Bill of materials
Description
The lab BOM is for a bench prototype. It proves the sensor chain, firmware, telemetry API contract, and calibration workflow before any weatherproofing or mechanical frame work starts.
Functionality covered
- ESP32 reads one load cell through HX711.
- ESP32 reads one waterproof DS18B20 temperature probe.
- Firmware sends telemetry to
/iot/v1/metricsevery 30-60 seconds. - Device is powered over USB.
- Setup and debugging happen over serial logs.
Bill of materials
| Tier | Component | Example part | Qty | Rough cost | Purchase links | Notes |
|---|---|---|---|---|---|---|
| Required | Microcontroller | ESP32 DevKit / ESP32-WROOM-32 board | 1 | €4-10 | Existing AliExpress ESP32, Espressif ESP32-DevKitC at DigiKey, ESP32-DevKitC at Mouser | Use a common USB-powered dev board for simplest onboarding. |
| Required | Weight ADC | HX711 load-cell amplifier breakout | 1 | €1-8 | SparkFun HX711 breakout, Adafruit HX711 breakout, Generic HX711 on AliExpress | SparkFun/Adafruit are easier for docs; AliExpress is cheaper. |
| Required | Test load cell | 1 kg to 50 kg bar load cell | 1 | €3-10 | Existing 50 kg bar load-cell listing, SparkFun load cell category, Amazon load-cell kits | Lab can use a small cell before the full hive scale frame exists. |
| Required | Waterproof temperature sensor | DS18B20 probe | 1 | €2-10 | Existing AliExpress DS18B20, Adafruit waterproof DS18B20, Amazon DS18B20 search | Use waterproof version even in lab so field wiring is similar. |
| Required | Prototyping wiring | Jumper wires, breadboard, screw terminals | 1 set | €3-8 | Adafruit jumper wires, Amazon jumper-wire search, local electronics shop | Screw terminals reduce intermittent sensor wiring. |
| Required | USB power/data | USB cable and laptop/USB charger | 1 | €0-5 | Local electronics shop, existing cable | Keep power simple in lab. |
| Optional | Pull-up resistor kit | 4.7 kOhm resistor for DS18B20 data line | 1 | <€1 | Amazon resistor kit search, local electronics shop | Needed for reliable 1-Wire communication if not built into probe board. |
| Optional | Bench display | LCD1602 I2C display | 1 | €2-6 | Existing LCD1602 listing, Amazon LCD1602 I2C search | Debug only; do not include in outdoor MVP by default. |
Connection accessories
These small items are worth buying early because they reduce false debugging work:
- 2-pin and 3-pin screw-terminal blocks for DS18B20 and power.
- 4-pin screw-terminal block for load-cell wires.
- Heat-shrink labels or masking-tape flags for
E+,E-,A+,A-,DATA,3V3, andGND. - A known calibration weight. A dumbbell or water container is acceptable if its mass is measured once on a trusted scale.
Exit criteria
- Weight reading is stable enough to detect known test weights.
- Temperature readings are visible in serial logs.
- A telemetry payload is accepted by
telemetry-api. - Gratheon UI can show the submitted history.
- Calibration factor can be stored and reused after restart.