How to build a water trough monitor

See how it goes together

A LoRa radio board and a small battery sit in a weatherproof box with a solar panel in the lid. The box straps to a post by the trough. An ultrasonic sensor on a short arm points down at the water and measures the distance to it.

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Why ranchers want this

In a Utah State University Extension survey from the winter of 2009 to 2010, ranchers spent an average of 22.6 hours, 375 miles and $526.40 a month checking water. Fifteen of them tried satellite monitors that cost $1,800 plus $100 to install. They saved an average of $165 and 11 hours a month. The monitors worked as programmed 88% of the time, and every rancher wanted to keep using one. Only 63% said they'd buy one, mostly because of the upfront cost.

SDSU Extension says producers may spend over $1,500 a year on fuel checking water, and that a dry tank can cost tens of thousands of dollars in lost animals and performance. A 2021 study in Rangelands tracked monitors on a Texas ranch from 2017 to 2019. Depending on the system, they paid for themselves after 8 to 41 skipped trips a year.

Heaton, USU Extension, rancher evaluation slides, USU Extension, remote sensing for stock tanks, SDSU Extension, water monitoring systems for livestock, Walker et al., Rangelands 43(2), 2021

Three years of costs

Hardware plus 36 months of service, before shipping and tax. DIY includes one $154 gateway for the whole ranch. Meterra is $399 with 3 months included, then $10 a month. Ranchbot uses its launch price of $549 and $0.75 a day.

If a public TTN gateway already reaches your troughs, drop the $154. The DIY column leaves out your time, a post and any replacement parts. The commercial units come with a warranty, support and, for Meterra, a sensor that reads under ice. For comparison, the Utah trial units came to $2,008 to $2,260 each over 3 years at 2009 prices.

Parts for one trough

USD, US915 band, as listed on each store page on Oct 23, 2026. $91.29 with the IP65 box. Shipping and tax not included.

A gateway, if you need one

One gateway covers every trough it can reach. Skip this if a public TTN gateway already reaches you.

Step by step

1. 1. Check for LoRaWAN coverage first

   Look for public gateways near your troughs on the TTN map and on TTN Mapper. If one reaches you, you can skip the gateway. If not, plan on a RAK7268V2 at the house or barn, with its antenna as high as you can get it.

   The Things Network gateway map, TTN Mapper

2. 2. Set up the network server

   The easy path is a free account on The Things Network (TTN). Its fair use policy allows 30 seconds of airtime per node per day and 10 downlinks, which is plenty for a reading every 15 to 30 minutes. If you'd rather own everything, run ChirpStack on the gateway or a small server.

   TTN fair use policy, ChirpStack (MIT)

3. 3. Flash the node

   Install the RAK nRF52 board support in the Arduino IDE and start from RAK's deep-sleep LoRaWAN example for the RAK4631. It sleeps, wakes on a timer, sends one packet and sleeps again. Register the device on TTN and paste in its keys for OTAA join.

   git clone https://github.com/RAKWireless/WisBlock.git
   # open examples/RAK4630/communications/LoRa/LoRaWAN/RAK4631-DeepSleep-LoRaWan
   # set your DevEUI, AppEUI and AppKey, pick US915, upload

   RAKWireless/WisBlock repo (MIT), RAK4631 deep-sleep LoRaWAN example, SX126x-Arduino library (MIT)

4. 4. Read the sensor

   Wire the A02YYUW to 3.3 V, ground and the board's serial RX. Each reading is 4 bytes: 0xFF, a high byte, a low byte and a checksum. Distance in millimeters is high × 256 + low. Power the sensor only while reading, then send the distance in a 2-byte payload.

   // frame: 0xFF H L SUM, SUM = (0xFF + H + L) & 0xFF
   uint16_t mm = (H << 8) | L;

   DFRobot A02YYUW (SEN0311), ESPHome A02YYUW docs (frame format)

5. 5. Turn distance into a water level

   Measure from the sensor face to the trough bottom once. Level is that number minus the reading. Do this in a TTN payload formatter or on your server, so you can recalibrate without opening the box.

   TTN webhooks

6. 6. Send alerts to your phone and email

   Point a TTN webhook at ntfy, the free open-source push service. With message templates, ntfy can set the priority from the level, so normal readings stay quiet and a low trough rings your phone. For email, send only the alarms through Node-RED, since ntfy's free tier allows 5 emails a day.

   https://ntfy.sh/<your-topic>?tpl=yes&m=Trough+{{.uplink_message.decoded_payload.level_cm}}+cm
   &p={{if lt .uplink_message.decoded_payload.level_cm 20.0}}5{{else}}1{{end}}

   ntfy message templating, ntfy email notifications, ntfy plans, Node-RED (Apache 2.0)

7. 7. Build the box and mount it

   The board, battery and plate go in the Unify enclosure, the sensor cable comes in through the gland, and the box straps to a post. Put the sensor arm where it points at open water away from the float valve, and mount everything out of reach of cattle.

   RAK Unify Enclosure IP65 100x75x38 Solar, RAK Unify pole mounting kit, SDSU Extension, water monitoring systems for livestock

8. 8. Run it next to your normal checks for a month

   Keep driving the route for a few weeks and compare what you see with what the node reports. Watch for spikes, missed uplinks and battery voltage on cloudy days. Utah's trial saw all three with commercial units.

   Heaton, USU Extension, rancher evaluation slides

The code is shortened. The firmware base and ChirpStack are MIT licensed, and ntfy and Node-RED are open source too, so you can run the whole thing on your own hardware.

What's hard

• Cold weather

  Consumer lithium cells shouldn't be charged below freezing, and the A02YYUW is rated only to -15°C. An ultrasonic sensor also reads the top of the ice, not the water under it. Meterra's submerged pressure sensor is built for that.

  How to help: Test a low-temperature charging cutoff or an LiFePO4 pack and share the circuit and winter data.

• Power on short winter days

  We haven't measured how long the 500 mAh cell lasts on the small lid panel. Utah's trial saw low batteries in cloudy weeks even on commercial units.

  How to help: Log battery voltage in every uplink and post a month of it with your reporting interval.

• Range and coverage

  LoRaWAN range depends on terrain and antenna height. A trough behind a ridge may never reach the house. Satellite units like Ranchbot and Meterra's satellite option exist for that reason.

  How to help: Map your coverage with TTN Mapper before buying, and share what worked on your ground.

• Cattle, splashing and false readings

  Cattle rub on posts and chew cables, and a sensor that sees the trough rim or a float valve gives bad numbers. Utah's trial logged data spikes and a failed sensor on commercial units.

  How to help: Share a bracket design that keeps the sensor out of reach and aimed at open water.

• Nobody reports field results for builds like this

  We found DIY trough sensors but no multi-month field data on this exact parts list.

  How to help: Run a node for a season and publish uptime, battery and accuracy.

Battery University BU-410, charging at low temperatures, DFRobot A02YYUW (SEN0311), Heaton, USU Extension, rancher evaluation slides, TTN Mapper

Research behind the numbers

Walker et al., Rangelands 43(2), 2021, Same paper, University of Arizona repository, DOI 10.1016/j.rala.2020.12.001, USU Extension, remote stock water monitoring, SDSU Extension, water monitoring systems for livestock