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Solvetronix
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IOT-007 Metrology · OEM IoT · ULP · Exo modules · App

Ultra-low-power IoT water meter: injection-moulded enclosure, exo-modules, and BLE provisioning in the app.

ULP
STM32L4 · Stop2
5 exo
Wi‑Fi · LoRa · NB · RS-232 · BLE
Mould
tooling CN
App
BLE advertising

Situation

A smart-metering OEM needed a next-generation water meter: Class C accuracy, magnetic tamper protection, and remote readout for residential and professional sites (housing operators, utilities).

Typical all-in-one meters force seal breaking when the radio standard or power scheme changes — expensive service and re-approval. The target was a modular ULP platform plus series-ready enclosure and connectivity.

Solvetronix covered the full path: coordinate injection-moulded housings with partners in China, develop the base board and exo-modules (Wi‑Fi, NB‑IoT, LoRa, RS-232), BLE firmware on the radio chip, and BLE advertising reception in the mobile app.

Approach

1
1 Specification

ULP architecture and metrology

  • Class C, pulse and display requirements, ≥ 12 year battery target
  • STM32L4 line: 32.768 kHz RTC, Stop2 sleep profiles, minimal active time
  • Anti-magnetic detection and tamper flags in firmware
2
2 Tooling

Enclosure: injection moulding (China)

  • Coordination with injection-mould partners in China for series housings
  • Mould tooling, material, and tolerances for metrology and exo interface
  • Enclosure ↔ electronics alignment (base PCB, exo slot, sealing, assembly)
3
3 PCB

Modular hardware (base + MultiCom)

  • Base board: meter interface, SPI flash, backlit LCD
  • B2B connector for exo-module — radio and power off the sealed core
  • MultiCom bus: plug in, detect, commission
4
4 Power

Dual power without measurement gap

  • Built-in battery plus swappable exo energy module
  • Seamless supply switch during operation
  • Architecture suitable for later IP protection — no opening the metrology enclosure
5
5 Embedded

ULP firmware (metrology core)

  • Archiving, events (magnet, leak suspicion, low battery, enclosure)
  • OTA and diagnostics only via exo-module — core firmware protected
  • Display: consumption, battery, link quality on one screen
6
6 Exo design

Exo-modules: Wi‑Fi, NB‑IoT, LoRa, RS-232

  • Dedicated exo PCBs per connectivity — unified MultiCom interface to the ULP core
  • Wi‑Fi and NB‑IoT for IP/cellular telemetry; LoRa for LPWAN; RS-232 for building and SCADA wiring
  • Firmware bring-up, protocol bridge to the meter core, CoAP/MQTT to the cloud platform
7
7 BLE · App

BLE chip firmware and mobile app

  • Firmware for the BLE chip on the exo-module (advertising, GATT services per product schema)
  • Mobile app: receive and parse BLE advertising packets for discovery and first-time setup
  • Provisioning path alongside Wi‑Fi SoftAP — field devices discoverable without display interaction
8
8 Acceptance

Cloud and certification

  • Housing-operator / utility integration, real-time events (MQTT)
  • EMC pre-checks and documentation for test-lab iteration
  • Modular product platform: enclosure, core, exo line, app

How the solution works

Injection-moulded housing (tooling · CN)
↓
ULP metrology core (sealed) (STM32L4 · Class C)
↓
MultiCom → exo-module (Wi‑Fi · NB‑IoT · LoRa · RS-232)
↓
BLE chip + advertising (firmware · mobile app)
↓
Cloud / MQTT (telemetry · events)

The platform was accepted as a full data path, not only as a hardware line: one pulse at the meter shows up in the operator web portal — without manual import. Below is the public acceptance path (anonymized, no client names).

Data path

Pulse / channel value (meter MCU · ULP core)
↓
Binary payload → radio module (UART · base64)
↓
CoAP PUT /telemetry (UDP · port 5683)
↓
Ingestion + PostgreSQL (parse · transaction · events)
↓
Message queue (async · downstream)
↓
Operator portal (REST · chart · events)

Main path (acceptance)

  1. 1 · Measurement on device

    The metering MCU captures channel values (volume, voltage, states), encodes a binary payload, and hands it to the radio exo-module.

  2. 2 · CoAP telemetry

    The radio module sends CoAP PUT to /telemetry. The ingestion service responds with success (2.01) and status OK.

  3. 3 · Persistence and bus

    After parsing, values land in the device database (calculated reading, raw value, timestamp). Messages are published to the message queue in parallel.

  4. 4 · Visibility in portal

    After sign-in, the device overview shows online status; the trend chart gets a new point aligned with the field timestamp (within staging SLA tolerance).

Additional accepted paths

a
Config before telemetry

CoAP PUT /device-config with device UUID — returns multipliers and schedule; the next telemetry packet uses that configuration.

b
Calibration after flow test

With the calibration flag set, multipliers and optionally historical rows are updated in the backend; the portal shows corrected consumption.

c
Leak channel

A raw value on the leak sensor triggers an async alert path (rate-limited) in addition to normal event storage.

d
Fault tolerance

Invalid token or corrupted payload → rejected CoAP request; DB stays consistent. Queue outage does not block the CoAP OK response when the DB transaction succeeds.

Acceptance checklist (staging)

  • CoAP /telemetry → OK response
  • New row in device event store
  • Queue message with correct device ID
  • Device summary API reflects the controller
  • New point visible on portal chart

Results

Modular IoT platform — sealed ULP core, field-swappable exo-modules
Injection-moulded housing coordinated with China partners — tooling through assembly alignment
Exo-modules for Wi‑Fi, NB‑IoT, LoRa, and RS-232 developed as a dedicated PCB line
BLE firmware on the radio chip plus app support for advertising reception (provisioning)
Ultra-low-power on STM32L4 with ≥ 12 year battery target in the product concept
Cloud telemetry and EMC preparation for the certification cycle

Technologies

Ultra-low power (ULP)STM32L4Injection moulding (CN)MultiCom busExo-modulesWi‑Fi / NB‑IoT / LoRa / RS-232BLE chip firmwareBLE advertisingMobile appCoAP / MQTTOTAEMC pre-checks

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