To meet the expectations of our customers who want to integrate existing solutions based on Modbus protocol with the world of IoT, we have created a device that allows to read data via Modbus RTU and transmit it via radio to networks based on LoRaWAN at a distance of up to several kilometers.

Why Modbus?

Modbus is one of the older communication protocols dedicated to industrial automation applications. Despite the fact that it was created many years ago, it still remains one of the most popular standards. The protocol is relatively simple, inexpensive, versatile and easy to implement and use. Modbus is an open standard, which allows to implement it without worrying about licenses or copyrights.

To meet the expectations of our customers who want to integrate existing solutions based on Modbus protocol with the world of IoT, we have created a device that allows to read data via Modbus RTU and transmit it via radio to networks based on LoRaWAN at a distance of up to several kilometers.

Figure 1. Example of Modbus network.

YO Modbus

The device is designed for DIN rail mounting in electrical switchboards. It occupies the width of only one module as a standard single-phase overcurrent circuit breaker. It can be powered by direct or alternating current over a wide voltage range of 6-30 VDC or 5-21 VAC respectively. The applied buck converter has an efficiency over 90% and the device itself consumes very little energy. Additionally, the device can be connected to protective earth (PE) cable so that the charges coming from the RS485 cable shielding will be slowly dissipated to the earth cable, which will lead to equipotential bonding in the Modbus network on the device side. The RS485 input on which the Modbus RTU protocol works is galvanically isolated from the rest of the device modules for maximum protection. The device in Modbus network works as a Master.

YO Modbus is a LoRaWAN end-device and so far it operates in Class A allowing to send data according to a configured schedule.

What distinguishes this device from others available on the market, operating in LoRaWAN Class A, is the ability to create up to 150 Modbus queries. In addition, the ability to build up to 30 different LoRa frames from responses received from Modbus Slave devices. There is no limit to the number of devices to which YO Modbus can send queries. The limit is only based on the number of queries. One of the first implementations of YO Modbus was to connect the device to an existing Modbus network that had been in place for years and create a configuration of dozens of Modbus queries to thirteen devices on the network.

When it comes to connecting the YO Modbus device to an existing Modbus RTU network, node has a set of configuration parameters dedicated to the RS485 standard so that connection in any network should not be a problem.

Device configuration

At this point, it is worth to focus on the configuration of the device and requests to the Modbus network. YO Modbus apart from the LoRa module has a built-in Bluetooth Low Energy module which allows wireless configuration. Simply connect to the device, download the configuration via CLI Tool or mobile application (in development), modify and/or add new parameters and upload configuration to the device. On the device from which we make the configuration, it is saved in a popular and simple JSON data exchange format. The data that is exchanged between YO Modbus and the CLI Tool is sent as serialized using Protobuf (Protocol Buffers) technology. This however I will try to describe in the next post because I have some interesting conclusions which I would like to share more widely.

Below I present parts of a sample configuration file for YO Modbus device.

Figure 4. YO Modbus example configuration file.