Embedded Firmware Engineer — Nordic nRF9151 / Zephyr / NB-IoT Environmental Monitoring Device

About the project We build satellite and cellular IoT environmental monitoring systems deployed with Australian local government customers. This engagement is to develop production firmware for a flood monitoring device built on the Nordic nRF9151 DK. The device is already deployed commercially, this is contracted delivery work, not a hobby prototype. Firmware development and bench-level integration. We ship hardware (DK, sensors, antennas, SIMs) to you and provide platform access. You provide wiring documentation, sensor interface recommendations, and assembly guidance for our production builds as part of the deliverables. Hardware platform Nordic nRF9151 SMA DK (nRF Connect SDK / Zephyr) MaxBotix MB7388 ultrasonic distance sensor (pulse-width output) Rain gauge integration (UART/interrupt — model confirmed at kickoff) OmniPreSense OPS243-C radar (UART, power-managed) — later phase Solar/battery power, battery voltage telemetry required Phase 1 scope (this contract) Milestone 0 — Qualification build (small fixed price, 1 week) Project setup on nRF Connect SDK MB7388 integrated and reporting distance readings every 4 hours Telemetry delivered over NB-IoT (Optus, physical SIM) via MQTT/TLS into our ThingsBoard instance Acceptance: live demonstration of readings arriving in ThingsBoard Milestone 1 — Full sensor and connectivity build (fixed price, 3 weeks) Rain gauge integration with rain-detection interrupt Routine 4-hourly sampling; configurable event-mode framework Persistent flash-backed telemetry queue (store on link loss, forward on recovery) Battery voltage telemetry Registration timeout, retry, and recovery handling Initial power profiling Source code and technical documentation Wiring documentation and assembly guidance for production replication Acceptance: all sensors reporting on schedule into ThingsBoard, queue behaviour demonstrated by forced link loss, documentation delivered Later phases (scoped separately, same engineer preferred) Satellite NTN integration (LEO NB-NTN, dual-bearer switching with terrestrial fallback, UDP/CoAP, compact binary payloads) Event-mode fast sampling and near-real-time alert delivery MCUboot secure FOTA with image validation and rollback Watchdog, fault logging, duty-cycle optimisation Candidates with prior 3GPP NTN / satellite NB-IoT experience: say so — it strongly influences later-phase selection. Requirements Demonstrated commercial delivery on Nordic nRF91 series with nRF Connect SDK and Zephyr (link to shipped work, repos, or verifiable contract references) LTE-M/NB-IoT modem experience (AT command handling, link management, power states) MQTT/TLS integration experience Comfortable with milestone acceptance by live demonstration, not code hand-off alone Written progress updates every 2–3 days Working terms Repository under our GitHub organisation from day one; no code held solely on personal machines All code, keys, and credentials assigned to our IP-holding entity on payment (standard IP assignment terms in contract) Payment released on demonstrated acceptance per milestone Out-of-scope changes quoted before implementation Screening questions Link one nRF91/Zephyr project you delivered commercially. What was your specific contribution? Describe how you would implement a flash-backed telemetry queue on Zephyr that survives reset and delivers on link recovery. What is your approach to power profiling a solar/battery NB-IoT device with a 4-hour reporting cycle? Your fixed price and timeline for Milestone 0 as scoped above? Any hands-on NTN / satellite NB-IoT experience? Describe briefly. To apply: answer the five questions. Applications without them won't be reviewed. Start your reply with the word "Ultrasonic" so we know you read the full post.