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Case Study — Wireless Sensor Node: Concept to Certified Product in 14 Weeks
Background
A client approached us with a requirement for a battery-powered wireless sensor node for industrial environment monitoring.
- BLE 5.0 connectivity
- 2-year battery life on AA cells
- IP67 enclosure
- ±0.5°C temperature accuracy
- CE/FCC certification
The Challenge
The 2-year battery life target with frequent BLE advertising was aggressive. Initial estimates using standard BLE advertising intervals showed an expected battery life of under 8 months. A fundamental architecture change was needed.
Our Approach
Hardware
We selected the Nordic nRF52840 for its best-in-class low-power BLE performance and hardware crypto support. A precision TI temperature sensor with <0.1°C error was selected with a 1.8V interface to reduce leakage current. Custom low-dropout power sequencing ensured the MCU and sensor were fully powered down between measurements.
Firmware
Advertising interval was extended to 10 seconds in idle mode, with connection-interval negotiation reducing active radio-on time to under 3ms per event. System current in deep sleep: 2.3µA.
Mechanical
The enclosure was designed with a captive O-ring seal and sealed magnetic reed switch for zero-penetration activation. PCB was fully conformally coated.
Results
- Measured battery life: 26 months (exceeds target)
- BLE range: 85m line-of-sight (exceeds 40m requirement)
- CE Mark and FCC ID obtained in first submission
- Unit cost at 1000 units: within 8% of target
Lesson Learned
Power architecture decisions need to happen at schematic stage, not after PCB layout. The firmware-hardware co-design on power gating was the difference between meeting the spec and missing it entirely.