A CR2032-powered keychain clock, minimalist, open hardware, and built to last.
Hydrogen V1 is a coin-cell (CR2032) powered keychain clock designed around aggressive power optimization and a minimal BOM. It wakes on button press, displays the time on an SSD1306 OLED for 5 seconds, then returns to deep sleep, targeting a ~6-month battery life on a single CR2032.
This is the first device in the Hydrogen line, part of the broader PhenixTech hardware project ecosystem.
CR2032
│
├──[BAT54 Schottky]──► VBAT
│ │
│ └── [22µF holdover cap]──► PCF8563T VBAT
│
├──► CH32V006 (TSSOP20)
│ │
│ ├── I²C ──► PCF8563T RTC
│ ├── I²C ──► SSD1306 OLED (daughter board)
│ ├── GPIO ──► LED (3kΩ, ~500uA, low-battery indicator)
│ └── SWIO/RST pads (debug header)
│
└──► 3215 32.768kHz crystal (RTC clock source)
| Component | Part | Package | Unit Cost |
|---|---|---|---|
| MCU | CH32V006F8P6 | TSSOP20 | €0.165 |
| RTC | PCF8563 | SOP8 | €0.155 |
| Crystal | 32.768kHz SMD | 3215 | €0.10 |
| Schottky | BAT54 | SOD-23 | €0.012 |
| LED | Red, 0603 | 0603 | €0.007 |
| Nav | 3-way thumbwheel | SMD | €0.057 |
| Total (timing/control) | ~€0.50 |
Display module (SSD1306 0.96" I²C) sourced separately. (about 0.50€ each)
- Two-PCB approach — main board + SSD1306 module daughter board with a 4 pin headers. V2 will integrate a bare OLED panel on a single PCB.
- BAT54 Schottky — keeps the RTC domain isolated for the holdover cap.
- 22µF holdover cap — keeps the RTC alive for ~20 seconds during a battery swap, preserving time (also allow a clean shutdown).
- Debug interface — three pads (SWIO, GND, RST) with a 2.54mm pitch for WCH-LinkE programming.
Developed with the WCH SDK / MounRiver Studio II
[Power on / button press]
│
▼
Wake from deep sleep
│
▼
Read time via I²C (PCF8563T)
│
▼
Display on SSD1306 (5 seconds)
│
│
│
▼
Return to deep sleep
| State | Current | Duration |
|---|---|---|
| Deep sleep (MCU + RTC) | 60uA | ~99% of time |
| Active (OLED on, MCU running) | 8mA | 5s per wake |
| LED flash (low-battery) | ~500uA | brief pulse |
Designed in EasyEDA, fabricated by JLCPCB, components sourced from Aliexpress.
- 2-layer PCB, 1.6mm thickness
- SMD components on top side; CR2032 holder on bottom
- Compact form factor for keychain use
- Two-board stack: main board + OLED module daughter board
A two or three-part enclosure is in design:
- Back shell — resin cast
- Front plate — plastic with OLED window and LED cutout
- Optional — magnetic swappable faceplate system
| Version | Status | Key Changes |
|---|---|---|
| V1 | ✅ | Two-board stack, SSD1306 module |
| V2 | 🔲 Planning | Single PCB, bare OLED via FPC, MOSFET power gating, reverse polarity protection, optimized layout |
Hydrogen is part of my own hardware ecosystem, where projects are named after elements and subatomic particles:
- Boron — main handheld line (RP2350, ST7789 display)