Ultra-low-power IoT water meter: injection-moulded enclosure, exo-modules, and BLE provisioning in the app.
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
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
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)
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
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
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
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
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
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
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
Main path (acceptance)
- 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 · CoAP telemetry
The radio module sends CoAP PUT to /telemetry. The ingestion service responds with success (2.01) and status OK.
- 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 · 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
CoAP PUT /device-config with device UUID — returns multipliers and schedule; the next telemetry packet uses that configuration.
With the calibration flag set, multipliers and optionally historical rows are updated in the backend; the portal shows corrected consumption.
A raw value on the leak sensor triggers an async alert path (rate-limited) in addition to normal event storage.
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
Technologies
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