Gameboy

Handheld Game Console — STM32F103

A battery-powered handheld game console built around an STM32F103C8T6. This repository holds the KiCad hardware design: a 2-layer board with an SPI TFT display, microSD storage, PWM buzzer audio, a six-button game pad, USB-C charging with automatic battery/USB power switching, and an SWD debug header.

Hardware at a glance

Schematic

The sheet is split into a power section (charging, power path, regulation and battery sensing) and a microcontroller section (clock, buttons, audio, display, microSD, USB-C and SWD).

Peripheral configuration

Peripherals and the clock tree are configured in STM32CubeIDE.

SPI1 drives the display, SPI2 the microSD card, TIM4_CH1 generates the buzzer PWM on PB6, and ADC1_IN6 reads the battery divider on PA6. The D-pad and A/B buttons are plain GPIO inputs, PD0/PD1 carry the external crystal, and PA13/PA14 are reserved for SWD.

Design notes

Power tree

USB-C VBUS ─┬─ MCP73831 charger ── +BATT ── JST-PH battery
            │        (R9 = 2k → ~500 mA charge current, status LED)
            │
            ├─ D3 Schottky ─────────┐
            │                       ├─ V_SYS_IN ─ SW10 ─ AMS1117-3.3 ─ +3.3V
+BATT ── Q2 AO3401A P-MOSFET ───────┘
         (gate tied to VBUS, 100k pulldown)

With USB plugged in, VBUS pulls the P-MOSFET gate high and disconnects the battery from the system rail, so the load runs from USB while the charger works on the cell. Unplug USB and the 100 kΩ pulldown turns the MOSFET on, handing the system back to the battery. The Schottky keeps battery current out of VBUS.

The 3.3 V analog supply is filtered from the digital rail through a 120 Ω ferrite bead with 10 nF + 1 µF, and each VDD/VBAT pin gets its own 100 nF capacitor alongside a 10 µF bulk cap.

Battery monitoring

A 100 kΩ / 100 kΩ divider halves the battery voltage into PA6 (ADC12_IN6), so a full 4.2 V cell reads about 2.1 V — comfortably inside the ADC range.

Buttons

All six game buttons switch to ground, so the firmware enables the internal pull-ups. SW9 selects the BOOT0 level through a 10 kΩ resistor for the bootloader, and SW10 is the main power slide switch ahead of the regulator.

Audio

PB6 (TIM4_CH1) drives the base of a BC847 through a 1 kΩ resistor; the buzzer sits between +BATT and the collector with a 1N4148W flyback diode across it. Tone generation is therefore a straight PWM/timer job in firmware.

STM32F103C8T6 pin map

The USB D+ line carries the 1.5 kΩ pull-up to 3.3 V required for full-speed device enumeration. The display backlight pin is tied to 3.3 V through a 10 Ω series resistor.

Connector pinouts

J1 — display (1×8, 2.54 mm)

J5 — microSD (1×4, 2.54 mm)

J2 — SWD (1×4, 2.54 mm)

Bill of materials

57 placements, all SMD except the headers, switches and buzzer.

Repository layout

Gameboy.kicad_pro     KiCad project
Gameboy.kicad_sch     Schematic (single sheet)
Gameboy.kicad_pcb     Board layout
MyParts.pretty/       Custom footprint library
docs/                 Schematic print and STM32CubeIDE configuration images

Opening the project

Install KiCad 6.0 or newer, then open Gameboy.kicad_pro. Newer KiCad versions will offer to upgrade the file format; the custom footprint library MyParts.pretty is referenced from the project and needs no extra setup.

Author

Talha Khan