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Plošná ryba Úl (PR-UL)

Device page · Flash firmware from the browser

A scale under a beehive that also measures temperature and humidity inside. It shows the hive weight, the daily gain (nectar flow) and fast weight changes that reveal a swarm. Sends data to Home Assistant over WiFi.

  • 4 load cells of 50 kg, up to 200 kg in total
  • HX711 converter
  • SHT40 in the hive for temperature and humidity
  • Calibration from Home Assistant, no programming
  • Powered with 5 V from any USB charger

What is in the box

  • Jádro board with the HX711 head in an enclosure with a seal ring
  • 4 half-bridge load cells of 50 kg, soldered to the HX711 at the factory and led into the enclosure through a cable gland
  • SHT40 sensor on a Qwiic cable, led into the enclosure through a cable gland
  • 5 V power cable led through a cable gland, ending in a USB-A plug for any USB charger
  • 4 printed feet: white corner with a cup and black base, the load cell goes between them
  • Wood screws for the bases and the electronics enclosure
  • Card with a link to this guide

You do not solder or thread anything. The USB charger is not included, any common one will do.

The default feet are for a stiff wooden hive floor. For a polystyrene or plastic floor there is a variant with corners for two wooden beams 45 x 45 x 500 mm. Buy the beams (pressure treated or larch) and 8 wood screws 4 mm for them at a DIY store, they are not included.

Installation

1. Set up the feet

Each foot is a black base on the ground, a load cell and a white corner with a cup that takes the corner of the hive floor. No beam is needed, the wooden floor carries the hive between the feet.

  1. Place the bases on a firm, level surface (a stand, paving slabs) in a rectangle matching the hive floor and screw them down, each has 4 screw holes. Level the surface, a tilted scale measures less accurately.
  2. Put one load cell into the pocket under each corner, raised centre facing down, and lead the cable through the cut-out on the side of the corner.
  3. Stand the corners on the bases. A corner should touch its base only through the pad under the load cell centre, never the rim of the base.
  4. Do not put the hive on yet, set up WiFi and calibrate first. Then lower the hive so the floor corners sit in the cups. You can fix each corner to the side of the floor with a wood screw.
  5. Keep leaves, snow and grass from getting under the corners and around the bases, only the load cells may carry the weight.

Polystyrene or plastic floor: a soft floor would bend at the feet, so two wooden beams 45 x 45 x 500 mm carry it. The corners of this variant have a channel for the beam instead of a cup. Prepare the bases and load cells the same way, push the beams into the corner channels up to the stop and fix them with 4 mm wood screws (2 per corner). Put the hive on the beams only after calibration.

2. Enclosure, sensor and power

  • Screw the enclosure with two wood screws through the keyhole slots to the stand, a beam or the hive floor, out of direct rain and ideally in the shade, glands facing down.
  • Put the SHT40 sensor into the hive, ideally above the crown board, out of direct contact with the bees (they would seal it with propolis).
  • Plug the USB-A plug into a USB charger. Keep the charger in a dry place. Without power at the apiary, a solar panel with a battery and a USB 5 V output does the job.

For repairs: the wiring diagram of the load cells to the HX711 is in hardware/heads/ul. Useful when you replace a damaged load cell.

Enclosure

To keep water out, the enclosure has no external USB-C port and no access to the buttons. The top face has no holes, the lid is held by two screws on the underside. The status LED shines through a thin spot in the lid: it is on while the device is not connected to WiFi (waiting for setup) and off in normal operation. USB-C and the BOOT and RESET buttons are reachable after loosening both screws and taking the lid off.

Connecting to WiFi

Best set up WiFi at home, before you close the enclosure and take it to the hive. Take the lid off (two screws on the underside) and pick one way:

  • From the browser over USB: open https://plosnaryba.cz/firmware in Chrome or Edge, connect the board with a USB-C cable, click Connect and enter your WiFi name and password (Improv).
  • Over Bluetooth in Home Assistant: if HA has Bluetooth (an adapter or an ESPHome Bluetooth proxy), it offers the new device for WiFi setup. Enter the details and confirm the pairing by pressing the BOOT button on the board. Without the BOOT press the device does not accept WiFi credentials.

The device has no fallback WiFi network and no default password. 2.4 GHz only. Apiaries are often far from the house, check the signal with your phone first.

Adding to Home Assistant

  1. Settings, Devices and services. The ESPHome device Plošná ryba Úl is listed as discovered. Click Add.
  2. Confirm. If HA offers to set an encryption key, accept it.
  3. Assign an area (for example Apiary). Entities appear on their own.

Calibration

Done once after assembly. The values are stored in the device and survive restarts and updates.

  1. The feet without the hive (with the beams, if you use them). Wait about 30 s for the value to settle and press Tare. The weight jumps to 0.
  2. Lay a board or the empty hive floor across the corners and put a known weight on it, ideally 10 to 30 kg (a water canister, a bag of cement). With the beam variant put the weight straight on the beams. The heavier, the more accurate.
  3. Enter the weight of the load plus the board or floor in kg into Known weight, check both on a bathroom scale.
  4. Wait 30 s and press Calibrate. The weight should now show the known weight.
  5. Remove the weight and the board, the reading returns to 0. Put the hive on.

Check: add another known weight and compare. Less than 1 % difference is a good result. Temperature affects load cells, during a day the weight may drift by tens of grams.

Do not tare with the hive on the scale, otherwise it only shows the change since the tare, not the hive weight.

Daily gain

  • Gain today: weight now minus the weight at midnight.
  • Gain yesterday: change over the whole previous day, calculated at midnight. If the device was off at midnight, yesterday's gain is unknown.
  • Change in 15 minutes: difference against the weight 15 minutes ago. A swarm takes 1.5 to 3 kg within minutes, here you see it immediately.

The device takes the time from Home Assistant, or from the internet (SNTP) when HA is not running.

Entities

Home Assistant builds the entity ID from the device name and the entity name, typically sensor.plosna_ryba_ul_weight. The table lists the suffix after the device name (English firmware build).

Type Suffix Meaning Unit
sensor weight weight on the scale kg
sensor gain_today change since midnight kg
sensor gain_yesterday change over the previous day kg
sensor change_in_15_minutes change over the last 15 minutes kg
sensor hive_temperature temperature from SHT40 °C
sensor hive_humidity relative humidity from SHT40 %
sensor hx711_raw_value raw converter value (diagnostic, hidden)
button tare sets zero
button calibrate calculates the scale from the known weight
number known_weight weight of the calibration load kg
sensor, binary_sensor battery_voltage, battery, charging come from the shared Jádro base, Úl has no battery and the values are meaningless
sensor wifi_signal signal strength dBm
sensor uptime time since start s
text_sensor firmware_version, ip_address diagnostics
button restart restart
light status_led status LED
binary_sensor boot_button BOOT button
switch head_power HX711 power (hidden)

Automations

Swarm alert. Runs only during the day, when bees swarm.

automation:
  - alias: "Hive: possible swarm"
    triggers:
      - trigger: numeric_state
        entity_id: sensor.plosna_ryba_ul_change_in_15_minutes
        below: -1.0
    conditions:
      - condition: time
        after: "09:00:00"
        before: "18:00:00"
    actions:
      - action: notify.mobile_app_phone
        data:
          title: "Hive: sudden weight drop"
          message: >
            {{ states('sensor.plosna_ryba_ul_change_in_15_minutes') | float | abs }} kg lost
            in 15 minutes. This may be a swarm.

Adjust the -1.0 kg threshold to the strength of your colonies. Removing a super during an inspection causes the same drop, keep that in mind.

Evening nectar flow summary:

automation:
  - alias: "Hive: daily gain"
    triggers:
      - trigger: time
        at: "21:00:00"
    actions:
      - action: notify.mobile_app_phone
        data:
          message: >
            Gain today: {{ states('sensor.plosna_ryba_ul_gain_today') }} kg,
            inside the hive {{ states('sensor.plosna_ryba_ul_hive_temperature') }} °C.

Troubleshooting

Problem What to try
Weight is always 0 or nonsense Do Tare and Calibrate. Without calibration only a rough estimate applies.
Calibration does nothing The difference from tare is too small: no load, too light, or Tare was not done empty. The device log shows the reason.
Weight goes down when I add load Fine, calibration handles it. Just do Tare and Calibrate again.
Weight depends on where the load stands A load cell does not sit properly in its corner pocket, a corner touches the rim of its base, or something other than the load cells carries weight (leaves, grass, the ground).
Weight slowly drifts Temperature, moisture in the joints, or the ground under the bases is settling. Some drift in the first week is normal.
Hive temperature missing Take the lid off and check the Qwiic cable. SHT40 has address 0x44, the device log lists the I2C bus.
Humidity 100 % Water condensed on the sensor. Move it higher above the brood where the air is drier.

Power

Úl has no battery and needs permanent 5 V power, because swarm detection needs continuous measurement. Any USB charger will do. If there is no power at the apiary, use a solar panel with a battery and a USB 5 V output.

Safety

  • No mains voltage: the device runs on 5 V only. Keep the 230 V USB charger in a dry place and run only the 5 V cable to the hive. Never bring 230 V to the hive without residual current protection and outdoor-rated enclosures.
  • Outdoors: protect the enclosure from direct rain and do not drill extra holes into it. Condensation inside the enclosure ruins connections over time. The enclosure and the feet are PETG, which becomes brittle in direct sun over time, so keep the enclosure in the shade.
  • Bees: during assembly and calibration work as you would at any hive, with protective gear.
  • The scale is not a certified measuring instrument, it is for guidance.