ($15, https://www.waveshare.com/2inch-lcd-module.htm)

iterations

• charge/boost/buck functionality directly on the board (replace the Powerboost 1000C)
• Keyboard microcontroller directly on the board (replace the KB2040)
• integrated touchpad (https://www.cirque.com/glidepoint-circle-trackpads)
• microcontroller-powered text editor (move closer to alphasmart)
• RPiZ supports HDMI output / hot-swap boot micro-SD with regular RaspbianOS (move closer to a portable work station)
  • unclear if feasible: integrate usb-c hub so RPiZ can interface with my existing desk setup
• E-ink screen
• Add USB switching logic so switching the keyboard output doesn't require reseting the device (e.g. TS3USB221A, USB mux/demux that supports 2 upstream devices and one downstream device)
• Hotswap sockets (Mill-Max 3305-0-15-80)

reference projects

• through-hole pcb-mounted-microcontroller usb-c keyboard (discipline): https://github.com/coseyfannitutti/discipline
• through-hole pcb-mounted-microcontroller usb-c keyboard (framework): https://github.com/stevennguyen/framework
• mini computer with custom keyboard (penkesu): https://github.com/penk/penkesu
• system76 launch keyboard with integrated USB hub: https://github.com/system76/launch
• Env-KB, a Raspberry Pi Pico keyboard: https://github.com/Envious-Data/Env-KB
• cyberdetox rpi400 mod: https://www.reddit.com/r/cyberDeck/comments/11tzifa/new_cyberdetox_displat_for_raspberry_pi_400/
• GreatScott DIY charge/boost: https://www.youtube.com/watch?v=Fj0XuYiE7HU, https://www.instructables.com/DIY-LiPo-ChargeProtect5V-Boost-Circuit/

kicad

• intro to kicad by hymel/digikey: https://www.youtube.com/playlist?list=PL3bNyZYHcRSUhUXUt51W6nKvxx2ORvUQB
• getting to blink 5.0 by conceptual electronics: https://www.youtube.com/playlist?list=PLy2022BX6EspFAKBCgRuEuzapuz_4aJCn
• schematic simulation / SPICE integration: https://www.kicad.org/discover/spice/
• visually interesting circuit simulator with lots of examples: https://www.falstad.com/circuit/circuitjs.html
• https://blog.oshpark.com/2020/10/08/kicad-3d-viewer-can-now-render-after-dark/
• https://github.com/sethhillbrand/kicad_templates - includes OSH Park 2 layer (apparently validated by their team!)

random

• "A simple guide to electronics components" - https://www.youtube.com/watch?v=6Maq5IyHSuc
• https://datasheets.raspberrypi.com/rp2040/hardware-design-with-rp2040.pdf
• microcontroller socketing: https://docs.splitkb.com/hc/en-us/articles/360011263059-How-do-I-socket-a-microcontroller-
• https://www.youtube.com/watch?v=ezk02GJ9iMs
• https://ergogen.cache.works/
• https://wiki.ai03.com/books/pcb-design/page/pcb-guide-part-1---preparations
• https://learn.adafruit.com/pigrrl-zero - guide to create a Pi Zero powered gaming device, includes step-by-step on connecting battery and display.
• http://i.imgur.com/ZQHDGTV.jpg
• https://sudomod.com/forum/viewtopic.php?t=2666
• https://cdn.sparkfun.com/assets/learn_tutorials/6/7/6/PiZero_1.pdf
• https://www.neverstopbuilding.com/blog/wiring-micro-usb-pinout
• https://en.wikipedia.org/wiki/USB
• https://desertbot.io/blog/headless-pi-zero-w-wifi-setup-windows
• OpenSCAD libraries/models:
  • https://github.com/revarbat/BOSL
  • https://www.thingiverse.com/thing:1638529
  • https://www.thingiverse.com/thing:2186550
• Part dimension sources
  • https://learn.adafruit.com/adafruit-2-2-pitft-hat-320-240-primary-display-for-raspberry-pi/downloads
  • https://learn.adafruit.com/adafruit-powerboost-1000c-load-share-usb-charge-boost/downloads
  • https://www.raspberrypi.org/documentation/hardware/raspberrypi/mechanical/rpi_MECH_Zero_1p3.pdf