Building an STM32-Based LoRaWAN Gateway

This guide covers how to turn an STM32 microcontroller into a LoRaWAN gateway capable of communicating with The Things Network (TTN), ChirpStack, or other LoRaWAN networks. We'll explore both single-channel and multi-channel gateway designs.

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1. LoRaWAN Gateway Overview

Key Components

Gateway Types

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2. Hardware Setup

Option 1: Single-Channel Gateway (Beginner)

• STM32 Board: STM32F4/F7/H7 (e.g., NUCLEO-F767ZI)

• LoRa Module: SX1276 (RFM95W, RA-02)

• Connectivity: Ethernet/Wi-Fi for backhaul

Wiring:

SX1276    STM32
=================
VCC    →  3.3V
GND    →  GND
SCK    →  SPI_SCK (PB3)
MISO   →  SPI_MISO (PB4)
MOSI   →  SPI_MOSI (PB5)
NSS    →  GPIO (PB6)
RESET  →  GPIO (PB7)
DIO0   →  EXTI (PC13)

Option 2: Multi-Channel Gateway (Professional)

• STM32 Board: STM32MP1 (Linux-capable)

• LoRa Concentrator: SX1301/SX1302 (e.g., RAK2287)

• Backhaul: Ethernet, LTE, or Wi-Fi

Wiring:

RAK2287    STM32MP157
=====================
SPI       →  SPI1
GPIO      →  Reset & Interrupts
USB       →  Optional (for firmware updates)

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3. Software Setup

A. Single-Channel Gateway (Basic)

1. Flash Semtech Packet Forwarder

   • Use LoRaMac-node (STM32 port)

   • Configure lorawan_prov.h for your region (EU868/US915):

     c

       #define LORAMAC_REGION_US915  // or EU868
     

2. TTN Integration

   • Register gateway on The Things Network Console

   • Update global_conf.json:

     json

       {
         "gateway_ID": "B827EBFFFE123456",
         "server_address": "router.eu.thethings.network",
         "serv_port_up": 1700,
         "serv_port_down": 1700
       }
     

3. Run Packet Forwarder

   bash

    ./lora_pkt_fwd
   

B. Multi-Channel Gateway (Advanced)

1. Use Raspberry Pi + STM32 Hybrid

   • Run Semtech UDP Packet Forwarder on RPi

   • STM32 handles SPI communication with SX1301

2. ChirpStack Setup

   bash

    # Install ChirpStack Gateway Bridge
    sudo apt-get install chirpstack-gateway-bridge
   

3. Configure STM32 SPI Driver

   • Modify Linux device tree (spidev overlay)

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4. STM32 Code Examples

A. LoRaWAN Node Simulation (Testing)

c

// Based on LoRaMac-node
void SendFrame() {
  uint8_t payload[] = {0x48, 0x65, 0x6C, 0x6C, 0x6F}; // "Hello"
  LoRaMacStatus_t status = LoRaMacMcpsRequest(&mcpsReq);
  if (status == LORAMAC_STATUS_OK) {
    HAL_UART_Transmit(&huart1, "Frame sent!\r\n", 12, 100);
  }
}

B. Gateway Packet Forwarding

c

// Pseudocode for SPI LoRa RX
void HAL_GPIO_EXTI_Callback(uint16_t GPIO_Pin) {
  if (GPIO_Pin == DIO0_Pin) {
    uint8_t rxBuffer[256];
    SX1276_ReadFifo(rxBuffer, packetLength);
    UDP_SendToServer(rxBuffer); // Forward to TTN
  }
}

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5. Network Server Integration

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6. Antenna & Range Optimization

• Frequency: Match antenna to EU868/US915

• Placement: Elevated, clear line-of-sight

• Cable Loss: Use low-loss RG316 for long runs

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7. Troubleshooting

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8. Project Ideas

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Where to Go Next?

• Explore LoRaWAN Class A/B/C

• Add GPS for Gateway Geolocation

• Implement Secure Join (OTAA/ABP)