Moonshine NRF52 Mini

Minimal DIY Meshtastic node variant: nRF52840 + RA-01S-P (SX1262) LoRa module with a single status LED on P0.13. No display, GPS, button, or battery ADC - LoRa-only minimal system.

Hardware

MCU: nRF52840 (512 KB flash / 128 KB RAM)
LF clock: external 32.768 kHz crystal (USE_LFXO)
LoRa: Ai-Thinker RA-01S-P (SX1262, no TCXO, internal RF switch, 22 dBm max)
- SX126X_MAX_POWER=22
- TCXO_OPTIONAL (no TCXO on module - firmware tries XTAL first)
- DIO2 drives TXEN internally; RXEN is controlled by P0.17
LED: status LED on P0.13 (active high, LED_STATE_ON = 1)

Pin map

Function	Pin	Notes
SPI_MISO	P0.02	LORA_MISO
LORA_RESET	P0.09	SX126X_RESET
LORA_DIO1	P0.10	SX126X_DIO1 (IRQ)
LED	P0.13	Status LED (active high)
LORA_RXEN	P0.17	SX126X_RXEN
LORA_BUSY	P0.29	SX126X_BUSY
SPI_SCK	P1.11	LORA_SCK
LORA_CS	P1.13	SX126X_CS
SPI_MOSI	P1.15	LORA_MOSI

Only the status LED on P0.13 is wired (no button, battery ADC, GPS, or display). The board has no user button, so DFU entry is via the 1200 bps touch or SWD.

Build & Flash

Build

pio run -e moonshine_NRF52_node_mini

Uses PRIVATE_HW (HardwareModel 255) - no protobuf or architecture.h changes required.

The build links against nrf52840_s140_v7.ld, so the application is linked to start at 0x27000 and requires the S140 SoftDevice v7.x to be present on the chip at 0x0-0x26FFF (or the Adafruit nRF52 UF2 "bright-future" bootloader, which bundles its own SoftDevice). The build output (firmware-*.hex / .uf2) contains only the application, not the SoftDevice.

Flash (first time on a bare nRF52840)

A factory-fresh nRF52840 has no SoftDevice and no bootloader. The SoftDevice must be flashed once via SWD before the application; otherwise Bluefruit.begin() fails, sd_flash_* calls (LittleFS, NodeDB, config persistence) return errors, and the node appears dead.

The S140 v7.3.0 SoftDevice hex is shipped in this repo at bin/s140_nrf52_7.3.0_softdevice.hex. Flash via SWD with OpenOCD (CMSIS-DAP / J-Link / ST-Link). The nrf52_recover command does a chip-wide ERASEALL through the nRF52 CTRL-AP and clears APPROTECT, so it is the recommended first step on a fresh module (ebyte/Raytac modules ship with APPROTECT engaged).

# Full flow: recover (erase all + unlock) -> SoftDevice -> app -> reset
C:/openocd/bin/openocd.exe -s C:/openocd/share/openocd/scripts \
  -f interface/cmsis-dap.cfg -f target/nrf52.cfg \
  -c "init; nrf52_recover; \
      program bin/s140_nrf52_7.3.0_softdevice.hex verify; \
      program .pio/build/moonshine_NRF52_node_mini/firmware-moonshine_NRF52_node_mini-*.hex verify; \
      reset run; exit"

Flash (app only, SoftDevice already present)

When the SoftDevice is already on the chip and only the application changed (e.g. after editing the variant and rebuilding), skip nrf52_recover and the SoftDevice line:

C:/openocd/bin/openocd.exe -s C:/openocd/share/openocd/scripts \
  -f interface/cmsis-dap.cfg -f target/nrf52.cfg \
  -c "init; \
      program .pio/build/moonshine_NRF52_node_mini/firmware-moonshine_NRF52_node_mini-*.hex verify; \
      reset run; exit"

Notes

The firmware hex filename contains a commit hash (e.g. 2.8.0.421838f); use the actual file produced by pio run or a shell glob.
The SoftDevice hex occupies 0x0-0x26498 (~156 KB) and does not write UICR, so nrf52_recover is safe (UICR resets to defaults).
Swap interface/cmsis-dap.cfg for interface/jlink.cfg or interface/stlink.cfg if using a different SWD probe.
No UF2 bootloader is installed in this flow, so subsequent updates must go through BLE DFU (secure DFU service) or SWD again. To enable UF2 drag-and-drop updates, flash an Adafruit nRF52 UF2 bootloader (https://github.com/adafruit/Adafruit_nRF52_Bootloader) at 0x0 in place of the bare SoftDevice - the bootloader bundles its own SoftDevice.

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