Pomodoro Cube

Overview

The Pomodoro Cube is a handheld productivity device engineered to fit entirely within the dimensions of a standard Rubik’s Cube. Rather than relying on a touchscreen or physical buttons for its primary interface, the device uses orientation as its main input: rotating the cube selects, starts, pauses, and resets a Pomodoro session. When placed on its custom magnetic charging dock, the device transitions into an expanded mode that adds a digital clock, a Tamagotchi-style virtual pet, and a running log of focus statistics.

Every subsystem — the CAD-designed cube enclosure and charging dock, the custom KiCad PCB, the analog signal circuitry, and the CircuitPython firmware — was designed under the constraint of fitting within those dimensions, which shaped nearly every hardware decision on the project.

Highlights

• CAD-designed enclosure and dock: modeled the cube’s shell and its magnetic charging dock from scratch in CAD, iterating the internal layout until the battery, PCB, display, and sensors all fit within the target dimensions.
• Zero-button standalone mode: orientation sensing via an onboard MPU6050 drives timer selection and countdown, paired with a real-time clock and live battery/temperature readout, so the device runs entirely without physical buttons.
• Analog button multiplexing: the magnetic dock interface exposes only four physical contacts (5V, GND, 3.3V, Data), which ruled out dedicating a separate GPIO pin to each of the four dock buttons. I designed a resistor-ladder network that maps each button to a distinct voltage threshold, allowing all four to be read reliably from a single analog input.
• Safe battery monitoring: a hardware voltage divider steps the LiPo battery’s 4.2V peak down to a level safe for the ESP32’s ADC, letting the firmware calculate remaining battery percentage without risking damage to the microcontroller.
• State-machine firmware architecture: the CircuitPython firmware is structured as a memory-efficient finite state machine that cleanly separates standalone logic (clock/timer) from docked logic (Tamagotchi/stats), preventing memory fragmentation and keeping sprite animations smooth.

Future Improvements

Although the current prototype is fully functional, there are several improvements I would like to explore.

• Custom PCB for the charging dock to replace the perfboard prototype
• Improved magnetic charging reliability
• Lower-power sleep mode
• Configurable timer durations
• Improved charging dock alignment
• Historical productivity graphs
• Rotating screen animation to make the interface fixed

What I Learned

• Soldering fine-pitch components: hand-soldering small capacitors and resistors taught me the precision needed for clean, reliable connections at this scale.
• Custom PCB design: took the cube’s mainboard from schematic through a fully routed layout in KiCad, working within the tight space constraints of the enclosure.
• Constraint-driven engineering: fitting an entire product within the dimensions of a Rubik’s Cube forced better decisions everywhere else, from analog signal multiplexing to memory-conscious firmware design.

Demonstrations

Gallery