Product description

Goal

The field MVP is the first useful outdoor version. It should be installable by a beekeeper with common tools and should avoid invasive electronics inside the colony. The product promise is simple: a DIY hive scale that streams weight, internal temperature, ambient humidity, battery status, and connectivity health into Gratheon.

This is the recommended public pilot scope.

Functionality

  • Measures hive weight for honey-flow, food-reserve, theft, storm, or handling events.
  • Measures internal temperature with a waterproof DS18B20 probe.
  • Measures ambient humidity and temperature with SHT31, SHTC3, or BME280 in a vented protected location.
  • Measures battery voltage or battery state so the web app can warn before telemetry stops.
  • Reports every 10-15 minutes by default.
  • Batches readings when WiFi is weak and retries with stable dedupeKey values.
  • Uses a simple weatherproof enclosure, cable glands, and external scale frame.
  • Uses phone or web setup instead of an outdoor LCD.

Field MVP architecture

flowchart LR
    loadcell[100-200 kg load cell or 4 x 50 kg bars] --> hx711[HX711]
    ds18b20[DS18B20 internal probe] --> esp32[ESP32 firmware]
    humidity[SHT31/SHTC3/BME280 ambient module] --> esp32
    battery[Battery voltage or fuel gauge] --> esp32
    hx711 --> esp32
    solar[Optional solar charger] --> battery
    esp32 --> provision[WiFi setup portal, hiveId, API token]
    esp32 -- "POST every 10-15 min, batch if offline" --> telemetry[telemetry-api /iot/v1/metrics]
    telemetry --> mysql[(time-series storage)]
    web[Gratheon web app] --> graphql[graphql-router]
    graphql --> telemetry
    web --> charts[Telemetry charts, alerts, hive comparison]

Electrical subsystem boundaries

The Field MVP should stop treating the enclosure as a breadboard box. Divide the hardware into serviceable subsystems.

Subsystem Inside enclosure Outside enclosure Connector or pass-through Recommendation
Weight HX711, ESP32 Load cell or scale frame Cable gland for MVP, M8/M12 later Keep low-level load-cell cable short and strain-relieved.
Internal temperature ESP32 pull-up resistor DS18B20 probe routed into hive PG7 cable gland or 3-pin waterproof connector Use 3-wire powered mode, not parasite power.
Ambient humidity SHT31/SHTC3/BME280 board Vented air pocket outside direct rain Internal cable, small protected vent, or remote pod Do not seal humidity sensor in the main box without air exchange.
Power Battery holder, charger, fuse, switch Optional solar panel Separate gland or 2-pin waterproof connector Keep solar/power wiring separate from load-cell signal cable.
Service/debug USB or UART header None during normal operation Internal header only Avoid an external USB hole in the enclosure for MVP.

Wiring rules for field reliability

  • Put a physical strain relief on every cable before it reaches solder joints or screw terminals.
  • Use drip loops so rainwater runs below the cable entry before reaching the enclosure.
  • Keep load-cell analog wires away from solar charger and boost-converter wiring.
  • Use ferrules or tinned wire ends in screw terminals only when the terminal type accepts them safely.
  • Label both ends of each cable. Outdoor debugging becomes slow when all black cables look identical.
  • Leave a small service loop inside the box so the lid can open without pulling wires.
  • Add a desiccant pack only as a short-term mitigation. The real fix is correct sealing, cable entry, and condensation path.

Suggested field pin allocation

Function Suggested ESP32 pin Interface Notes
HX711 DT GPIO16 Digital Keep from lab profile where possible.
HX711 SCK GPIO17 Digital Keep paired with DT.
DS18B20 data GPIO4 1-Wire 4.7 kOhm pull-up to 3.3 V.
SHT31/BME280 SDA GPIO21 I2C Keep cable short if the module is remote.
SHT31/BME280 SCL GPIO22 I2C Lower I2C speed if cable length causes errors.
Battery voltage GPIO34 or GPIO35 ADC Use resistor divider sized for low standby leakage.
Fuel gauge GPIO21/GPIO22 I2C MAX17048/LC709203 share I2C with humidity sensor.
Wake/service button Any safe GPIO Digital input Useful for on-site setup without opening logs.

Mechanical stack

The MVP should choose one of two load paths and document it with photos.

Option A - Single-point load cell

Use when a 100-200 kg single-point or platform-scale load cell can be mounted between two rigid plates.

  • Bottom plate sits on the hive stand.
  • Load cell is bolted according to its arrow/load direction.
  • Top plate supports the hive body.
  • Add mechanical stops so accidental overload does not permanently bend the load cell.
  • Add side guides that prevent the hive sliding sideways, but do not create a second load path.

Option B - Four bar load cells

Use when low-cost 50 kg bar cells are easier to source.

  • Put one cell near each corner.
  • Keep all four contact points at the same height.
  • Protect wires from crushing and rodents.
  • Calibrate the complete frame, not each cell in isolation.
  • Expect more corner-loading error than a good single-point design.

Sensor placement

Sensor Placement Avoid
Load cell Between rigid stand and hive base Off-axis force, rocking frame, water pooling around cable exit.
DS18B20 Under cover or near brood-area edge without blocking bees Loose cable inside colony, direct contact with wet surfaces, crushing under boxes.
Humidity/ambient module Shaded, vented pocket on enclosure underside or separate small pod Direct sun, rain splash, sealed box, condensation drip path.
Battery/fuel gauge Inside enclosure close to battery Hot roof surface, exposed terminals.
Solar panel Angled and cable-dripped before enclosure entry Cable pointing upward into gland, shading by hive roof.

Power budget workflow

Do not size solar only from panel marketing watts. Measure the device current in the MVP enclosure.

  1. Measure deep-sleep current.
  2. Measure wake current while reading sensors.
  3. Measure WiFi connect and HTTPS upload duration.
  4. Calculate daily energy for 10, 15, and 30 minute intervals.
  5. Choose a battery that survives several cloudy days without solar input.
  6. Add solar only after battery-only baseline is known.
  7. Report battery voltage or fuel-gauge percent in every telemetry batch.

Data sent by MVP

MVP firmware should send both beekeeper metrics and support metrics.

Type Fields Use
Beekeeper metrics weightKg, temperatureCelsius, humidityPercent Honey flow, food shortage, overheating, humidity risk.
Device metrics batteryVoltage, batteryPercent, rssi, firmwareVersion, resetReason Support, missing-data alerts, field reliability.
Calibration metadata calibration factor, tare timestamp, scale type Explains why two hive scales may differ.

API changes to consider after MVP

Not required for the first release, but useful for field reliability:

  • Add batteryVoltage, batteryPercent, solarVoltage, rssi, and firmwareVersion fields.
  • Add a device registry in the web app so a beekeeper can pair a physical device with a hive without manually copying hiveId.
  • Add a “last seen” and “missing telemetry” alert using the latest timestamp per device/hive.
  • Add calibration metadata: load-cell factor, tare date, and mechanical configuration.

Research references

Research backing has moved to 🧪 Research references. It links this Field MVP scope to Gratheon's Research section and explains why weight, temperature, humidity, battery health, and connectivity health stay ahead of heavier sensor modalities.

Exit criteria

  • Device survives rain-protected outdoor operation without water ingress.
  • Weight trend is useful enough to detect daily gain/loss and sudden movement.
  • Battery telemetry is visible or at least logged locally.
  • The device can run for a realistic pilot interval with the selected report cadence.
  • A beekeeper can install it without soldering inside the hive body.

Bill of materials

The detailed purchase list is in Phase 2 - Field MVP BOM. It adds an IP65 box, cable glands, battery, optional solar charger, humidity sensor, and better field wiring to the lab electronics.