Meshthingy

meshthingy

An off-grid LoRa mesh communicator — a pocket-sized ESP32-S3 node that sends text and GPS position over kilometres of open ground, with no cell tower, no SIM, no subscription, and no internet.

_{KiCad 10 · 2-layer · 71 × 46 mm · ESP32-S3 + SX1262 LoRa · USB-C · Li-Ion · hardware rev R1}

[!WARNING] Rev R1 is currently in fabrication — nothing here has been tested yet. The schematic and layout are finished and pass DRC, but no board has been assembled or powered up. Everything in this README (pin map, charger settings, power latch behaviour, assembly notes) describes the design as intended and may change after bring-up. Build one at your own risk.

Project status

What this board is for

Phones stop working the moment you leave coverage. meshthingy doesn't need coverage — it is the network.

Each board is one node in a self-healing Meshtastic mesh. Nodes talk directly to each other over licence-free LoRa radio, and every node automatically relays traffic for its neighbours. Two units give you a private long-range walkie-talkie for text; a handful scattered across a valley, a campsite, a ridgeline, or a city block give everyone in that area a shared messaging network that keeps working when nothing else does.

Because LoRa trades bandwidth for range and power, a node runs for days on a small Li-Ion cell and reaches several kilometres line-of-sight — far past Wi-Fi or Bluetooth, and without the power budget a cellular radio demands.

Typical uses: hiking and backcountry trips, sailing, off-road convoys, festival and event crews, neighbourhood emergency preparedness, and as a low-cost long-range telemetry link for remote sensors.

The onboard GPS, environmental and motion sensors mean a node is useful even with nobody holding it — drop one on a hilltop as a solar-powered repeater and it becomes a weather station that also extends everyone's range.

Features

• ESP32-S3-WROOM-1 — dual-core MCU with Wi-Fi and Bluetooth LE for phone pairing, native USB
• HT-RA62 LoRa module (SX1262) — long-range sub-GHz radio on an SMA edge-mount connector
• ATGM336H GNSS — position reporting on a U.FL active antenna, with a rechargeable backup cell for warm starts
• 0.96" OLED — read messages without a phone
• BME280 — temperature, humidity, barometric pressure, on a slotted island away from board heat
• LIS3DSH accelerometer — wake-on-motion and orientation, with interrupt to the MCU
• USB-C charging — BQ24072 Li-Ion charger with power-path, so it runs while charging
• Soft power switch — the lever's push turns the node on; firmware holds power and can turn itself off
• JST-PH battery connector — standard single-cell Li-Ion / LiPo, polarity marked on the silkscreen
• Vibration motor driver — SI2302 low-side switch with flyback diode, for silent alerts in a pocket
• Buzzer, status LED, and a side lever switch (CW / CCW / push) for headless operation
• Test points on every bus for bring-up and debugging

System architecture

flowchart TB
    subgraph RF["📡 Radio"]
        LORA["<b>U4 · HT-RA62</b><br/>SX1262 LoRa"]
        SMA["J4 · SMA<br/>edge mount"]
        LORA --- SMA
    end

    subgraph CORE["🧠 Core"]
        MCU["<b>U7 · ESP32-S3-WROOM-1</b><br/>Wi-Fi · BLE · dual core"]
    end

    subgraph NAV["🛰️ Navigation"]
        GPS["<b>U2 · ATGM336H</b><br/>GNSS receiver"]
        UFL["J3 · U.FL<br/>active antenna"]
        EEP["U8 · AT24CS32<br/>EEPROM"]
        BAT2["C13 · XH414H<br/>backup cell"]
        UFL --- GPS
        GPS -->|"private I²C"| EEP
        BAT2 -.->|"keeps time"| GPS
    end

    subgraph IO["🔌 I²C peripherals"]
        OLED["U1 · 0.96in OLED"]
        BME["U9 · BME280<br/>temp · humidity · pressure"]

Power path

USB-C and the battery both feed a power-path charger, so the node keeps running while it charges and switches over seamlessly when USB is unplugged. The 3.3 V buck converter is only enabled while something holds the power latch on.

flowchart LR
    USB["<b>J1</b><br/>USB-C<br/>5 V in"] -->|VBUS| CHG
    BATT["<b>J2</b><br/>Li-Ion cell<br/>JST-PH"] <-->|charge / discharge| CHG
    CHG["<b>U6 · BQ24072</b><br/>Li-Ion charger<br/>+ power path"] -->|VSYS| BUCK
    LATCH["<b>Power latch</b><br/>Q2 · Q3"] -->|BUCK_EN| BUCK
    BUCK["<b>U3 · TPS62046</b><br/>3.3 V step-down<br/>via L2"] -->|"+3V3"| RAIL

    BTN["Lever push"] -.-> LATCH
    PG["USB present<br/>(PGOOD)"] -.-> LATCH
    HOLD["IO9 · SYS_EN<br/>(firmware hold)"] -.-> LATCH

    RAIL["<b>+3V3 rail</b>"] --> M1["ESP32-S3"]
    RAIL --> M2["LoRa"]
    RAIL --> M3["GNSS"]
    RAIL --> M4["Sensors + OLED"]
    RAIL --> M5["Buzzer + vib motor"]

    classDef src fill:#dc2626,stroke:#991b1b,color:#fff,stroke-width:2px
    classDef conv fill:#ea580c,stroke:#c2410c,color:#fff,stroke-width:2px
    classDef rail fill:#16a34a,stroke:#15803d,color:#fff,stroke-width:2px
    classDef load fill:#475569,stroke:#334155,color:#fff
    classDef ctl fill:#64748b,stroke:#475569,color:#fff
    class USB,BATT src
    class CHG,BUCK conv

Turning on and off

The buck converter's enable is driven by a PNP switch (Q2) from a latch node that is pulled low by any one of three sources, each isolated by a 1N4148WS:

1. Lever push (U5, D7) — pressing it powers the board up.
2. USB present (PGOOD from U6, D4) — the node is always on while plugged in.
3. Firmware hold (IO9 / SYS_EN through Q3) — firmware must drive IO9 high early in boot, or the board switches off again when the lever is released. Driving IO9 low (with USB unplugged) powers the node down.

The MCU can read the lever push on IO10 and USB presence on IO17 (both through diodes, active low, use internal pull-ups). The latch diodes must stay low-leakage silicon parts — Schottkys leak enough to half-enable the buck when off.

Charger settings (U6 · BQ24072)

VSYS follows the battery (and tracks VBAT + 225 mV while charging). IO8 reads VSYS / 2 through R16/R17 — that is the battery voltage when running on battery.

Board

Everything routes on two layers, which keeps this a cheap board to order from any prototype fab at standard tolerances.

Assembled views

Front — LoRa and GNSS modules, ESP32-S3, USB-C, buzzer, GPS backup cell, motor driver

Back — labelled test points for every bus, vibration motor pads (JP1, silkscreen VBR), repo QR code

PCB layer views

Copper, silkscreen and board outline, plotted straight from the layout. The back view is mirrored so its silkscreen reads the right way round.

F.Cu + F.SilkS — signal routing over the front ground pour; B/R are the boot and reset pads

B.Cu + B.SilkS — mirrored; back pour with the test-point field and motor pads

The RF section is deliberately sparse: the pours are cut back under the antenna connectors, the ESP32's PCB antenna hangs over a board cut-out, and the GPS keepout is marked on the silkscreen so nothing gets placed under it during assembly.

Regenerate the 3D renders and layer plots after any layout change (the renders are trimmed with ImageMagick):

kicad-cli pcb render --output /tmp/f.png --side top    --quality high --width 2000 --height 1300 meshthingy.kicad_pcb
kicad-cli pcb render --output /tmp/b.png --side bottom --quality high --width 2000 --height 1300 meshthingy.kicad_pcb
magick /tmp/f.png -trim +repage -bordercolor none -border 24 docs/meshthingy-f.png
magick /tmp/b.png -trim +repage -bordercolor none -border 24 docs/meshthingy-b.png

kicad-cli pcb export svg --output docs/layers-front.svg \
  --layers "F.Cu,F.SilkS,Edge.Cuts" \
  --page-size-mode 2 --exclude-drawing-sheet --check-zones --mode-single \
  meshthingy.kicad_pcb

kicad-cli pcb export svg --output docs/layers-back.svg \
  --layers "B.Cu,B.SilkS,Edge.Cuts" --mirror \
  --page-size-mode 2 --exclude-drawing-sheet --check-zones --mode-single \
  meshthingy.kicad_pcb

Pin map

IO3, IO35–37, IO45 and IO46 are left unconnected (strapping pins and the octal-PSRAM pins on R8 module variants).

Schematic layout

The design is hierarchical — root sheet meshthingy.kicad_sch:

Bill of materials

The curated BOM is bom/meshthingy-bom.csv: 36 board lines / 76 placed parts, plus the off-board items (battery, antennas, vibration motor). It adds manufacturer part numbers where the footprint fixes the part, and a notes column with ratings and the reason behind each value.

Still to pin down before ordering parts:

• U7 — pick the module variant (e.g. -N8R2, -N16R8). Avoid the 1.8 V …V variants: IO47 and IO48 are in use.
• C16, C25 — voltage rating (≥ 10 V low-ESR tantalum).
• U4 — HT-RA62-HF for 863–928 MHz, HT-RA62-LF for 433/470 MHz.

Test points and solder jumpers are left out — they are PCB features, not parts.

A print-ready A4 copy with kitting checkboxes and the open items highlighted is rendered from the CSV with python bom/render_bom_pdf.py (needs pip install weasyprint) and written to bom/meshthingy-bom.pdf. For hand assembly, open bom/ibom.html in a browser — an interactive BOM that highlights each part's position on the board.

Building it

Open meshthingy.kicad_pro in KiCad 10 or newer. All custom symbols and footprints live in libs/ and are referenced through ${KIPRJMOD}, so the project is self-contained — clone and open, nothing else to install.

Generate fabrication files from the command line:

# Gerbers + drill, ready to zip and upload to a fab
kicad-cli pcb export gerbers --output fab/ meshthingy.kicad_pcb
kicad-cli pcb export drill   --output fab/ meshthingy.kicad_pcb

# Raw schematic BOM and pick-and-place
kicad-cli sch export bom       --output fab/bom-raw.csv meshthingy.kicad_sch
kicad-cli pcb export pos       --output fab/pos.csv meshthingy.kicad_pcb

# Design rules check
kicad-cli pcb drc --output fab/drc.rpt meshthingy.kicad_pcb

Generated outputs are gitignored — regenerate them, or attach them to a release tag.

Assembly notes

U3 (TPS62046) has a PowerPAD that must be soldered to the ground pad under it. The pad is a copper shape on the board rather than part of the footprint, so it has no paste aperture — tin it by hand, or add paste to the stencil, before reflowing U3.

JP3 and JP4 are three-way solder jumpers that select which OLED pin gets +3V3 and which gets GND, so the footprint accepts display modules with either pinout. They ship unbridged — bridge them to match the module you source before expecting the display to light up. Never bridge all three pads of one jumper.

JP1 on the back (silkscreen VBR) is not a jumper. It's the pair of solder pads for the vibration motor. Solder a coin or pager-style motor's leads across it: the pad on the +3V3 side takes the red lead and the pad on the Q4 drain side takes the black lead. D9 clamps the motor's flyback, so the motor runs straight off the +3V3 rail.

J2 has + / − marked on both sides. JST-PH battery leads are not wired the same way by every vendor, and there is no reverse-polarity protection — check the plug before connecting a cell.

B and R on the front are the BOOT and RESET pads. To put the ESP32-S3 into the ROM bootloader, short B while you tap R.

Firmware

🚧 Work in progress. There is no firmware for this board yet — it will target Meshtastic on the ESP32-S3 once the first boards are back from the fab and brought up. Until then, the pin map above is the reference for anyone writing a variant.

Repository notes

.history/ is KiCad 10's Local History — a separate nested git repository of autosaves. It is gitignored and should stay that way. Delete it freely if you don't need the local undo history.

_{Meshtastic® is a registered trademark of Meshtastic LLC. This is an independent hardware design and is not affiliated with or endorsed by Meshtastic LLC.}