LM20MeshNode

Pocket Meshtastic node built around the Nordic nRF54LM20A (Minew ME54BS13 module), with an Ebyte E22-900MM22S (SX1262) LoRa module, an Ebyte E108-GN04S GNSS receiver and a Nordic nPM1300 PMIC for a single-cell LiPo battery. It connects to the phone over Bluetooth LE.

Features

MCU: Minew ME54BS13 (nRF54LM20A, Bluetooth LE with integrated antenna), USB-C to the nRF54LM20A USB port, 2×5 1.27 mm Cortex Debug (SWD) header (J201) and debug UART pads.

LoRa: Ebyte E22-900MM22S (SX1262, up to 22 dBm) with U.FL antenna connector (J301). TXEN is driven by DIO2 on the board; RXEN comes from the MCU.

GNSS: Ebyte E108-GN04S with U.FL antenna connector (J401). Fit L401 (82 nH) to power an active antenna. The GNSS supply (nPM1300 BUCK1) is off at power-up and is switched by firmware; the backup supply (V_BCKP) stays on from 3.3 V.

Power: nPM1300 PMIC with USB-C input and ESD protection, 1S LiPo charger (JST PH 2.0, J102), on-board 10 kΩ NTC, 3.3 V main rail (BUCK2), power button (SW101) on SHPHLD, charge and error LEDs, and a battery voltage divider to an ADC input.

User interface: 0.91" 128×32 OLED (SSD1306) on the back, three side buttons (UP, OK, DOWN), magnetic buzzer and a status LED.

Sensors: Nyfea SHT41-P-NF temperature/humidity sensor (SHT41 compatible), thermally isolated by a slot, and an ST LSM6DS3TR-C IMU wired for wake-on-motion (INT1 on P0.02).

Expansion: 4-pin 1 mm I²C connector (J501, Qwiic-style pinout: GND, 3.3 V, SDA, SCL).

Board: 4 layers (signal / GND / 3.3 V / signal), 40 × 85.68 mm, 1.6 mm, M2 mounting holes. All SMD parts are on the top side.

nRF54LM20A pin map

FunctionPinNotesLoRa SPI (SPIM22): SCK, MOSI, MISO, NSSP1.17, P1.16, P1.15, P1.18LoRa BUSY, DIO1, NRSTP1.19, P1.23, P1.26LoRa RXENP1.13TXEN from DIO2; optional MCU TXEN on P1.12 (R302, not fitted)I²C (TWIM30): SDA, SCLP0.03, P0.044.7 kΩ pull-upsGNSS UART (UARTE20): MCU TX → GNSS RXD, GNSS TXD → MCU RXP1.03, P1.291 kΩ series resistorsGNSS PPS, resetP1.04, P1.00GNSS power enableP1.05To nPM1300 GPIO0PMIC interruptP1.06From nPM1300 GPIO1Battery voltage (divider 2 × 1 MΩ)P1.30 (AIN2)Buttons UP, OK, DOWNP1.27, P1.28, P1.25Buzzer (PWM)P1.09Status LEDP2.00IMU INT1, INT2P0.02, P0.05P0 can wake the chip from System OFFDebug UART (UARTE00): TX, RXP2.02, P2.07Test pads

I²C devices: nPM1300 0x6B, LSM6DS3TR-C 0x6A, SHT41 0x44, OLED 0x3C.

Firmware notes

The nPM1300 starts with the battery charger disabled. Firmware must enable charging over I²C. The board is designed so that LoRa and Bluetooth work without a PMIC driver.

The E22-900MM22S used here has a crystal, not a TCXO: do not define a DIO3 TCXO voltage.

The GNSS rail (BUCK1) must be set to 3.3 V and enabled by firmware.