OnMeters Documentation

Everything you need to set up, connect and integrate your Metron optical reader.

Quick start

1. Place the magnetic optical head over the round IR port on your meter's front panel. It self-aligns and holds.

2. Power: the device runs wire-free on its coin cell battery. For permanent installation (or WiFi mode, which uses more power), connect any USB-C supply — a phone charger works.

3. The status LED blinks while reading. Within 60 seconds the first full readout completes.

4. Connect: the device starts in Bluetooth mode — open the web app in Chrome/Edge and tap Connect. Or switch to WiFi mode (below) for the dashboard.

Switching between BLE and WiFi

Only one radio runs at a time. The active mode is stored and survives power cycles. Three ways to switch:

BLE commands

OnMeters exposes a Nordic UART Service (NUS). Write commands to the RX characteristic; responses arrive as notifications on TX, terminated by a newline.

Battery & deep sleep

OnMeters runs wire-free on a CR2450 coin cell. To maximise battery life, enable deep-sleep mode: SLEEP=ON over BLE (or sleep=on via /api/config). The device then wakes on a timer, reads the meter, publishes the data, stays connectable over Bluetooth for 60 seconds, and goes back to deep sleep (a few µA).

Choose how often it reads with INTERVAL= (seconds) or RATE= — for example RATE=24/day for hourly readings or RATE=30/month for a daily reading. Fewer reads = longer battery life.

RGB status LED

HTTP API (WiFi mode)

Base URL: http://onmeters.local (or the device IP).

History log

Every successful read is appended to flash storage (~64 KB ring, oldest entries trimmed automatically). Timestamps come from NTP when the device is in WiFi mode; in battery/BLE mode the epoch is 0 and rows are still ordered. Pull the CSV into Excel, Grafana or a script via /api/history.

Cost calculation

Set your tariff once (PRICE=0.30 + CURRENCY=USD) and OnMeters reports the total energy cost in the JSON (cost_total), and publishes a Home Assistant "monetary" sensor at onmeters/cost.

Mesh relay (beta)

Every Metron embeds its latest reading in its Bluetooth advertisement — like Apple's Find My network. Nearby Metrons overhear it and re-broadcast it (up to 3 hops), with no pairing, router or internet. Connect to any unit and send MESH to see every meter in range of the chain. Each entry carries two identities: the module ID (unique per device, from its radio chip — shown as OM-XXXXXX) and the meter ID (the serial read from the meter itself), so readings stay tracked per meter even if a module is moved.

Installation survey

When installing multiple units, connect to each one and send NEIGHBORS. It listens for 3 seconds and reports every Metron it hears directly, with signal strength and a rough distance estimate:

{ "module_id": "OM-4B22F1",
  "neighbors": [
    { "module_id": "OM-A3F210", "direct": true,  "rssi_dbm": -62,
      "approx_m": 3.2, "link": "strong" },
    { "module_id": "OM-77B4C1", "direct": true,  "rssi_dbm": -84,
      "approx_m": 14.8, "link": "weak" },
    { "module_id": "OM-99D2E0", "direct": false, "via": "relay", "hops": 2 } ],
  "direct_count": 2, "relay_only_count": 1,
  "hint": "some nodes reachable only via relay - links are working" }

If a far unit shows "link": "weak" or doesn't appear at all, place an extra Metron (or any USB-powered unit) roughly halfway between them and run NEIGHBORS again. Distance estimates assume open air — walls and metal meter cabinets shorten real range considerably.

OTA firmware updates

In WiFi mode, open http://onmeters.local/update, choose the official update file downloaded from onmeters.com and click Flash. The device reboots into the new firmware in seconds — no cables, and all settings are kept.

Response format

{
  "device": "OnMeters", "fw": "1.5.0",
  "vbat_mv": 2980, "battery_low": false,
  "interval_s": 1800, "sleep": true,
  "price": 0.30, "currency": "USD", "cost_total": 3854.20,
  "meter": "ISK5MT174-0001", "protocol": "IEC",
  "reads": 42, "age_s": 12, "mode": "wifi",
  "obis": [
    { "code": "1.8.0", "name": "Energy import total",
      "value": "012847.335", "unit": "kWh" },
    { "code": "16.7.0", "name": "Active power",
      "value": "1240", "unit": "W" }
  ]
}

MQTT & Home Assistant

Set a broker once and OnMeters publishes every register plus Home Assistant auto-discovery — sensors appear in HA automatically with correct units and device classes. No YAML needed.

# configure over HTTP (or use BLE: MQTT=192.168.1.10)
curl -X POST http://onmeters.local/api/config \
  -d "mqtt_host=192.168.1.10" -d "mqtt_port=1883" \
  -d "mqtt_user=ha" -d "mqtt_pass=secret"

OBIS reference

Common registers OnMeters decodes (availability depends on your meter):

Firmware updates

Metron updates itself over the air — no cables, no tools. When a new firmware version is released, put one device in WiFi mode, open http://onmeters.local/update, select the update file from onmeters.com and click Flash. The device reboots into the new version in seconds; all your settings are kept.

The rest of your Metrons update themselves. Once one unit runs the new version, it announces it over the mesh — nearby units download it directly from that unit, verify its cryptographic signature, flash, reboot, and pass it onward. A whole building updates from a single flash, with no internet.

Troubleshooting

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