LoRa Sensor Node
Two-node raw LoRa P2P link for environmental sensing using Heltec WiFi LoRa 32 V3 boards (ESP32-S3 + SX1262). Not LoRaWAN – direct radio-to-radio communication with SPI-level debugging.
Hardware
| Component | Qty | Description |
|---|---|---|
| Heltec WiFi LoRa 32 V3 | 2 | ESP32-S3 + SX1262 + OLED, onboard u.FL |
| DHT11 | 1 | Temperature/humidity sensor |
| Logic analyzer | 1 | 24MHz 8CH for SPI captures |
Radio Configuration
| Parameter | Value |
|---|---|
| Frequency | 915 MHz (US ISM) |
| Spreading Factor | SF9 |
| Bandwidth | 125 kHz |
| Coding Rate | 4/7 |
| TX Power | 14 dBm |
Packet format: T:23.4 H:61.2 N:0042 – plain ASCII with sequence number for tracking packet loss.
LoRa Physical Layer
LoRa uses chirp spread spectrum (CSS). Higher spreading factor = longer range but lower data rate:
| SF | Data Rate | Sensitivity | Range (LoS) |
|---|---|---|---|
| SF7 | ~5.5 kbps | -123 dBm | 2-3 km |
| SF9 | ~1.8 kbps | -129 dBm | 5-7 km |
| SF12 | ~250 bps | -137 dBm | 10-15 km |
SF9 is the default – good balance of range and airtime for sensor reporting.
Milestones
- Environment setup and board validation
- TX firmware – periodic sensor read + LoRa transmit
- RX firmware – receive, parse, display on OLED
- SPI captures – logic analyzer traces of SX1262 register writes
- Light sleep between transmissions
- Current measurement and power profiling
- Range testing outdoors