Week 10: LoRaWAN Sensor Network with STM32WL55

Project: LoRaWAN Sensor Network - Native STM32WL integrated radio Hardware: 2x NUCLEO-WL55JC1 + RAK7268V2 Gateway Network Server: RAK Built-in LoRa Server (AU915) Status: ✅ COMPLETE - Both nodes operational, Grafana dashboard live

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System Overview

Week 10 implements a production LoRaWAN sensor network using STM32WL55 microcontrollers with native SubGHz radio. The system includes a complete data pipeline from sensors to Grafana visualization.

Architecture

┌─────────────────────────────────────────────────────────────────────────┐
│                     LORAWAN SENSOR NETWORK                               │
├─────────────────────────────────────────────────────────────────────────┤
│                                                                          │
│  ┌──────────────────────┐         ┌──────────────────────┐              │
│  │ LoRa-1               │         │ LoRa-2               │              │
│  │ STM32WL55JC1         │         │ STM32WL55JC1         │              │
│  │ SHT41 (Temp/Hum)     │         │ BME680 (Env Sensor)  │              │
│  │ SSD1306 OLED 128x32  │         │ SH1106 OLED 128x64   │              │
│  │ DevEUI: 23ce1b...    │         │ DevEUI: 24ce1b...    │              │
│  └──────────┬───────────┘         └──────────┬───────────┘              │
│             │                                 │                          │
│             │         LoRaWAN AU915           │                          │
│             │        (915.2-916.6 MHz)        │                          │
│             └────────────────┬────────────────┘                          │
│                              │                                           │
│                              ▼                                           │
│                    ┌──────────────────────┐                             │
│                    │ RAK7268V2 Gateway    │                             │
│                    │ Built-in LoRa Server │                             │
│                    │ MQTT: 10.10.10.254   │                             │
│                    │ Application: "TOT"   │                             │
│                    └──────────┬───────────┘                             │
│                               │                                          │
│                               │ MQTT (TCP :1883)                        │
│                               ▼                                          │
│  ┌─────────────────────────────────────────────────────────────────┐   │
│  │                     Docker Services                              │   │
│  │  ┌─────────────────┐  ┌─────────────┐  ┌─────────────────────┐  │   │
│  │  │ wk10-mqtt-bridge│─▶│ wk7-influxdb│─▶│ wk7-grafana         │  │   │
│  │  │ Python decoder  │  │ Time-series │  │ Dashboard           │  │   │
│  │  │                 │  │ :8086       │  │ :3000               │  │   │
│  │  └─────────────────┘  └─────────────┘  └─────────────────────┘  │   │
│  └─────────────────────────────────────────────────────────────────┘   │
│                                                                          │
└─────────────────────────────────────────────────────────────────────────┘

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Hardware Configuration

LoRa-1 - SHT41 Temperature/Humidity Sensor ✅ OPERATIONAL

Component	Specification
MCU	STM32WL55JC1 (Probe: 003E00463234510A33353533)
Sensor	SHT41 (I2C 0x44) - High-precision temp/humidity
Display	SSD1306 OLED 128x32 (I2C 0x3C)
I2C Bus	I2C2: PA12 (SCL), PA11 (SDA)
Radio	Integrated SubGHz SX126x
DevEUI	23ce1bfeff091fac
Payload	4 bytes (temp + humidity)

Current Readings: ~31°C, 58% RH Uplink Interval: ~30 seconds

LoRa-2 - BME680 Environmental Sensor ✅ OPERATIONAL

Component	Specification
MCU	STM32WL55JC1 (Probe: 0026003A3234510A33353533)
Sensor	BME680 (I2C 0x76) - Temp/Hum/Pressure/Gas
Display	SH1106 OLED 128x64 (I2C 0x3C)
I2C Bus	I2C2: PA12 (SCL), PA11 (SDA)
Radio	Integrated SubGHz SX126x
DevEUI	24ce1bfeff091fac
Payload	12 bytes (temp + humidity + pressure + gas + padding)

Current Readings: ~28°C, 60% RH, 1020 hPa, 134 kOhm gas resistance Uplink Interval: ~30 seconds

Gateway - RAK7268V2 WisGate Edge Lite 2 ✅ OPERATIONAL

Parameter	Value
Gateway EUI	ac1f09fffe1bce23
IP Address	10.10.10.254
Region	AU915 Sub-band 2 (915.2-916.6 MHz)
Network Server	Built-in LoRa Server (NOT ChirpStack)
MQTT Broker	10.10.10.254:1883 (no auth)
Application	"TOT"

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Data Pipeline

End-to-End Flow

Sensor → STM32WL55 → LoRaWAN → RAK Gateway → MQTT → Python Bridge → InfluxDB → Grafana

Components

1. MQTT Bridge (mqtt_to_influx.py)

   • Subscribes to gateway MQTT (10.10.10.254:1883)
   • Decodes Base64 LoRaWAN payloads
   • Writes to InfluxDB with tags (node, sensor, dev_eui)

2. InfluxDB (wk7-influxdb container)

   • Bucket: lorawan
   • Measurement: lorawan_sensor
   • Fields: temperature, humidity, pressure, gas_resistance, rssi, snr

3. Grafana Dashboard (wk7-grafana container)

   • URL: http://localhost:3000/d/lorawan-sensors/lorawan-sensor-network
   • 10 panels: Temperature, Humidity, Pressure, Gas, RSSI, SNR, Stats

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Building and Flashing

Prerequisites

# Install probe-rs
curl --proto '=https' --tlsv1.2 -LsSf \
  https://github.com/probe-rs/probe-rs/releases/latest/download/probe-rs-tools-installer.sh | sh

# Add Rust embedded target
rustup target add thumbv7em-none-eabihf

Build and Flash

LoRa-1:

cd firmware/lora-1
cargo run --release

LoRa-2:

cd firmware/lora-2
cargo run --release

Monitor RTT Logs

probe-rs attach --chip STM32WL55JCIx

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Running the Data Pipeline

Start Infrastructure

# Start Week 7 services (InfluxDB + Grafana)
cd ~/dev/4-month-plan/wk7-mqtt-influx
docker compose up -d

# Start MQTT bridge
cd ~/dev/4-month-plan/wk10-lorawan
docker compose up -d

Verify Data Flow

# Check MQTT bridge logs
docker logs -f wk10-mqtt-bridge

# Expected output:
# [10:05:15] lora1: Temp=31.0C Hum=58.0% RSSI=-13 SNR=13.2 -> InfluxDB: OK
# [10:05:51] lora2: Temp=28.0C Hum=60.0% Press=1020.0hPa Gas=135kOhm RSSI=-17 SNR=12.0 -> InfluxDB: OK

Access Dashboard

• Grafana: http://localhost:3000 (admin/admin)
• Dashboard: Dashboards → LoRaWAN Sensor Network

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Payload Encoding

LoRa-1 (SHT41) - 4 bytes

Bytes	Type	Description	Decode
0-1	i16 BE	Temperature × 100	value / 100 = °C
2-3	u16 BE	Humidity × 100	value / 100 = %

LoRa-2 (BME680) - 12 bytes

Bytes	Type	Description	Decode
0-1	i16 BE	Temperature × 100	value / 100 = °C
2-3	u16 BE	Humidity × 100	value / 100 = %
4-5	u16 BE	Pressure × 10	value / 10 = hPa
6-7	u16 BE	Gas Resistance	kOhm
8-11	-	Padding	(unused)

Decode Payloads

# Decode a Base64 payload
python3 decode_payload.py CowZyA==
# Output: Temp: 27.00°C, Humidity: 66.00%

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MQTT Topics

Subscribe to gateway MQTT for debugging:

# All TOT application messages
mosquitto_sub -h 10.10.10.254 -t "application/TOT/device/#" -v

# LoRa-1 uplinks only
mosquitto_sub -h 10.10.10.254 -t "application/TOT/device/23ce1bfeff091fac/rx" -v

# LoRa-2 uplinks only
mosquitto_sub -h 10.10.10.254 -t "application/TOT/device/24ce1bfeff091fac/rx" -v

# Join events
mosquitto_sub -h 10.10.10.254 -t "application/TOT/device/+/join" -v

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Documentation

Document	Description
USERGUIDE.md	Complete setup and operation guide
HARDWARE_CONFIG.md	Detailed hardware specifications
LORAWAN_CREDENTIALS.md	Device credentials and EUIs
docs/rak7268v2-config.md	Gateway configuration
TROUBLESHOOTING_WL55.md	Common issues and solutions
CLAUDE.md	Development notes and constraints
NOTES.md	Technical learnings

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Deliverables

Gateway ✅ Complete

• RAK7268V2 deployed and configured (AU915 Sub-band 2)
• Built-in LoRa Server operational
• Application "TOT" created with OTAA credentials
• MQTT broker accessible at 10.10.10.254:1883

LoRa-1 (SHT41) ✅ Complete

• STM32WL55 hardware integration
• SHT41 sensor reading (temperature, humidity)
• SSD1306 OLED display (TX count, readings, SNR/RSSI)
• LoRaWAN OTAA join
• Uplink transmission (~30 second interval)
• LED flash on transmission

LoRa-2 (BME680) ✅ Complete

• STM32WL55 hardware integration
• BME680 sensor reading (temp, humidity, pressure, gas)
• SH1106 OLED display (TX count, readings, SNR/RSSI)
• LoRaWAN OTAA join
• Uplink transmission (~30 second interval)
• LED flash on transmission

Data Pipeline ✅ Complete

• Python MQTT bridge subscribing to gateway
• Payload decoding (both node formats)
• InfluxDB bucket and data writes
• Grafana datasource configured
• Dashboard with 10 panels

Documentation ✅ Complete

• USERGUIDE.md - Comprehensive deployment guide
• Hardware configuration documented
• Gateway configuration documented
• Troubleshooting guide

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Key Learnings

1. LoRaWAN Byte Order: EUIs must be reversed (little-endian) in firmware
2. No FPU: STM32WL55 requires integer-only math
3. SHT41 Wake-up: Sensor needs measurement command before I2C scan
4. MQTT 3.1 Protocol: RAK gateway requires older MQTT protocol version
5. Peripheral Stealing: Embassy async pattern for I2C sharing

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Performance Metrics

Metric	Value
Join Time	~7 seconds
Uplink Interval	~30 seconds
LoRa-1 Payload	4 bytes
LoRa-2 Payload	12 bytes
Typical RSSI	-15 to -80 dBm
Typical SNR	-10 to +14 dB
End-to-End Latency	<2 seconds

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Status: ✅ Week 10 Complete Last Updated: 2026-01-09