Mesh Water Level

Two devices, one link each. The sender sits in a weatherproof box over the water, reads the ultrasonic sensor on a timer, and transmits a short LoRa message with the distance and its battery voltage. The receiver sits indoors within WiFi range (a LoRa link can span a few hundred metres to a few kilometres depending on terrain and antennas), acknowledges each reading, and posts it to a Bayou feed as distance_meters and battery_volts.

Illustration courtesy Jacob Lloyd

Prices are approximate (USD, 2026) and shown only for budgeting. Where a part is generic, the spec that matters is listed instead of a single product, so you can buy from whichever supplier ships to you.

The Rook is an open-hardware carrier board designed by Edge Collective / PVOS. It pairs an nRF52840 “pro-micro” module with a Seeed Wio-SX1262 LoRa radio, a small OLED screen, a user button, a power switch, and a JST battery connector. There are three ways to get one.

Check the OLED's pin order before soldering. The Rook's OLED header is wired VCC · GND · SCL · SDA, left to right. The labels printed above the four pins on your display must read in that same order, as they do on this module. Many look-alike OLEDs put GND first, and plugging one of those in reverses the power and can destroy the display.

Only three wires go between the sensor and the Rook. The MB7383 runs freely, sending a frame like R0742 (742 mm) about six times a second at 9600 baud. The Rook listens on its RX1 pin and never talks back. Power comes in through the pro-micro's USB-C port from the solar panel. The battery plugs into the Rook's JST socket.

About charging: the solar panel's 5 V goes into the pro-micro's USB-C port, and the pro-micro's built-in charger tops up the battery. That charger is small (about 100 mA on a nice!nano), so a bigger panel won't charge any faster. A larger battery gives you more cloudy days in reserve, not faster charging. A 10000 mAh cell is a sensible choice for winter or for shaded sites.

The sensor measures the distance down to the water, so level = (height of sensor above your datum) − distance_meters. Record the mount height once at install time. Mount the box level, so the sensor points straight down over open water.

1. Drill the bottom of the box for the sensor. Thread the MB7383 through a ¾″ PVC fitting or locknut so its face points down, and seal the joint.
2. Fit a cable gland in the side or bottom of the box for the solar panel's USB cable. Keep all openings facing down so rain can't run in.
3. Mount the box so the sensor face is at least 0.5 m above the highest water you expect. The MB7383 reads anything closer as 50 cm. Its maximum range is 10 m.
4. Face the panel toward the equator (south in the northern hemisphere), tilted up and unshaded for as much of the day as you can manage.
5. Test in air first: aim the sensor at the floor from a known height and confirm the OLED reads it to within about 1 cm.

The Heltec needs no wiring: attach its LoRa antenna, plug it into USB power, and place it indoors where it gets WiFi, as close to the sensor as you can, ideally high up by a window facing the sensor. Once configured, it reconnects to WiFi by itself after a power cut.

Everything is done from one web page in Chrome or Edge on a desktop computer: edgecollective.io/micro-config. It walks through these steps in detail.

1. Flash the gateway. Plug in the Heltec and flash the v3-ultrasonic receiver firmware straight from the browser.
2. Flash the Rook (skip if it came pre-flashed). Double-tap reset, and a NICENANO drive appears. Drag the .uf2 file onto it.
3. Pair them. With both powered up side by side, cycle each OLED to its Advert page with short presses, then long-press to broadcast. Each device adds the other as a contact.
4. Point the sender at the gateway. In the Rook's serial console, run:

   list
   target Receiver

5. Put the gateway on WiFi from its serial console:

   set wifi_ssid your-network
   set wifi_password your-password
   reboot

6. Point it at your own Bayou feed. Create a feed at bayou.pvos.org (see Data in Bayou), then enter its two keys:

   set bayou_public_key YOUR_PUBLIC_KEY
   set bayou_private_key YOUR_PRIVATE_KEY

7. Optional: change how often readings are sent with set interval 300 (seconds, minimum 10), and give the node a name with set name Dock-North.

To check it's working, run send on the Rook to force a reading now, and status on the gateway to see the WiFi and Bayou status and the last reading received.

From sensor to database

Each reading changes shape twice on its way into Bayou:

[SENSOR] node_id=1 dist=1.234m
 batt=3.87V fwd_hops=0 fwd_path=none

{
  "private_key": "YOUR_PRIVATE_KEY",
  "node_id": 1,
  "distance_meters": 1.234,
  "battery_volts": 3.870,
  "aux_1": 0,
  "aux_2": 0,
  "log": "path=none route=DIRECT",
  "source": "Sensor"
}

{
  "id": 2490734,
  "timestamp": "2026-07-20T09:04:31.832Z",
  "parameters": {
    "distance_meters": 1.234,
    "battery_volts": 3.87,
    "node_id": 1,
    "aux_1": 0, "aux_2": 0,
    "log": "path=none route=DIRECT",
    "temperature_c": null,
    "…": "every other field, null"
  }
}

What the gateway sends

Posting to Bayou yourself

POST/data/<public_key>/ accepts JSON (Content-Type: application/json) or an ordinary form post. It must include private_key and can include any of the fields below. Unknown fields are silently dropped, and omitted fields are stored as empty. The server records the time a reading arrives. You can't send your own timestamp, so old data can't be backfilled. A successful post returns 200 Measurement recorded. A wrong key returns 400 Private key mismatch.

You can test a new feed from a laptop before any hardware is involved:

curl -X POST https://bayou.pvos.org/data/YOUR_PUBLIC_KEY/ \
  -H 'Content-Type: application/json' \
  -d '{"private_key":"YOUR_PRIVATE_KEY","node_id":1,"distance_meters":1.72,"battery_volts":3.9}'

Reading data out

Every read address needs only the public key, so you can share them freely. The JSON addresses allow cross-origin requests (CORS), so any web page can fetch a feed directly. Replace <key> with the feed's public key and <node> with a sender's node_id.

Every JSON response has the same shape: {"feed_pubkey", "feed_name", "data": [ {"id", "timestamp", "parameters": {…}} ]}. Each reading's parameters contains all the accepted fields, with null for any that weren't sent. Timestamps are UTC. Bayou has no filtering by date range: fetch the latest N with limit, or download the full CSV.