Kitsujikan

Kitsujikan

A rechargeable, pocket-sized Pomodoro timer with an OLED display and colour-coded buttons, designed for Hack Club's Half-Life 10-week hardware challenge.

Front	Back

Features

• One-press focus sessions: 30, 60 or 90 minutes, one button each.
• Automatic breaks: when a session ends, the buzzer sounds and the timer offers a 5-minute break. Press green to accept or red to skip. After the break, it offers to repeat the last session length.
• Clear display: a 0.96" OLED shows the time left as HH:MM:SS. Hours are hidden when zero, and minutes and seconds always show two digits.
• Pause: press red during a session.
• Battery powered: runs from a LiPo battery and charges over USB-C, with an on/off switch and battery-level sensing.
• Low power: sleeps when idle, and the 30/60/90 buttons wake it from deep sleep.

Status

• Schematic
• PCB layout and routing (DRC clean)
• Gerber and drill files
• Bill of materials (BOM)
• Order the PCB and parts
• Firmware: first version (untested on hardware)
• Assembly and testing
• Enclosure

Hardware

| Power | 3.7 V LiPo (JST-PH), slide switch, 2 × 200 kΩ battery-sense divider | | PCB | 2 layers, 65 × 90 mm, all through-hole parts |

Pin map

Directory structure

PCB/                 KiCad 10 project (schematic + board)
PCB/libs/            Symbol, footprint and 3D libraries used by the project
PCB/production/      Gerber and drill files for manufacturing
renders/             3D renders of the board
Firmware/            Arduino firmware for the XIAO ESP32-C3
kitsujikan_BOM.csv   Bill of materials with sources and estimated prices

Bill of materials

The full list with links is in kitsujikan_BOM.csv. Summary:

Prices in the CSV are rough estimates. Many Amazon items come in multi-packs, so the first build costs more than the parts on one board.

Ordering the PCB

1. Zip the contents of PCB/production/.
2. Upload the zip at jlcpcb.com.
3. The defaults work: 2 layers, 1.6 mm, HASL. Pick any solder mask colour.

Notes on assembly

• Mount the XIAO on female headers, not flat. The battery connects to pads on its underside (BAT+ / BAT−). Solder two short wires to those pads, thread them through the J2 holes, and solder them on the back.
• Check the OLED pin order before soldering its socket. This board expects GND, VCC, SCL, SDA.
• Check the LiPo plug polarity before plugging it in. J1 pin 1 is +. Battery plug colours aren't standardised.
• Charging only works with the power switch ON, because the switch disconnects the battery.
• Keep the battery away from the sharp solder joints on the back. Use foam tape, or standoffs and a back plate.
• Solder the low parts first (resistors, diode), then the transistor, buzzer, switches and headers.

Firmware

Arduino (C++) for the ESP32-C3, in Firmware/. It covers the timer state machine, debounced buttons (tap / hold), buzzer melodies, the OLED screens, battery percentage, and deep sleep with wake-on-button. Build steps and controls are in Firmware/README.md. The timer logic has laptop unit tests in Firmware/test/.

Acknowledgements

• Hack Club and the Half-Life challenge
• Starbie, the Half-Life Week 1 example project, and its care-package libraries
• Seeed Studio for the XIAO KiCad symbol library

License

This project is released under the MIT License. Third-party libraries in PCB/libs/ remain under their original authors' licenses.