Industrial Ethernet to Serial IoT Bridge: SCADA Integration

Abstract

In this work, a Power over Ethernet device was designed with characteristics that makes it industrial grade capable. A DIN rail 3D enclosure was designed for completeness of the hardware. A new software module was developed for an existing SCADA open source solution, the software module allows the discovery and configuration of the device. The solution was tested using the modbus industrial protocol on a simulator and also on an industrial energy meter to finally highlight its configuration process and real usage.

Introduction

The WIZ750SR device is a complete solution for Ethernet to Serial devices, including even options for RS-232 and RS-485 levels. The device has an embedded firmware that allows configuration using an open source software developed by WIZnet which makes it easy for prototyping and testing. Nonetheless, the device itself needs some extra hardware to be able to effectively be used in a commercial product, different factors such as serial connectors, power supply and even a stable fixture for enclosure design are needed in order to be ready for the market. Commercial market is even different from Industrial or Electrical sector, mainly because different standards need to be meet for product acceptance but not always a product that meets with hardware standard break the barrier of acceptance, there is also a factor that plays an important role, the term to consider is Integration. An easy integration makes the product more prone to be adopted.

All these factors have been taken into consideration in this work to present a solution that meets hardware standards for the Industrial market and makes easier the work of field engineers by integrating a configuration interface in a well known open source SCADA software. Complete instructions for Integrator persons are provided but also developing details are explained.

The Industrial PoE to Serial Bridge Product

The product is based on the WIZ750SR, which is a tiny module well designed by WIZnet, especially because after studying the hardware I notice that with some minor modifications I can use the module in a PoE design. Power over Ethernet requires different hardware because the power goes along the signal lines and needs, among other things, rectification in order to extract DC level using a DC-DC converter. PoE is also well suited for the industrial market since it has isolation which is always a plus when interfacing with other equipment. In order to not lose the isolation, the WIZnet module built-in serial interfaces cannot be used, fortunately there is the TTL version that comes with I/O directly tied to WIZ750P processor. In order to make the solution as compact as possible, only one GPIO is exposed to be used as Digital Input only since it’s connected to an optically isolated device. Nonetheless, the project software module was developed with full GPIO control using the WIZnet development board.

The following images show the different sections of hardware located on the double-sided PCB.

Top View of PCB

• Yellow: External PoE Cat-5 magnetic and rectifiers

• Magenta: PoE ultra miniature SMD module

• Blue: Isolated 5V power supply

• Green: Isolated RS-485 transceiver

• Light Blue: Optocoupler input

Bottom of PCB

• Yellow: WIZ750SR module

• Blue: IDC replacement for RJ-45

• Green: RJ-45 communication signals Tx+ Tx-, Rx+ Rx-, CT.

• Light Blue: POE RJ-45 input

Bare PCB

This project uses only commercially available components, the schematics contains the part numbers for the PCB components. You also need the IDC or ribbon cable and connectors for the RJ-45 replacement. For this an 8 position ribbon cable of 1.5 inches is enough. The RJ-45 is replaced by TE Connectivity part number 215570-8 available here at mouser. Only thing is that this connector comes with a guide pin for PCB mounting which is easily removed as shown below.