Sample Project: Wireless Environmental Sensor Node

• Measure temperature (±0.2 °C), relative humidity (±2 %RH) and ambient light once per minute.
• Report over BLE advertising to existing gateways; no pairing or app required.
• Three-year battery life from a single CR2477 coin cell.
• Enclosure limited the board to 38 × 30 mm with a fixed mounting-hole pattern.
• Target BOM cost under a defined ceiling at 1k-unit volume; parts chosen for multi-source availability.

A single nRF52832 handles both application and radio. The sensors (SHT40 for temperature/humidity, VEML7700 for light) sit on a dedicated I²C bus behind a load switch so the whole sensor cluster can be fully de-powered between measurements. A TPS62840 buck converter steps the cell voltage down to 1.8 V for the digital domain; the radio runs in its DC/DC mode to cut TX current. Firmware wakes on an RTC tick, powers the sensors, samples, encodes the readings into a manufacturer-specific BLE advertisement and returns to system-off-like sleep.

• Coin-cell power path with bulk storage capacitance sized for the 8 mA radio TX pulses, keeping cell voltage sag within the datasheet pulse-load limits.
• Load-switched sensor domain so sensor sleep current does not count against the battery budget.
• SHT40 placed on a slot-isolated board region to decouple it from MCU self-heating.
• 2.4 GHz chip antenna with a ground keep-out and a π matching network placed for post-assembly tuning.
• Tag-Connect footprint instead of a debug header to save board area and BOM cost.

• Zephyr-based application with a single measurement state machine; no RTOS threads beyond the BLE stack's own.
• Manufacturer-specific advertising payload with sequence counter, battery voltage and sensor readings.
• Calibration offsets stored in a settings partition, writable over a factory-only UART protocol.
• MCUboot bootloader with dual-slot layout; OTA transport intentionally omitted to preserve the power budget, updates applied over the factory UART.
• Watchdog and brown-out handling with a boot-reason counter reported in the advertisement for fleet diagnostics.

• Power-rail and short checks on every rail before first power-on of each revision.
• Current profiling of the full wake/measure/advertise cycle with the Power Profiler Kit, compared against the battery-life spreadsheet model.
• Sensor accuracy spot-checks against a calibrated reference in a temperature chamber.
• BLE range walk-test in an occupied office floor against the gateway placement plan.
• One-week soak of ten units logging advertisement loss and reset counters.

Revision B passed all bench and soak tests; the measured energy-per-cycle figures support the three-year battery-life target with roughly 20 % margin in the model. A pilot batch was assembled and handed over with the full manufacturing package. (Fictional example outcome, written to show the level of honest detail to aim for.)

• KiCad schematic and layout source files
• Gerber, drill and pick-and-place files, assembly drawings
• BOM with alternates for all passives and the load switch
• Firmware source, factory-UART calibration tool and flashing scripts
• Bring-up guide and test report