0. Overview of LoRa

concept

LoRa (Long Range) is a long-range, low-power wireless communication technology designed for Internet of Things (IoT) and remote sensing applications. LoRa technology is based on half-duplex modulation and provides reliable communication connections through spread spectrum and forward error correction coding.

Main features of LoRa technology

Long-distance transmission: LoRa technology uses low-power spread-spectrum modulation to achieve long-distance transmission by extending the signal to a wider spectral bandwidth. Compared with narrowband modulation technology, LoRa can transmit a longer distance at the same power.
Low power consumption: When the LoRa device transmits data, it can send a large amount of data in a short time, and then enter the sleep state at a longer interval, thereby realizing low-power communication. This is very important for battery powered IoT devices to extend the battery life of the device.
Large capacity: LoRa technology can support a large number of devices to communicate at the same time, and has a high network capacity. It uses collision avoidance and allocation of multi-channel access technology, which effectively reduces communication collisions and conflicts.
Strong anti-interference ability: LoRa technology has strong anti-interference ability in design, and can work stably in harsh environments. It adopts wideband spread spectrum modulation and forward error correction coding, which can effectively resist multipath fading, noise and interference signals.
Flexibility: LoRa technology can operate in different frequency bands and can be configured according to specific application needs and regional regulations. LoRa devices can use global open ISM frequency bands, such as 868 MHz, 915 MHz and 433 MHz.

How LoRa technology works

Signal coding: The sending end performs forward error correction coding on the data to be transmitted, adding redundant information to improve data reliability.
Spread spectrum modulation: The transmitter uses spread spectrum technology to spread the signal to a wider spectral bandwidth. Through spread spectrum, the energy of the signal is distributed in a wider frequency range, thereby improving the anti-interference ability of the signal.
Collision avoidance and access: The access mechanism avoids collisions and conflicts between nodes through multiple channels. LoRa devices use a protocol called ALOHA for collision avoidance.
Continue to explain the working principle of LoRa technology:
Reception and demodulation: The receiver listens to the transmission channel on the selected frequency and uses the LoRa modem to demodulate the signal. The demodulator restores the received spread spectrum signal to the original data.
Forward error correction decoding: The receiving end performs forward error correction decoding on the demodulated signal to correct possible transmission errors. With redundant information, the original data can be recovered.
Data extraction: The receiving end extracts valid data from the decoded signal, and performs corresponding processing and application.

LoRa technology can be applied to various IoT and remote sensing applications, such as smart city, smart agriculture, environmental monitoring, smart home, etc. LoRa devices have the characteristics of long-distance transmission, low power consumption and strong anti-interference ability, which can meet the requirements of large-scale IoT deployment.

1. Common LoRa modules

Semtech SX1276/SX1278: Semtech's SX1276 and SX1278 chips are the core of LoRa wireless communication. They support multiple frequency bands (such as 868 MHz, 915 MHz, etc.), providing the ability of long-distance transmission and low power consumption. These chips integrate LoRa modem, forward error correction coding and spread spectrum technology, which can realize highly reliable communication. Developers can use SX1276/SX1278 chips to design their own LoRa modules, or choose off-the-shelf modules integrated with these chips for development.
Microchip RN2483/RN2903: Microchip's RN2483 and RN2903 are LoRa modules that integrate the SX1276/SX1278 chip. They support the LoRaWAN protocol and provide an easy-to-use serial interface. These modules have rich functions, including device management, security authentication and data transmission, etc., and can be easily connected to the LoRaWAN network for communication.
RAK Wireless RAK811: RAK811 is a LoRa module based on SX1276 chip and STM32 microcontroller. It supports multiple frequency bands and LoRaWAN protocol, and has rich interface options (such as UART, I2C, etc.). The RAK811 module provides easy-to-use software development tools and sample codes to facilitate developers to quickly get started and develop LoRa applications.
Ebyte E32: The E32 series LoRa module launched by Ebyte is based on the SX1278 chip. These modules support multiple frequency bands and long transmission distances. The E32 module has a simple UART interface and low power consumption, making it suitable for embedded applications and IoT device integration.
Dragino Technology LG01: LG01 is a LoRa gateway module which integrates SX1276 chip and OpenWrt system. It can be used as the central node of the LoRa network, connecting multiple LoRa devices to communicate with the cloud platform. LG01 module has Ethernet interface and UART interface, supports LoRaWAN protocol and data packet forwarding function.

These LoRa modules are all common choices in the market, they provide different functions and interface options, suitable for various LoRa application scenarios. Developers can choose appropriate modules to develop and integrate LoRa applications according to their specific needs. When selecting a module, factors such as frequency band support, power consumption requirements, interface compatibility, and reliability need to be considered.

2. Semtech SX1278

Frequency band support: SX1278 supports multiple frequency bands, including commonly used frequency bands such as 433 MHz, 868 MHz and 915 MHz. This makes it adaptable to different wireless communication needs on a global scale.
Long-distance transmission: SX1278 utilizes spread spectrum technology to realize long-distance transmission. It provides better transmission distance and penetration by spreading the signal over a wider spectral bandwidth. Compared with traditional narrowband modulation technology, SX1278 can achieve longer communication distance under the same power.
Low power consumption: SX1278 is designed to optimize power consumption, suitable for battery-powered applications. It supports fast turn-on and turn-off times, enabling fast entry and exit from low-power modes, thereby extending the battery life of the device.
Anti-interference ability: SX1278 has strong anti-interference ability and can work stably in the environment of noise and interference. It adopts forward error correction coding and efficient demodulation algorithm, which can effectively reduce the transmission error rate and provide reliable connection under harsh communication conditions.
Multiple communication interfaces: SX1278 provides a variety of communication interfaces, including SPI and GPIO. These interfaces enable SX1278 to connect and communicate with microcontrollers or other external devices.
LoRaWAN Compatible: The SX1278 is compatible with the LoRaWAN protocol, enabling it to be integrated with LoRaWAN networks. LoRaWAN is a low-power wide-area network protocol that provides functions such as device management, security authentication, and data transmission for IoT devices.

When using the SX1278 for LoRa application development, developers can use the development tools and software libraries provided by Semtech, such as the Semtech LoRaWAN library. These tools and libraries provide rich function interfaces and sample codes to help developers quickly get started and develop LoRa applications.

SX1278 is a powerful LoRa radio frequency transceiver chip with the characteristics of long-distance transmission, low power consumption and strong anti-interference ability. It is an essential part of building a reliable LoRa communication system.

3. STM32 uses SX1278

method

Hardware connection:
- Connect the SX1278 chip with the STM32 microcontroller. Usually, SX1278 communicates with STM32 through SPI interface, so you need to connect SPI pins (such as SCK, MISO, MOSI) and chip select pins (NSS/CS). At the same time, connect control pins (such as reset pins, interrupt pins) and power pins (VCC and GND).
- Make sure that the pins of the STM32 and the pins of the SX1278 chip correspond correctly. You can refer to the data sheet of the SX1278 chip and the pin mapping table of the STM32.
Configure the SPI interface:
- Configure the SPI interface on the STM32, set the SPI clock rate, data bit width and mode and other parameters. You can use the SPI driver library provided by STM32 or directly manipulate the registers to configure the SPI interface.
Initialize the SX1278 chip:
- Write the initialization code on STM32, and configure the SX1278 chip with parameters suitable for your application needs. This includes setting parameters such as working mode (such as sleep mode, receiving mode, transmitting mode), frequency channel, spreading factor, bandwidth, and transmitting power. You can refer to the datasheet of the SX1278 chip for available configuration options and register settings.
Send and receive data:
- Write code to send data and receive data on STM32. For sending data, you need to write the data to be sent into the sending buffer of the SX1278 chip, and trigger the sending operation. For receiving data, you need to enable the receive mode and wait for the receive interrupt or poll the receive status, and then read the received data from the receive buffer of the SX1278 chip.
Data processing:
- Write the corresponding code on STM32 to process the sent and received data. This may involve data decoding, error detection, checksums, and other application-specific operations. According to your application requirements, you can use different data processing algorithms and functional modules.

sample code

#include "stm32f4xx.h"
#include "stm32f4xx_spi.h"
#include "stm32f4xx_gpio.h"

#define SX1278_NSS_PIN GPIO_Pin_0
#define SX1278_NSS_PORT GPIOA

SPI_InitTypeDef SPI_InitStruct;

void SPI_Configuration(void)
{
    
    
    GPIO_InitTypeDef GPIO_InitStruct;

    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_SPI2, ENABLE);

    // SPI2 GPIO Configuration (PA5 -> SCK, PA6 -> MISO, PA7 -> MOSI)
    GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AF;
    GPIO_InitStruct.GPIO_OType = GPIO_OType_PP;
    GPIO_InitStruct.GPIO_PuPd = GPIO_PuPd_DOWN;
    GPIO_InitStruct.GPIO_Speed = GPIO_Speed_50MHz;

    GPIO_InitStruct.GPIO_Pin = GPIO_Pin_5 | GPIO_Pin_6 | GPIO_Pin_7;
    GPIO_Init(GPIOA, &GPIO_InitStruct);

    GPIO_PinAFConfig(GPIOA, GPIO_PinSource5, GPIO_AF_SPI2);
    GPIO_PinAFConfig(GPIOA, GPIO_PinSource6, GPIO_AF_SPI2);
    GPIO_PinAFConfig(GPIOA, GPIO_PinSource7, GPIO_AF_SPI2);

    SPI_InitStruct.SPI_Direction = SPI_Direction_2Lines_FullDuplex;
    SPI_InitStruct.SPI_Mode = SPI_Mode_Master;
    SPI_InitStruct.SPI_DataSize = SPI_DataSize_8b;
    SPI_InitStruct.SPI_CPOL = SPI_CPOL_Low;
    SPI_InitStruct.SPI_CPHA = SPI_CPHA_1Edge;
    SPI_InitStruct.SPI_NSS = SPI_NSS_Soft;
    SPI_InitStruct.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_256;
    SPI_InitStruct.SPI_FirstBit = SPI_FirstBit_MSB;
    SPI_InitStruct.SPI_CRCPolynomial = 7;
    SPI_Init(SPI2, &SPI_InitStruct);

    SPI_Cmd(SPI2, ENABLE);
}

void SX1278_WriteByte(uint8_t addr, uint8_t data)
{
    
    
    GPIO_ResetBits(SX1278_NSS_PORT, SX1278_NSS_PIN);

    SPI_I2S_SendData(SPI2, addr | 0x80); // Set the MSB to indicate write operation
    while (SPI_I2S_GetFlagStatus(SPI2, SPI_I2S_FLAG_BSY) != RESET);
    SPI_I2S_ReceiveData(SPI2);

    SPI_I2S_SendData(SPI2, data);
    while (SPI_I2S_GetFlagStatus(SPI2, SPI_I2S_FLAG_BSY) != RESET);
    SPI_I2S_ReceiveData(SPI2);

    GPIO_SetBits(SX1278_NSS_PORT, SX1278_NSS_PIN);
}

uint8_t SX1278_ReadByte(uint8_t addr)
{
    
    
    uint8_t data;

    GPIO_ResetBits(SX1278_NSS_PORT, SX1278_NSS_PIN);

    SPI_I2S_SendData(SPI2, addr & 0x7F); // Set the MSB to indicate read operation
    while (SPI_I2S_GetFlagStatus(SPI2, SPI_I2S_FLAG_BSY) != RESET);
    SPI_I2S_ReceiveData(SPI2);

    SPI_I2S_SendData(SPI2, 0x00); // Send dummy data to receive the actual data
    while (SPI_I2S_GetFlagStatus(SPI2
(SPI2, SPI_I2S_FLAG_BSY) != RESET);
    data = SPI_I2S_ReceiveData(SPI2);

    GPIO_SetBits(SX1278_NSS_PORT, SX1278_NSS_PIN);

    return data;
}

void SX1278_Configuration(void)
{
    
    
    // Reset SX1278
    GPIO_ResetBits(SX1278_NSS_PORT, SX1278_NSS_PIN);
    // Delay for a short time
    GPIO_SetBits(SX1278_NSS_PORT, SX1278_NSS_PIN);
    // Delay for a short time

    // Configure SX1278 settings
    SX1278_WriteByte(0x01, 0x88); // Sleep mode
    SX1278_WriteByte(0x06, 0x6C); // Frequency: 915MHz
    SX1278_WriteByte(0x0E, 0x00); // Power Amplifier: PA_BOOST
    SX1278_WriteByte(0x0F, 0x0E); // Output Power: 14dBm
}

void SX1278_SendData(uint8_t* data, uint8_t len)
{
    
    
    // Configure SX1278 to transmit mode
    SX1278_WriteByte(0x01, 0x81); // Standby mode
    SX1278_WriteByte(0x01, 0x83); // Transmit mode

    // Send data
    for (uint8_t i = 0; i < len; i++) {
    
    
        SX1278_WriteByte(0x0D, data[i]);
    }

    // Wait for transmission to complete
    while ((SX1278_ReadByte(0x12) & 0x08) == 0x00);

    // Configure SX1278 back to standby mode
    SX1278_WriteByte(0x01, 0x81); // Standby mode
}

int main(void)
{
    
    
    uint8_t data[] = {
    
    0x01, 0x02, 0x03, 0x04, 0x05};
    uint8_t len = sizeof(data);

    SPI_Configuration();
    SX1278_Configuration();

    while (1) {
    
    
        // Send data using SX1278
        SX1278_SendData(data, len);

        // Delay before sending the next data
        for (volatile int i = 0; i < 1000000; i++);
    }
}

The above sample code implements the basic functions of LoRa communication using SX1278 on STM32 microcontroller. In the main function, first configure SPI and SX1278, and then SX1278_SendDatasend data by calling the function. You can modify the data content and sending frequency according to your own needs. Make sure to do proper configuration and pin mapping according to your hardware connection.

Detailed explanation of LoRa module (SX1278)

LoRa module (SX1278)