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Wireless Lora RF Receiver Module Ra-02 Ai-Thinker 10KM 433MHZ SX1278
Ra-02 can be used for ultra-long distance
spread spectrum communication, and compatible
FSK remote modulation and demodulation
quickly, to solve the traditional wireless design
can not take into account the distance,
anti-interference and power consumption.
Ra-02 can be widely used in a variety of
networking occasions, for automatic meter
reading, home building automation, security
systems, remote irrigation systems, is the ideal
solution for things networking applications.
Ra-02 is available in SMD package and can
be used for rapid production by standard SMT
equipment. It provides customers with high
reliability connection mode.
While designing an internet of things (IoT) project that also required along radio-frequency link, it occurred to me that there are pre-wired modules already built to do that. In fact, not only do they exist as low-cost, easy-to-buy modules, but most of them already have flexible options for enhancements. When asking for advice, my friendly editor-in-chief, Adam Carlson, drew my attention to today’s LoRa modules. Just thereafter, I ordered a couple of cheap LoRa modules for my next experiments.
A few words about LoRa
Here are some basic points about LoRa and what to know when playing with it. LoRa is a robust, low-power, long-range wireless protocol developed by Semtech. LoRa entails a clever type of modulation similar to frequency modulation (FM) but is, in fact, a proprietary and patented chirp spread-spectrum (CSS) modulation. This CSS modulation is extremely resistant to noise and even to the Doppler effect, making it very useful when communicating over a long range using low power.
The basic principle is that information is encoded using chirp (a gradual increase or decrease in the frequency of the carrier wave over time). Before sending a message, the LoRa transmitter will send out a chirp signal to check that the band is free to send the message. Once the LoRa receiver has picked up the preamble chirp from the transmitter, the end of the preamble is signalled by the reverse chirp, which tells the LoRa transmitter that is it clear to begin transmission.
Fortunately, LoRa chips and modules are very cheap and easily available nowadays. The most popular one is the SX1278 transceiver chip manufactured by Semtech. Tiny modules based on SX1278 can be bought for as little as $6. Because LoRa uses unlicensed frequencies in ISM bands that are available worldwide (for example, a 433-MHz band for Asia), anyone can freely try them without having to acquire a license. However, always obey the relevant legal regulations of your country as some “radio” restrictions (output power/bandwidth limit, for instance) may apply.
Preparing the LoRa transceiver module
If you have the same XL1278-SMT module that I bought, it’s going to be pretty tricky to solder the connections because of the tiny castellated solder pads/holes in a single row (the common 2.54-mm male-header strip won’t fit on the transceiver pins as spaces between the pads are shorter than usual). I couldn’t find a suitable adapter board for the module, so I used a couple of “loose” header pins with a flake of perforated circuit board to build a quick test setup. I’ve soldered the module as shown in the figures below (I didn’t solder all pins because only certain connections are required for a quick test). The first thing that I soldered is the spring antenna as it’s crucial for safe and proper operation of the LoRa transceiver module (running without a proper antenna will kill the module at once). Remember, you need a set of two LoRa modules for the experiments.
Understanding the XL1278-SMT LoRa module
Let’s go through all key parts of the XL1278-SMT module (also known as the miniSX1278 LoRa module) to see what they actually do. According to the user manual, the tiny module operates at 1.8 V to 3.6 V with extremely low standby current, which makes it suitable for battery-powered applications. Below is the layout and pin description of the module (artwork prepared by me).
As clearly stated in the intro, at the heart of the module is one SX1278 LoRa transceiver chip from Semtech. Besides that, there’s a thin SMD crystal and an antenna matching circuit. The three-pin chip marked as “2Bt” is an NPN general-purpose transistor BC849W from Nexperia. The six-pin chip marked “G4C” is a GaAs MMIC L, S-band SPDT switch from NEC that operates with 2.5 V to 5.3 V from 50 MHz to 3 GHz. Below are the pin descriptions for the XL1278-SMT module.
|1||GND||Ground (0 V)|
|5||VCC||Power (3.6 V Maximum)|
|6||MISO||SPI Data Output|
|7||MOSI||SPI Data Input|
|9||NSS||SPI Chip Select|
|12||GND||Ground (0 V)|
|13||GND||Ground (0 V/ANT GND)|
|14||ANT||Antenna (50-Ω Impedance)|
It’s worthy to note that the recommended supply voltage of the module is 1.8 V to 3.6 V. It’s compatible with Arduino and provides a means of communication over several hundreds of meters while keeping the power demand as low as 120 mA typical for transmission and 12 mA for reception. As far as I know, most of the SX1278 modules use 3.3-V logic. While interfacing 3.3-V logic of the module with 5-V logic of the Arduino, it’s always good to have some sort of bi-directional logic-level translation going on. I’ve opted to leave it off and make my quick test setup smaller. Anyway, before moving forward, I’ll try to do some research on this and post updates here.
A block diagram of the SX1278 chip is shown below. For in-depth reading, download the (132 pages) published by .
All of that sounds pretty good, right? Well, there’s still one more step: initial testing of the LoRa module(s). In addition to an Arduino Uno board, you’ll need a dedicated library developed for the SX1278. Even though the most popular library is the one by , I’d like to introduce another one — the . The LoRaLib library can be used with any LoRa module if it’s based on one of the supported chips: SX1272 or SX1273, SX1276, SX1277, SX1278 or SX1279, RFM95, RFM96, RFM97, or RFM98. Because LoRaLib is still early in development, new core features might be added and the ones that are already implemented might be changed at any time. So it’d be better to watch the repository for updates.
The hardware setup is pretty simple, so it’s probably easier to just refer to the table below: