Raspberry Pi SX1262 XXXM LoRaWAN/GNSS HAT User Guide

Introduction

This series of products are LoRa modules using the new generation of SX1262 RF chip, with the features of long communication distance and strong anti-interference ability. Suitable for Sub-GHz frequency band networks, and is available in LF (410~510MHz) or HF (850~930MHz) frequency band versions. Combined with a LoRa gateway, it can be connected to servers such as TTN to build a LoRaWAN network. In addition to the basic LoRaWAN version, it also provides an optional GNSS positioning function with GPS/BD support.

Features

• Common features:
  • Standard Raspberry Pi 40PIN GPIO header, supports Raspberry Pi series boards.
  • The new generation SX1262 has higher power efficiency and longer transmission distance than the SX1278.
  • Suitable for the Sub-GHz band, combined with the gateway, can be quickly connected to a cloud server such as TTN to build a LoRaWAN network.
• GNSS version features:
  • Onboard L76K module with GPS/BD support, provides accurate clock and location info for node module.
  • Onboard button cell holder, supports ML1220 rechargeable cell, for preserving ephemeris information and hot starts.
  • Onboard 4 LED indicators for module operating status.
  • Comes with online development resources and manual (example in C).

Parameters

Hardware Description

Hardware Selection

Hardware Connection

Pinout Definition

• CS MOSI MISO CLK is the SPI interface of SX1262, and BUSY is the status pin of SX1262.
  • Use MCU's SPI bus to communicate with Core1262-xF. When MCU reads and writes SX1262 registers, it needs to read and write parameters in the order of Opcode + Address + Data. For more information, please refer to chapters 8, 10, 11, and 12 of the datasheet. The maximum SPI speed is 18MHz. The communication is shown in the figure below.

• • When the MCU reads and writes the SX1262 register, it needs to detect the BUSY pin first. The low level indicates that it is idle and can be read and written normally, and the high level indicates that it is busy and cannot read and write the register, as shown in the figure below.

• RESET is the factory reset pin of SX1262, pull it low for 100us to restore the default parameters of the register, and keep a high level when working.
• RXEN, TXEN are RF single-pole switch (SPDT) pins, RXEN low level, TXE high level, SX1262 is in receiving mode, RXEN high level, TXEN low level, SX1262 is in transmitting mode.
• DIO1, DIO2, and DIO3 are SX1262 functional GPIO pins, which can be set as input and output to indicate various states of SX1262 (8.5 IRQ Handling in the figure below), usually, DIO1 is set as an interrupt output in the state shown in the figure below, and DIO2 is connected to RXEN Set as the control pin of the RF single-pole switch, DIO3 is set to supply power to the TCXO, for details, please refer to Datasheet 8.3.2, 8.5 summary.

Dimensions

LoRa & LoRaWAN

What is LoRa ?

Semtech's LoRa is a long-distance, low-power wireless platform for the Internet of Things (IoT), which generally refers to radio frequency chips using LoRa technology. The main features are as follows：

• The spread spectrum modulation technology adopted by LoRa (abbreviation of long range) is derived from Chirp Spread Spectrum (CSS) technology, which is one of the long-distance wireless transmission technology and LPWAN communication technology. Spread spectrum technology uses bandwidth for sensitivity technology, Wi-Fi, ZigBee, etc. all use spread spectrum technology, but the characteristic of LoRa modulation is that it is close to the limit of Shannon's theorem, and the sensitivity can be improved with maximum efficiency. Compared with traditional FSK technology, at the same communication rate, LoRa is more sensitive than FSK by 8 ~12dBm. At present, LoRa mainly operates in the ISM frequency band of Sub-GHz.

• LoRa technology integrates technologies such as digital spread spectrum, digital signal processing, and forward error correction coding, which greatly improves the performance of long-distance communication. LoRa's link budget is better than any other standardized communication technology. The main factors that determine the distance in a given environment.
• LoRa RF chips mainly include SX127X series, SX126X series, SX130X series, of which SX127X, SX126X series are used for LoRa nodes, and SX130X is used for LoRa gateways. For details, please refer to Semtech's product list.

What is LoRaWAN ?

• LoRaWAN is an open protocol for low-power wide-area networks built on LoRa radio modulation technology. Designed to wirelessly connect battery-powered "things" to the Internet in regional, national, or global networks, and target critical Internet of Things (IoT) requirements such as two-way directional communication, end-to-end security, mobility, and localized services. The node wirelessly connects to the Internet with network access authentication, which is equivalent to establishing an encrypted communication channel between the node and the server. The LoRaWAN protocol level is shown in the figure below.
  • The Class A/B/C node devices in the MAC layer basically cover all the application scenarios of the Internet of Things. The difference among them is that the time slots for nodes to send and receive are different.
  • EU868 and AS430 in the Modulation layer show that frequency band parameters are different in different countries. Please click the reference link for regional parameters.
    

• To achieve LoRaWAN network coverage in cities or other areas, it needs to be composed of four parts: node (LoRa node radio frequency chip), gateway (or base station, LoRa gateway radio frequency chip), server, and cloud, as shown in the following figure.
  
  • The DEVICE (node device) needs to initiate a network access request packet to the GATEWAY (gateway) and then to the server. After the authentication is passed, it can send and receive application data with the server normally.
  • GATEWAY (gateway) can communicate with the server through a wired network, 3/4/5G wireless network
  • The main operators on the server side are TTN, etc. For building cloud services by yourself, please refer to lorawan-stack, chirpstack

• There are two methods for Raspberry Pico and Pico-LoRa-SX1262 to connect to the network via LoRaWAN: OTAA (Over-The-Air-Activation) and ABP (Activation By Personalization). Here we use OTAA, as shown below. Also you can refer to link 1, link 2 and source code.
• Step 1: Please send the "Join-Request" message to the network to be added, and note that the adding process is always initiated by the end device. The join-Request message can be transmitted at any rate and in one of the region-specific join channels. For example: in Europe, the end device can send the join-Request message at 868.10 MHz, 868.30MHz, or 838.50MHz. Also, the message can send to the network server by one or more gateway. In addition, you need to pay attention to choosing the applicable frequency band according to the local radio management regulations. You can refer to link and LoRa Alliance for the frequency distribution table. The Join-Request message is combined by the following field, AppEUI, and DevEUI are generated by the server end.
  
  • AppEUI: A 64-bit globally unique application identifier in the IEEE EUI64 address space that uniquely identifies an entity capable of processing Join-Request frames.
  • DevEUI: A 64-bit globally unique device identifier that uniquely identifies an end device in the IEEE EUI64 address space.
  • DevNonce: A unique random 2-byte value generated by the end device. The web server uses each end device's DevNonce to keep track of their join requests. If the end device sends a join request with the previously used DevNonce (this case is called a replay attack), the network server will reject the join request and will not allow the end device to register with the network.
• Step 2: The web server handles the Join-Request-Message. If the end device is allowed to join the network, the web server will generate two session keys (NwkSKey and AppSKey) and the Join-accept message. The Join-accept message itself is then encrypted using AppKey. The web server uses AES decryption operation in ECB mode to encrypt Join-accept messages.
• Step 3: The network server sends the encrypted join to accept the message back to the end device as a normal downlink.
• Step 4: The end device uses AES to decrypt Join-Accept. And uses AppKey and AppNonce to generate two session keys NwkSKey and AppSKey for subsequent communication with the Networking server. Network Server also saves kSKey, Join server distributes AppSKey to Application Server.

• The DevEUI and AppEUI parameters used as terminal devices to access the Internet need to be registered and generated by the server. The specific process is as follows:
  • Register an account in TTS and log in. Create an Application.

• • Add an End Device

• • Configure the End Device as in the picture. Please save the DevEUI and the AppKey for further use.

Application

LoRa devices and networks such as LoRaWAN enable smart IoT applications to help solve the planet's formidable challenges in energy management, natural resource reduction, pollution control, infrastructure efficiency, disaster prevention, and more. Semtech's LoRa devices have achieved hundreds of successful use cases in smart cities, homes and buildings, communities, metrology, supply chain, logistics, agriculture, and more. LoRa networks have covered hundreds of millions of devices in more than 100 countries and are committed to a smarter planet.

This product test is based on TTS (The THINGS STACK) and Semtech SX1302 official library, if users build their own cloud server, please click to refer to lorawan-stack, chirpstack.

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