A fully custom, open-source smart power bank, designed from scratch.
4S3P Li-Ion pack · bidirectional USB-PD · bench-supply output · TFT telemetry UI
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| Enclosure (prototype 3, lid off) | Live telemetry UI |
Warning
Work in progress: the design is not yet validated. This project involves Li-Ion batteries, which can overheat, catch fire, or explode if mishandled. Take any information here at your own risk and read the safety note below.
- 115 Wh: 12× 18650 cells (Sony Murata VTC5, 4S3P), 14.4 V nominal / 16.8 V max
- 2× USB-C PD: primary port is bidirectional (charges the pack and powers loads)
- 2× USB-A: fixed 5 V, individually switchable, current-monitored
- Lab output: banana-jack rail that behaves like a bench power supply
- Hardware-autonomous BMS: BQ77915 protection works even if all firmware fails
- STM32F401 supervisor: power-state FSM, charge management, TFT + rotary-encoder UI
- On-device gauge calibration: guided 9-step wizard on the display; a multimeter is the only tool needed (no bqStudio / EV2400)
- Develop without hardware: full-PCB emulator, desktop UI simulator, host-side unit tests
- I assume no liability for any damage to property, people, or components resulting from the construction or use of this project.
- Always double-check polarity before connecting the batteries.
- Do not attempt to assemble this circuit if you are not experienced in handling lithium batteries.
Hardware
- Assembled mainboard + Sensing-Board (
PCB/) - 12× 18650 Li-Ion cells, 4S3P (e.g. Sony/Murata VTC5)
- ST-Link V2 (or compatible SWD probe) to flash the STM32F401RBT6
- A USB-PD charger for the primary port, plus USB-C/USB-A cables to exercise the outputs
Software
arm-none-eabi-gcc: the firmware builds via the CubeMX-generatedMakefileinfirmware/cubeMX/, no IDE requiredst-flash(stlink-tools) or STM32CubeProgrammer, to flash over SWDgcc+SDL2: only needed forfirmware/emulator/andfirmware/interface-tester/(no hardware required to run these)- Optional: STM32CubeIDE / STM32CubeMX, only to regenerate peripheral init code from
cubeMX.ioc
Distributed design: cell safety, power conversion, PD negotiation and gauging
each live in a dedicated IC; the STM32 supervises, aggregates telemetry and
drives the UI. Block diagram in PCB/README.md.
Full IC breakdown (10 subsystems)
| Subsystem | Part | Role |
|---|---|---|
| Safety / Protection | TI BQ77915 + N-ch MOSFETs | Autonomous, software-independent cell OV/UV/SC/OC cutoff (4S, always-on) |
| Charger | TI BQ25713 | Buck-boost NVDC battery charger (driven by the TPS25750 on a private I²C bus) |
| Main USB-C PD | TI TPS25750 | Primary PD port controller; patch bundle streamed by the MCU at every boot |
| Aux USB-C PD | Infineon CYPD3175 (CCG3PA) | Secondary PD port negotiation (replaced the EOL STUSB4710) |
| Aux programmable rail | ST STPD01 | I²C-programmable supply for the secondary USB-C / lab output |
| Fuel gauge | TI BQ34Z100-R2 | Impedance Track™ State-of-Charge / Time-to-Empty |
| Telemetry | TI INA3221 | 3-channel voltage/current monitoring |
| Step-down | TI TPS54302 / TPS54202 | Auxiliary rails |
| ESD / I²C isolation | USBLC6, ISO1540 | Port ESD protection, isolated I²C to the battery-referenced gauge |
| Host | STM32F401RBT6 | I²C master, power-state FSM, thermal manager, HMI / supervisor |
| Path | Contents |
|---|---|
PCB/ |
KiCad projects: main board + cell sensing board |
firmware/ |
STM32 firmware, PD controller configs, emulator, UI simulator, tests |
docs/ |
Documentation, start here |
powerbank_enclosure/ |
3D-printable enclosure (F3D, STEP, STL, renders) |
Full tree
Ducker-Charger/
├── PCB/
│ ├── Ducker-Charger/ # Main charger board (schematics, layout, datasheets)
│ └── Sensing-Board/ # Cell sensing board
├── firmware/
│ ├── cubeMX/ # STM32F401 firmware (FSM, charge mgmt, UI, drivers)
│ ├── TPS25750/ # Primary PD controller config (JSON project + .bin)
│ ├── CYPD3175/ # Secondary PD controller firmware (hex, patches, LED driver)
│ ├── emulator/ # Full-PCB emulator: real firmware vs IC models (SDL)
│ ├── interface-tester/ # Desktop UI simulator (SDL)
│ └── tests/ # Host-side unit tests (FSM, charge, HPI, math)
├── powerbank_enclosure/ # 3D-printable enclosure (F3D, STEP, STL, renders)
└── docs/
├── hardware/ # Power architecture, pin map / BSP reference
├── firmware/ # Architecture, FSM, charge mgmt, boot, UI
└── assets/ # UI demo gif
Start from docs/README.md: full system overview and a
walkthrough of how the firmware works, with links to:
- Hardware architecture · pin-level BSP reference
- Firmware architecture · power-state FSM · charge management
- Boot & IC provisioning · gauge calibration wizard · UI / display reference
- KiCad projects & block diagram
Boots to MAIN (battery %, voltage/current, live current graph). Rotate the encoder to cycle MAIN → DETAILS → GRAPH → PORTS → STATS; press to open SETTINGS (per-port toggles, Lab output voltage/current, USB-C2 output ceiling, lock-all, brightness/auto-sleep, gauge calibration wizard, shutdown). A long press (or SETTINGS → Shutdown) puts the device into deep sleep; a short press wakes it back up if a charger is attached. Fault conditions open a dedicated FAULT screen automatically, naming the cause.
Full screen-by-screen reference: docs/firmware/UI_and_Display.md.
- 📊 Slides: Google Slides
- 🎬 YouTube walkthrough: youtu.be/msm0JCK7GhI
The project is split by layer, one owner per layer end-to-end (design, implementation, docs, tests):
| Member | Layer owned |
|---|---|
| Angelo Perotti | Hardware (PCB/KiCad), CubeMX project bring-up, boot & IC provisioning |
| Francesco Brunelli | Charge management: sensors, actuators, fault detection |
| Michelangelo Calia | Power-state FSM & fault handling |
| Maya | Display/UI stack: driver, widgets, screens, navigation |
Issues, suggestions, and pull requests are momentarily suspended, as this is a university course project.
Released under the Creative Commons Attribution-NonCommercial 4.0 Internationalç License (CC BY-NC 4.0). © 2026 Angelo Perotti.
You are free to use, modify, and build upon this work for non-commercial purposes, as long as you credit the author. See NOTICE for attribution details.