An ESP32-C5 badge running Solana OS.

The brain is an Espressif ESP32-C5-WROOM module, the shielded can on the back of the board. Inside is an ESP32-C5 (silicon rev 1.2): a single-core 32-bit RISC-V CPU at 240 MHz, a 48 MHz crystal and 16 MB of flash.

There is no PSRAM enabled, so Wi-Fi and the LVGL graphics stack share internal SRAM. Solana OS is built around that budget: one app runs at a time and every app frees its memory when you leave it.

An ILI9341 TFT sits in a bracket on the front, driven in landscape at 320×240 over the SPI2 bus. Its flex cable passes through a slot to an FPC connector on the back. The panel is BGR and color-inverted, and the driver rotates it into place.

The UI is rendered with LVGL 9 through esp_lvgl_port. The backlight has its own GPIO, active high, with an external pull-down so it stays dark until firmware turns it on.

The front has a four-way D-pad (UP, DOWN, LEFT, RIGHT) and two action buttons, SELECT and CANCEL. All six sit on a TCA9534 I2C GPIO expander at address 0x20, which pulls an interrupt line low when any of them changes, so the firmware does not have to poll the bus.

On the back, BOOT is wired straight to GPIO 28 with an external pull-up and works as Home in Solana OS. RST resets the chip. All buttons are active low, and Solana OS maps them to logical keys in one place, so apps never read raw button bits.

Eight WS2812B addressable LEDs are chained on one GPIO: six across the top edge (silkscreen D3–D8) and two beside the screen on the right edge (D9, D10). They are driven with Espressif's led_strip component.

Full power is blinding and pulls too much current, so the firmware caps brightness at about 24/255. In the reference firmware each held button lights its own LED.

The microSD slot is on the back, on the same SPI2 bus as the display, with its own chip-select on GPIO 4. There is no card-detect pin.

Sharing a bus with a display is harder than it sounds. A freshly powered card starts in SD-native mode and reads MOSI as its command line, whatever the chip-select level. The stock firmware ran about 4 s of LCD tests first, so pixel data reached the card as SD commands. The fix: mount the card before the display starts.

The ESP32-C5 has dual-band Wi-Fi 6 (2.4 and 5 GHz), Bluetooth LE 5 and an IEEE 802.15.4 radio. Solana OS uses Wi-Fi and ESP-NOW and leaves Bluetooth out of the firmware to save RAM.

For wired access there is a USB-C port on the back. UART0 goes through a CH340C USB-serial bridge, which carries flashing and a serial console at 115200 baud with commands like help, info, sd, ls, cat and rgb.

A 3.7 V 1000 mAh LiPo pouch (523450) covers the lower half of the back and plugs into a JST connector. An OFF/ON slide switch on the left edge cuts power.

There is no dedicated fuel-gauge chip. The battery voltage goes through a 1:1 resistor divider into ADC1 on GPIO 1, and firmware doubles the reading. Solana OS shows the result as a percentage in the status bar, and the Hardware Debug app shows millivolts too.