RoyalNode

RoyalNode / 2Watt Project

RoyalNode, also tracked as the 2Watt Project, is a solar-powered 915 MHz LoRa repeater carrier built around the Seeed Studio XIAO nRF52840 and EBYTE E22-900M33S high-power radio module.

Status: Rev A KiCad schematic and PCB placement scaffold are active. The board is not fabrication ready.

Locked architecture

• Standard Seeed Studio XIAO nRF52840, socketed
• EBYTE E22-900M33S radio module
• Protected 1S 3.6/3.7 V Li-ion/LiPo pack, 10-20 Ah class
• Board-mounted XT30 battery connector
• Board-mounted XT30 solar connector
• BQ25798 buck-boost charger with MPPT and power path
• Battery-mounted Semitec 103AT-2 NTC connected to BQ25798 TS network
• TPS61088 5 V boost rail for the E22
• Battery voltage and charger telemetry read directly from the BQ25798
• XIAO powered through its underside BAT and GND pads using a two-wire JST-GH lead
• LM66100 ideal diode between the main battery/system node and the XIAO BAT lead
• USB-C firmware updates through the XIAO
• USB-C battery charging through the BQ25798
• One external charge LED
• Optional MeshCore-supported BME680 environmental I2C port
• Direct controlled-impedance RF path from E22 ANT to board-edge SMA
• XIAO-controlled TPS61088 enable for radio power sequencing
• 4-layer controlled-impedance PCB

Solar guidance

• 6 V class panel
• 20 W target for permanent deployment
• BQ25798 must be configured and validated against the selected panel's actual Vmp, Voc and Imp
• Installer must verify Vmp, Voc, Imp and cold-weather Voc

Removed from Rev A

• MAX17048 fuel gauge and battery percentage estimation
• Power button
• eFuse
• Radio load switch
• Pogo pins
• SWD connector
• Multi-wire XIAO harness
• Extra LEDs beyond the charge LED
• Solar/USB-present telemetry
• Battery reverse-polarity circuit
• Radio-disable jumper
• Display, GPS and non-MeshCore accessory sensors
• Bench-test jumpers, simulated-temperature bypass networks and mode-selection test footprints

Power summary

• Battery: protected 1S 3.6/3.7 V nominal, 4.20 V maximum, 10-20 Ah class
• Battery discharge capability: at least 5 A continuous, 8 A transient preferred
• Maximum charge current: 2 A
• Charge temperature sensing: battery-mounted 10 kOhm NTC; target policy suspends charging below 0 C and at/above 45 C
• Battery telemetry: BQ25798 battery voltage and charger-state measurements; no dedicated SOC fuel gauge in Rev A
• E22 rail: 5.0 V nominal
• TPS61088 rail design target: 2 A continuous
• TPS61088 inductor: Coilcraft XAL7030-222MEC, 2.2 uH
• BQ25798 inductor: Coilcraft XAL7070-222MEC, 2.2 uH
• E22 local bulk capacitance: 330-470 uF plus ceramics

Canonical documents

• docs/DESIGN_FREEZE_REV_A.md
• docs/CURRENT_STATUS_REV_A.md
• docs/WIRING_BLUEPRINT.md
• docs/ELECTRICAL_DESIGN_REV_A.md
• docs/LOCKED_COMPONENTS_REV_A.md
• docs/FINAL_POWER_CALCULATIONS_REV_A.md
• docs/SOLAR_DESIGN_GUIDE_REV_A.md
• docs/PCB_NET_CLASSES_REV_A.md

Earlier concept documents are superseded where they conflict with the design-freeze document.

Repository layout

2Watt-Project/
├── docs/              Engineering specifications and calculations
├── hardware/          KiCad project, symbols, footprints and fabrication files
├── firmware/          Board support and hardware test firmware
├── bom/               Manufacturing and sourcing files
├── production/        Assembly and manufacturing outputs
└── test/              Bring-up procedures and measurements

Local KiCad project

Open the Mac/KiCad project here:

hardware/kicad/RoyalNode/RoyalNode.kicad_pro

Useful local checks:

make validate
make kicad-checks

Remaining work

1. Resolve or formally accept the E22 footprint-library warning through the manufacturing review path.
2. Unblock the Molex edge-launch SMA footprint and final 50-ohm GCPW geometry.
3. Confirm XIAO socket orientation, XT30 polarity and connector mating clearance.
4. Refine power-stage placement from the generated ratsnest.
5. Route the PCB.
6. Run DRC, ERC, JLCPCB DFM and PCBA review.
7. Order Rev A prototypes for production validation.

Safety and regulatory note

The radio hardware may be capable of approximately 33 dBm output. Deployed settings must comply with applicable conducted-power, antenna-gain, EIRP, bandwidth and certification requirements. The battery pack must include suitable internal protection, and deployment must respect the battery manufacturer's permitted charging-temperature range.