ChiMesh

Off-grid Chicago. A solar-powered LoRa mesh that runs without the internet, the grid, or anyone's permission.

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ChiMesh

Chicago LoRa Meshtastic mesh — proof-of-mesh build. Three solar-powered RAK4631 nodes in weatherproof IP65 enclosures that prove multi-hop LoRa routing across the city. About ~$62 per node (so ~$186 for the proof batch of three), plus ~$25 in shared consumables (wire, JST, solder, heat-shrink) and any one-time tools you don't already own. No lamp disguise yet — that's v2 once the protocol is proven.

Two non-negotiable rules.

  1. LiFePO4, not Li-ion. Chicago winters charge below 0°C. Li-ion cells permanently plate lithium when charged that cold and can fail dangerously by summer. LFP is non-negotiable for any outdoor ChiMesh node.
  2. Never plug USB-C into the RAK19003 while the LFP cell is wired into the JST. The RAK19003's onboard charger is Li-ion only (4.2 V termination) and will overcharge an LFP cell (3.65 V max). The safe re-flash procedure is in §6.1: unplug the JST-PHR-2, plug USB-C, do your work, unplug USB-C, plug the JST back in.

01. Configure #

Pick what you have or plan to buy and the guide below adapts. Choices save automatically.

02. Shopping list #

The total below counts core parts per node only. Multiply by your planned node count — minimum 3 to actually prove multi-hop routing (otherwise there's no chain to forward through). The consumables and tools categories show one-time / shared items and are excluded from the per-node total.

03. Assemble #

Total time: ~30 minutes per node, once parts are in hand.

3.1 Tools you'll need #

One-time tools, not per-node — most builders already own them. See the shopping list for specific picks if you don't:

  • Temperature-controlled soldering iron + 60/40 rosin-core solder (0.8 mm)
  • Heat-shrink tubing (2–8 mm assortment) + heat gun or lighter
  • Wire strippers + flush cutters for 22 AWG
  • JST crimp tool (or buy pre-crimped JST-PHR-2 pigtails and skip this)
  • Digital multimeter — for verifying LFP cell voltage (3.2–3.65 V) and panel output (~6.5 V Voc) during troubleshooting
  • Drill + bits — 6 mm for the SMA bulkhead hole, 12 mm for the M12 cable gland (a step bit makes cleaner holes in ABS)
  • Phillips #1 screwdriver for the enclosure lid

3.2 Wiring overview #

One signal path with two sub-paths:

Solar panel  →  TP5000 (LFP jumper set!)  →  LiFePO4 cell  →  JST-PHR-2  →  RAK19003  →  RAK4631
RAK4631 IPEX  →  pigtail  →  SMA bulkhead  →  915 MHz antenna

3.3 Build steps #

DO NOT INSTALL THE LFP CELL UNTIL SECTION 06. Sections 04 and 05 want you connecting USB-C to the RAK19003 for flashing and provisioning. The RAK19003's onboard charger terminates at 4.2 V (Li-ion), which will overcharge an LFP cell (3.65 V max). Cell goes in AFTER firmware + config are done.

  1. Set the TP5000 jumper to LFP (3.6 V). This is the single most important step. The board ships with the jumper in either position; LFP termination is usually labeled 4.2/3.6 or Li-ion/LiFePO4. Wrong jumper = dead cell in weeks.
  2. Solder the solar panel leads to the TP5000 IN+ / IN- pads. Red to +, black to -. Heat-shrink the joint — the enclosure isn't fully sealed if the panel cable enters with bare conductors.
  3. Solder the LFP cell holder leads to the TP5000 BAT+ / BAT- pads. Don't insert the cell yet.
  4. Crimp a JST-PHR-2 onto a short pair of 22 AWG wires, then solder the other end of those wires to the TP5000's BAT+ / BAT- pads (in parallel with the cell-holder leads). This is the output that feeds the RAK19003.
  5. Snap the RAK4631 onto the RAK19003 Mini Base. Align the silk-screen markers, press until the board-to-board connector seats fully.
  6. Connect the IPEX pigtail. The u.FL connector on the RAK4631 is fragile — press straight down with a thumbnail until it clicks. Mount the SMA bulkhead end through the drilled hole in the top of the enclosure (panel nut on the outside). SMA, not RP-SMA — they look identical but won't mate with a LoRa antenna.
  7. Plug the JST-PHR-2 from the TP5000 into the RAK19003 battery input. It only fits one way. Leave the cell holder EMPTY for now — power for sections 04 and 05 comes from USB-C, not the battery path.
  8. Mount everything inside the enclosure. Foam-tape the TP5000 to one wall, the RAK19003 + Mini Base to the opposite wall, the cell holder along the floor (empty). Route the panel cable out through the M12 gland.
  9. Visual sanity check. Antenna is vertical when the enclosure is mounted in its final orientation. No bare wire near the SMA bulkhead. Cell holder is empty and ready.

Rooftop note. Grounding is a real concern when the antenna is your highest point. Add a gas-discharge tube (GDT) lightning arrestor on the SMA line before the radio — cheap insurance for a board you can't easily reach.

✅ Checkpoint: Boards mounted, antenna threaded through enclosure wall, panel cable sealed at the gland, cell holder empty and ready for sections 04–05.

04. Flash firmware #

ChiMesh runs stock Meshtastic firmware. We're not forking — for v0 the value is in deployment + config conventions, not custom firmware.

4.1 Open the web flasher #

In Chrome or Edge (Web Serial isn't in Firefox/Safari), open:

https://flash.meshtastic.org

4.2 Connect and flash #

  1. Plug the RAK19003's USB-C into your computer.
  2. Click Select Device. Pick RAK4631 from the dropdown.
  3. Pick the latest stable Meshtastic 2.5.x build.
  4. Pick Region: US (default; adjust if you're outside the US).
  5. Click Flash, allow the browser's serial-port prompt.
  6. Wait ~30 seconds. The board reboots into the Meshtastic firmware automatically.

✅ Checkpoint: Flasher prints "Done" and the RAK19003 LED settles into a slow heartbeat pattern.

05. Configure node #

You can configure either via the official Meshtastic app over Bluetooth, or via the meshtastic CLI over USB. The CLI is faster for scripted multi-node setup — recommended for ChiMesh since you're provisioning at least 3 nodes identically.

5.1 Install the Meshtastic CLI #

pip install --upgrade meshtastic

You should see meshtastic-python 2.5.x or newer.

5.2 Provision the node #

Use the bundled provisioner — it walks one USB-connected node through the standard ChiMesh config:

scripts\cli\provision-node.ps1 -NodeName chimesh-001

Or set each field manually:

meshtastic --set lora.region US
meshtastic --set device.role ROUTER_CLIENT
meshtastic --ch-set name "ChiMesh-Test" --ch-index 0
meshtastic --set-owner chimesh-001

Role note (ROUTER). ROUTER means this node relays every packet it hears but never originates user messages. Reserve for true backbone nodes — usually 1 per metro area. For most ChiMesh deployments ROUTER_CLIENT is better because it both relays AND lets you chat from this node.

Role note (CLIENT). CLIENT is for portable / handheld use — the node sleeps aggressively to save battery. A sleeping CLIENT will not forward packets. Do NOT use this role for your fixed proof nodes; pick ROUTER_CLIENT for those.

Region note (EU 868). EU duty-cycle rules limit each device to ~1% airtime on most sub-channels. Meshtastic respects this in firmware, but expect slower message throughput than US 915.

5.3 Confirm #

meshtastic --info

You should see the region you picked, the role you picked, and channel 0 named ChiMesh-Test.

✅ Checkpoint: meshtastic --info returns region + role + channel exactly as expected.

06. Deploy #

6.1 Install the LFP cell — finally #

With firmware flashed and config written, unplug USB-C from the RAK19003. Now insert the LFP cell into the holder. The RAK19003 red LED should blip briefly as the board powers up from the TP5000's BAT output. From this point forward, never plug USB-C in unless you've first unplugged the JST-PHR-2 from the RAK19003 — the onboard charger will overcharge LFP otherwise.

If you need to re-flash later: power down (unplug JST), plug USB-C, flash, unplug USB-C, plug JST back in. Tedious but safe.

6.2 Placement strategy #

For proof-of-mesh, the 3 nodes have to be positioned so at least one pair cannot hear each other directly. Otherwise you've built a 1-hop network and proven nothing about multi-hop routing.

A workable Chicago layout:

Node Suggested location Why
Node A High-rise apartment window or balcony Gateway altitude — sees both B and C
Node B Friend's apartment / office, ~1–3 km away Far enough it can't reach C directly
Node C Second remote location, ~1–3 km from B in a different direction Forces traffic through A

Apartment-window note. Indoor through low-E (energy-efficient) glass costs ~10–15 dB of signal. If you have access to a balcony or an exterior fence/eave, use it — Chicago's lake-effect glass is particularly bad for 915 MHz. Antenna outside the window beats antenna inside, every time.

Rooftop note. Strongest placement. Aim the solar panel south at ~41° tilt (Chicago's latitude). Mount the enclosure on the north side of any obstruction so the antenna stays clear of metal HVAC, parapets, and roof-edge railings.

Ground-pole note. Range from a ground-level node is roughly half of an elevated one — buildings, cars, and foliage block line-of-sight. Useful as a yard pin but not as your gateway node. Don't expect to bridge anything beyond ~500 m.

Fiberglass colinear note. An 8+ dBi fiberglass antenna is heavier, more visible, and needs a real mast or bracket. Pair it with the rooftop deployment only — on a balcony it's overkill and on a window it's structurally awkward.

Solar panel aim. Face south, tilt ~41° (matches Chicago's latitude). Don't lay panels flat — flat panels collect snow and bird droppings, and the December sun angle is so low that flat-mount harvest drops ~30%.

Antenna orientation. Vertical. Most Meshtastic networks are vertically polarized; a sideways antenna costs you ~3 dB instantly.

6.3 Power budget #

Rough draw for the RAK4631 (SX1262 + nRF52840) running stock Meshtastic in continuous receive:

  • SX1262 in RX: ~4.6 mA
  • nRF52840 active (BLE off, CPU lightly loaded): ~3–6 mA
  • Combined at 3.3 V: ~8–12 mA average in steady listen, with brief spikes to ~120 mA on TX bursts.

Over 24 hours that's ~200–280 mAh consumed. The 1500 mAh LFP cell + 5 V / 2 W panel works for Chicago summer — a sunny day harvests ~600–800 mAh, well above draw — but December is tight: 1.5 peak sun hours × 2 W ≈ 150–200 mAh/day in, against ~250 mAh/day out. That's a real-world deficit on the worst weeks, and the reason the v0 panel-aim rule above says "tilt ~41°, never flat." If a node has to survive a Chicago January with no intervention, plan to add a second cell in parallel (3000 mAh total) or step up to a 5 W panel — both are documented in §08.

✅ Checkpoint: All 3 nodes deployed, solar panels facing the sky, antennas vertical, enclosure lids closed and sealed.

07. Verify mesh #

7.1 Pair with the Meshtastic app #

Install the Meshtastic app — see https://meshtastic.org/docs/software/apps/ for the official download links. Pair with Node A over Bluetooth (default PIN is 123456 unless you changed it).

7.2 Check the node list #

The app's Nodes tab should list all 3 nodes within a few minutes — A directly (paired to your phone) plus B and C via radio. The gear icon next to each remote node shows hop count: 1 hop = direct, 2 hops = routed through another node.

7.3 The actual test #

Send a text from the app (paired to A) to Node C. If it arrives at C, and the path shows via B in the app, you've proven multi-hop routing.

If every node shows 1 hop, the nodes are too close together — separate them further until at least one pair can't see each other directly.

✅ Checkpoint: A message from your phone (paired to A) reaches C with a via B hop indicator in the app.

7.4 Run the bundled healthcheck #

scripts\cli\healthcheck-mesh.ps1

Connects to whichever node is on the USB cable, queries --info and --nodes, and reports region, role, channel-0 name, and the count of known peers. Use it as a one-shot sanity check before calling the deployment done.

08. Troubleshooting #

Nothing comes up on the web flasher #

  • Chrome or Edge only — Web Serial isn't in Firefox/Safari.
  • Try a different USB-C cable. Many "charging only" cables don't carry USB data.
  • On Windows, check Device Manager for the COM port; if it's missing, install Nordic's USB driver.

Flashed, but no LED activity #

  • The RAK19003 red LED only lights when current is drawn — if the cell is dead or the jumper is wrong, the board sits at 0 V.
  • Check cell voltage with a multimeter: a healthy LFP reads 3.2–3.65 V.
  • Confirm the TP5000 jumper is set for LFP (3.6 V), not Li-ion (4.2 V).

Nodes can't see each other #

  • Verify all nodes are on the same region (meshtastic --info shows lora.region).
  • Verify all nodes are on the same channel name AND PSK.
  • Move one node within 10 m of another to rule out a config bug vs a range issue.

Solar isn't keeping up #

  • Confirm the panel is generating: disconnect from the TP5000, measure open-circuit voltage in sunlight — should be ~6.5 V Voc (closer to ~5 V once it's loaded by the TP5000).
  • Confirm the TP5000 is charging: re-connect, measure across the cell — should rise toward 3.6 V over an hour of sun.
  • December low-light is the close case. If a node won't survive the worst week, upgrade to a 5 W panel, or add a second LFP cell in parallel (~3000 mAh total) to ride through low-light stretches.

Radio not responding via CLI #

scripts\cli\healthcheck-mesh.ps1 -Verbose

Reads the connected node and prints any error states from --info.

Reference #

Summary stack #

Layer What it is
Radio Semtech SX1262 LoRa, 915 MHz US ISM
MCU Nordic nRF52840 (ARM Cortex-M4F @ 64 MHz)
Board RAK4631 (RAK Wireless WisBlock Core) on RAK19003 Mini Base
Firmware Meshtastic 2.5.x (stock, unmodified)
Mesh protocol Meshtastic managed flood routing
Power 5 V / 2 W solar → TP5000 (LFP-configured) → LiFePO4 18650
App / config Meshtastic mobile/desktop over BLE, or meshtastic CLI over USB
Enclosure IP65 ABS junction box, M12 gland for solar lead