Low-Power LoRa Sensor Node
A solar-trickle sensor node that reports over LoRa and keeps running for months on a single coin cell as backup.
Overview
The power budget drives every decision here. The MCU spends almost all its life in a deep sleep state, waking briefly on a timer to sample a sensor, and waking the LoRa radio even more rarely to transmit — LoRa's long range comes at the cost of relatively high transmit current, so airtime is the thing to ration hardest.
A small solar cell trickle-charges a supercap or tops up a CR2032 through an energy-harvesting front end during the day; at night or in low light, the node lives off that stored charge. Because LoRa is a long-range, low-bandwidth link, one small antenna and a modest solar cell are enough to keep a remote sensor reporting for months without anyone visiting it.
Block Diagram
Key Components
- Low-power MCU with a deep-sleep current in the low microamps
- LoRa transceiver module with a matched antenna
- Small solar cell sized for the local light conditions
- Energy-harvesting / charge-management IC
- CR2032 coin cell or supercap as backup storage
- Ultra-low-quiescent-current LDO or buck regulator
- Environmental sensor (temperature/humidity, or whatever the deployment needs)
Bill of Materials
| Ref | Part / Value | Rating | Package |
|---|---|---|---|
| U1 | STM32L011F4 — ultra-low-power MCU | 1.65–3.6V | QFN-20 |
| U2 | SX1276 — LoRa transceiver | 868/915MHz, +20dBm | QFN-48 |
| U3 | BQ25570 — solar energy harvester/charger | 100mV–5.5V input | QFN-20 |
| U4 | SHT31-D — temperature/humidity sensor | I2C, 2.4–5.5V | DFN-8 |
| U5 | TPS7A02 — ultra-low-Iq LDO, 3.3V | 25nA quiescent | SOT-23 |
| BT1 | CR2032 coin cell | 3V, 220mAh | ⌀20mm |
| PV1 | Small solar cell | 5.5V, 40mA | 40×40mm |
| L1, C1, C2 | RF matching network (2.7nH / 2.2pF) | for 868/915MHz | 0402 |
Build Requirements
- Careful RF layout and antenna matching — a poorly matched antenna quietly kills range and burns extra transmit power
- Low-power firmware discipline: sleep modes, watchdog-timed wake-ups, and duty-cycled radio use
- A LoRa gateway (or access to one) to actually receive the uplinks
- Basic understanding of regional LoRa duty-cycle / airtime regulations