LoRa is an ultra-long-distance wireless transmission scheme based on spread spectrum technology adopted and promoted by Semtech. This solution is no longer limited by the compromise between power consumption and transmission distance, and provides users with a system that can achieve long distance, long battery life, and multiple nodes, and then expand into a network. At present, the frequency bands of LoRa operation include 433, 868, 915MHz, etc., while the SX1278 RF chip LoRa module operates in the 137~525MHz frequency band.
Advantages of LoRa
LoRa has obvious advantages in anti-blocking and selectivity. Compared with traditional FSK and GFSK, it has stronger anti-interference ability and longer transmission distance. At present, it is mainly used in wireless meter reading, home and building automation, wireless alarm and security systems, industrial monitoring and control, remote irrigation systems, etc. The following briefly introduces the application of the SX1278 LoRa module in wireless meter reading.
The LoRa wireless meter reading system mainly includes four parts, wireless water and gas meters (built-in LoRa module), remote transmission gateway, network server, and terminal. The following is a brief introduction to the LoRa wireless water meter reading system, which is also applicable to gas meters.
Wireless water meters are equivalent to various terminal nodes and contain LoRa modules. We need to understand their basic functions and some related parameters:
1. Collection of water volume, built-in battery voltage and temperature
How to collect the data is not described in detail here. The collected data is mainly transmitted to the main MCU through the communication interface. Commonly used communication interfaces include TTL, RS232, and RS485 interfaces. The normal working voltage range of the SX1278 chip is 1.8~3.7V, and other chips also have a certain working voltage range. Here, it is necessary to set a low voltage standard for the alarm of the low voltage of the built-in battery. The normal working temperature range of the SX1278 chip is -40~+85℃. Similarly, other chips also have a certain working temperature range. Here it is necessary to set high and low temperature standards for temperature alarms.
2. Timely upload information
The collection of data does not involve wireless communication, but the information needs to be uploaded to the network server through the gateway (the gateway is equivalent to the base station). The uploading process involves the wireless communication of the LoRa module. At this time, we need to know the modulation mode of the current SX1278 chip configuration (the SX1278 chip supports FSK modulation at the same time), operating frequency, transmit power, air rate, etc. The SX1278 chip can work in the 137~525MHz frequency band. Of course, this requires different hardware circuits. When it is in sleep mode, the current is less than 1uA; when it is in receive mode, the current is about 15mA; when it is in transmit mode, it is about 100Ma@20dBm.
3. Switch, valve control
This function is downlink communication, such as forcibly closing the valve when an alarm occurs.
4. Other alarms
Such as magnetic interference alarm, to prevent damage to the built-in module of the wireless water meter, or inaccurate data collected such as water volume, built-in battery voltage and temperature.
The remote gateway part included in the LoRa wireless water meter reading system can also be called a concentrator or a base station. Generally, a cell is distributed with a base station, which is responsible for copying and collecting LoRa wireless water meters in the entire cell.
A gateway can correspond to multiple node devices, and data collection can be realized by polling. The gateway is connected to the back-end server through standard IP. These communications can be bidirectional. The communication between the node device and the gateway is based on different communication frequencies and air transmission rates. The selection of the air transmission rate requires a trade-off between transmission distance and message delay.
As can be seen from the above, the gateway does not process the data. The function of the gateway is to receive the data from the LoRa wireless water meter, and then transmit it to the back-end server through the operator's 3G or 4G network. At the same time, the gateway can also receive commands from the back-end server and transmit the commands to the LoRa wireless water meter.
The server part of the LoRa wireless water meter reading system needs to store and process data, and also includes various systems. The server mainly includes user management system, operation management system, business system, maintenance system, etc.
The functions of the user management system include the addition of new users, the deletion and modification of old users, etc.; the functions of the operation management system include regular meter reading, water consumption statistics, table export and user query, etc.; the functions of the business system include payment entry As well as detailed statistics, low water reminders, etc.; the functions of the maintenance system include LoRa wireless water meter running status collection and fault detection.
The LoRa wireless water meter reading system also includes a user terminal, which can be a PC or a mobile APP. The function of the terminal is mainly used for user login, user water consumption query and user online payment.
With the development of the Internet of Things, the application of the SX1278 LoRa module has become more and more extensive in recent years, and the technology has become more and more mature. Companies committed to the development of RF modules are also keen on the research of the SX1278 LoRa module. For example, the SX1278LoRa serial port module of Chengdu Ebyte Electronic Technology Co., Ltd. adds an error correction algorithm to the software, which greatly enhances the anti-interference ability; even more, adds PA and LNA to the hardware, which further improves the transmission distance. promote. In general, the development of the SX1278 LoRa module has not stopped, and the application is not only in wireless meter reading.