Multi-Depth Soil Sensing Node
A solar-assisted LoRaWAN soil probe measuring moisture and temperature at four depths, with a five-year field life.
- Client
- Bluente Agritech
- Sector
- Agritech
- Year
- 2023
- Duration
- 16 weeks
- Layers
- 4
- Board size
- 46 × 46 mm
- Placements
- 98
- IPC class
- Class 2
Stack-up: 1.0 mm FR-4, 1 oz, ENIG, conformal coated
The challenge
A five-year life on a single primary cell with solar assist, in a sealed housing, reporting four sensor depths every fifteen minutes over LoRaWAN. The client's existing node managed fourteen months.
Our approach
We audited every leakage path on the previous design and found 62 µA of the 78 µA sleep current came from three sources: a permanently biased sensor divider, an unnecessary pull-up on an I²C bus that was powered down, and a regulator with poor quiescent behaviour at light load. Sensors were switched through a load switch, the bus was properly isolated, and the regulator was replaced. The radio duty cycle was recalculated against the real reporting requirement, and unconfirmed uplinks were adopted with periodic confirmation rather than per-message acknowledgement.
The outcome
Sleep current fell from 78 µA to 3.1 µA. With the solar assist contributing, projected field life exceeds five years against the fourteen months previously achieved. Thirty units have now run two full seasons without a battery change.
Measured outcome
78 → 3.1µA
Sleep current
5+years
Projected field life
15min
Reporting interval
30
Units in field trial
Sleep current is found, not designed
Nobody sets out to leave a sensor divider biased. These paths accumulate, and the only way to remove them is to measure the board section by section with everything else powered down. The audit took two days and returned four years of field life.
Protocol choices are power choices
Confirmed LoRaWAN uplinks on every message double the radio energy and can triple it when the gateway is marginal. Periodic confirmation gives the same delivery assurance for a fraction of the budget.
Fourteen months of battery life became five years. The audit that found it took two days. We should have asked them a year earlier.
Have a board that needs designing?
Send us the constraints — schematic, mechanical envelope, volume, timeline. You will get a considered response from an engineer within one business day, not a brochure.
We reply within one business day, from an engineer.