The BLE Sensor Listener.

What it does.

Plenty of cheap Bluetooth sensors, Govee thermometers and about a hundred and twenty other models, already shout their readings into the air every few seconds. This node listens for them and harvests every measurement each one broadcasts, temperature and humidity, but also soil moisture, conductivity, CO₂, light, air quality, battery and signal, averages the chatty ones into steady numbers, and pushes them to an endpoint you own: your own webhook, an MQTT broker, or Open Agriculture Technology. Because it only listens, there is nothing to wire and nothing to solder, the sensor and the chip never touch.

By default it reports only the devices that broadcast a real sensor reading, so a room full of phones and stray Bluetooth gadgets stays quiet. Want just your sensors, or to include a beacon or a smart lock? Give it an allow-list of the addresses you care about during setup, and it reports those and nothing else.

That is the Collect layer made as small and cheap as it honestly gets. The value is in what you do with the reading later; the job here is just to get it flowing, reliably, to a place that is yours.

Flash it.

Plug your board in, find it below, and press its button. Each button installs the image built for that exact board, and the installer checks the chip really matches before it writes anything, so you can't flash the wrong one.

You'll need a data USB cable (not charge-only) and Chrome or Edge on a computer. Once it's flashed, set it up from any phone or laptop.

What you need.

About ten dollars of parts, most of which you may already have:

How it works.

Four steps, and only the middle one is the chip's job:

1. Your sensor broadcasts its reading over Bluetooth, the way it already does.
2. The node hears every nearby sensor it recognises and averages the readings over a window you set.
3. On a timer, it pushes one tidy packet per cycle to your endpoint.
4. Your dashboard, alert, or store reads it. Your data, your place.

It pushes wherever you point it, Open Agriculture Technology, your own Home Assistant, a broker you run, or a webhook you wrote this afternoon. The node keeps working even if Open Agriculture Technology disappears. That's the own-your-data rule in hardware.

Set it up.

All the setup happens on the device's own page, nothing to install, and it works with no internet, which is exactly what you want if you flashed a few at the extension office to take home.

1. Power the node from any USB charger or your computer.
2. On your phone or laptop, join the Wi-Fi network OAT-Setup-XXXXXX (open, no password). A setup page opens by itself; if not, visit http://192.168.4.1.
3. Sign in, fill in your device name, Wi-Fi, and where the readings should go, then press Save & Connect. It joins your Wi-Fi right away and shows you its new address, no reboot, no hunting for it.
4. Open the node's Status page and press Push now. A green “OK” means a reading just reached your endpoint. Done.

The setup network stays on, so you can rejoin any time to change a setting, and your settings survive reboots. A fresh firmware flash wipes them clean, on purpose, so a re-used board never carries the last owner's Wi-Fi or endpoint.

On a native-USB board (C3 / C6 / S3) you can skip the Wi-Fi form and set it up over the browser console instead: connect, then type wifi, endpoint, and name. Handy if the setup network is being fussy.

Curious what those readings look like once they land? See the live demo →, a dashboard you can open right now, no sign-in. And when you flash your own, the test endpoint is the quickest way to prove it is talking: point the listener at it and watch your first message arrive, checked against the standard.

Open the printable setup card (PDF)

A one-page field card with the steps and blanks to write each node's settings, print a stack before a workshop, or tuck one in with each board you hand out.

What it sends.

Two kinds of message, both tiny. Every cycle the node sends a batch of readings, one entry per measurement each sensor reports, in canonical units (°C, %RH, ppm, lx…) so the receiver never has to guess; every 60 seconds it sends a lean heartbeat reporting its own health, so your endpoint can tell “alive but quiet” from “dead.” Both carry a schema tag (oat-ods/0.3) so you can route and version them. Big batches are split into several small signed posts automatically, so a busy node never overruns a small chip:

{
  "schema": "oat-ods/0.3",
  "msg_type": "batch",
  "sent_at": "2026-07-01T04:26:00Z",
  "seq": 2000006,
  "source": { "tier": "oat-ble-listener", "gateway_id": "gb-c6",
              "fw": "OAT-BLE-Listener/1.4.8" },
  "messages": [
    { "observed_at": "2026-07-01T04:26:00Z",
      "stream": { "id": "A4:C1:38:9E:AB:CD", "name": "GH2 North air",
                  "location": "Greenhouse 2 / North bench" },
      "measurement": "temperature", "value": 23.41, "unit": "Cel",
      "agg": { "window_s": 60, "samples": 9, "method": "mean" },
      "source": { "physical_id": "A4:C1:38:9E:AB:CD",
                  "brand": "Govee", "model": "H5075", "rssi": -67 } },
    { "observed_at": "2026-07-01T04:26:00Z",
      "stream": { "id": "A4:C1:38:9E:AB:CD", "name": "GH2 North air" },
      "measurement": "humidity", "value": 58.7, "unit": "%RH",
      "agg": { "window_s": 60, "samples": 9, "method": "mean" } },
    { "observed_at": "2026-07-01T04:26:00Z",
      "stream": { "id": "AA:BB:CC:00:11:22", "name": "Bed 3 soil" },
      "measurement": "soil_moisture", "value": 34.0, "unit": "%",
      "agg": { "window_s": 60, "samples": 7, "method": "mean" },
      "source": { "physical_id": "AA:BB:CC:00:11:22",
                  "brand": "Xiaomi", "model": "HHCCJCY01", "rssi": -71 } }
  ]
}

{
  "schema": "oat-ods/0.3",
  "msg_type": "status",
  "observed_at": "2026-07-01T04:26:00Z",
  "state": "online",
  "source": { "tier": "oat-ble-listener", "gateway_id": "gb-c6",
              "fw": "OAT-BLE-Listener/1.4.8" },
  "health": {
    "uptime_s": 315, "boot_count": 2, "reset": "poweron",
    "free_heap": 184200, "min_free_heap": 172400, "largest_block": 106496,
    "rssi": -74, "wifi_reconnects": 0, "push_ok": 5, "push_fail": 0,
    "transport": "https", "tls_ok": true, "chip": "ESP32-C6",
    "temp_c": 61.6, "loops_per_sec": 993,
    "lan_ip": "192.168.1.37", "ssid": "BarnWiFi", "mdns": "oat-gb-c6.local",
    "ble_seen": 886, "ble_decoded": 886, "ble_matched": 663
  }
}

Want the whole format, both message types, every field, and the full measurement vocabulary? See the developer reference, or read the machine-readable JSON Schema.

Supported boards.

The firmware needs both Wi-Fi and Bluetooth. We build a ready image for each board below; you pick yours on the flasher and the installer checks it matches before writing. The rule is support broad, recommend narrow.

New to these chips? The ESP32 family field guide explains the differences and which one to buy. A blessed buy-list with exact boards and links is being finalised.

For makers & trainers.