IIoT Edge Development

This chapter describes the process of prototyping a device for beginners. We provide detailed instructions on how to assemble four different prototypes, and how to build and run simple IoT apps for the prototypes, together with sample source code. Finally, we explore the Predix services that can be used to store, analyze, and merge the sensor data from the prototypes.

In this chapter, you will learn about the following topics:

• Choosing hardware for prototyping
• The Open Systems Interconnection model and its layers
• Application-layer protocols—HTTP and WebSocket
• Industrial M2M protocols—Modbus and OPC UA
• Assembling a device for a prototype
• Preparing an SD card for a prototype
• Building and running simple IoT apps using the HTTP, WebSocket, Modbus, and OPC UA protocols
• Data management services in Predix

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Hardware for prototypes

This section overviews the available variety of hardware that can be used for prototyping, and gives some tips on choosing the hardware and a data exchange protocol to ensure communication between the components of a prototype.

Variety and cost

One can find a variety of open source hardware for prototyping—Arduino, Raspberry Pi, Orange Pi, LinkIt, BeagleBone, and Tessel. Most of them are really cheap; you can buy an Orange Pi for just $33. The price usually depends on how powerful the board is and what interfaces it supports.

In addition to a board, it is possible to purchase a starter kit that usually costs about $70. It includes a few sensors, a small display, lamps, cables, and a breadboard...

Application-level protocols – HTTP

In this section, we will try to build a simple IoT application for sending data from a DHT-12 temperature and humidity sensor to a receiver device, using a Raspberry Pi hub and the HTTP protocol:

Data flow from a DHT-12 sensor to a receiver

Offering a variety of usage options, HTTP is one of most popular protocols on the web. Every time you open a website or run a mobile application, it is most likely the HTTP protocol you are using.

In the following table, you can find a more detailed description of the protocol to understand whether it is suitable for your needs:

Key	Value
Open source	Yes
OSI layer	Application
Data types	Text, HTML, script, style, font, JSON, XML, stream, binary
Limitations	Not suitable for large amounts of binary data
Possible operations	Send/receive data
Latency	Low
Usage...

Application-level protocols – WebSocket

In this section, we will try to build a simple IoT app for sending data from an XD-80 light sensor module to a receiver device, using a Raspberry Pi hub and the WebSocket protocol:

Data flow from an XD-80 sensor to a receiver device

WebSocket is most widely used in the case that one needs to enable fast transfer of real-time data. The protocol allows for two-way interaction between a client and a server, and for streaming multiple messages using the same TCP connection, which lowers the communications overhead.

In the following table, you can find a more detailed description of the protocol to understand whether it is suitable for your needs:

Key	Value
Open source	Yes
The OSI layer	Application
Data types	String
Limitations	Not suitable for large amounts of binary data
Possible operations	Send...

Industrial M2M protocols – Modbus

In this section, we will try to build a simple IoT application for sending data from a sensor simulator module to a receiver device (a PC or a cloud), using a Raspberry Pi hub and the Modbus protocol:

Data flow from a sensor simulator to a receiver device

For devices with limited hardware resources, it makes sense to use the Modbus protocol for serial communication. While simple, it has several open and proprietary implementations that vary in functionality.

Note that this protocol can be used on the transport layer, but, in our example, we are going to use Modbus TCP, working on the application level.

In the following table, you can find a more detailed description of the protocol to understand whether it is suitable for your needs:

Key	Value
Open source	Yes*
The OSI layer	Transport or an application
Data types ...

Industrial M2M protocols – OPC UA

In this section, we will try to build a simple IoT app for sending data from a sensor simulator module to a receiver device (a PC or a cloud), using a Raspberry Pi hub and the OPC UA protocol:

Data flow from a sensor simulator to a receiver device

The OPC UA protocol is similar to Modbus, but works with more data types, and has no serious limitations, while providing for security, compression, and low latency.

The protocol was developed by the OPC Foundation as an industrial machine-to-machine communication protocol. OPC UA is an improved version of the Open Platform Communications (OPC) protocol, with one of the major changes being that the new protocol is available free of charge without any restrictions.

In the following table, you can find a more detailed description of the protocol to understand whether it is suitable for your needs...

Data management options in Predix

To ensure storing, analyzing, and merging the sensor data we have collected in our Raspberry Pi hubs, we need to use specialized data management solutions. Predix offers a good selection of services for this purpose, as listed here:

• Asset
• Event Hub
• Time Series
• Database as a Service
• Blobstore
• Message Queue (AMQP)
• Key-Value Store:

Data management services in the Predix catalog

You can select any of the services, depending on your data type and the operations you need to perform. In particular, for our application that handles time series data, we can use the Time Series storage.

The following subsections describe the data management services offered by Predix (https://www.predix.io/catalog/services/) in more detail, highlighting their features and the purposes for which they are usually used.

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Summary

In this chapter, we gave tips on choosing hardware and a data exchange protocol for a prototype. We also described how to assemble a prototype with different sensors and build and run four types of applications, one for each of the protocols—HTTP, WebSocket, Modbus, and OPC UA. In addition, we overviewed the Predix services for storing, analyzing, and merging the sensor data from the prototypes.

In the next chapter, you will learn about data management techniques and their implementations for the IIoT stack.