Power over Ethernet - What is it ?

Power over Ethernet or as it is most commonly referred to “PoE” is a standards based implementation of power distribution using the same wiring on a twisted pair Ethernet network.

Essentially it is a method where a power source (the standard defines it as PSE - Power Source Element) is connected to the network wiring to deliver power to the other end to the cable to a device (the standard calls it the PD - Powered Device.)

This method was introduced around the year 2000 by Cisco Systems to deliver power to their new line of VoIP (Voice over IP) phones.

Basically the trick was to use the unused extra pairs on the Ethernet cable to carry DC power from the PSE to the PD. While today the most common implementation is to have the PSE integrated into the Ethernet switch, power can be “injected” in the middle of the wiring, what the standard calls Mid-Span.

To ensure interoperability the IEEE developed a standardized version of PoE as part of the 802.3 Ethernet Standard, the first version was issued on 2003 as 802.3af that defined how to deliver up to 13W of power to the PD using Cat3 or Cat5 cable, with the option of running the DC power on the same pairs as data (Mode A) or using the spare wires on 10/100BaseTX (Mode B.)

Over the years the standard evolved, first to 802.3at or PoE+ for up to ~25W and supporting Gigabit networks, to lately 802.3bt for up to 51-71W of power. The following table from Wikipedia shows a nice table with a comparison of the different PoE parameters for each version of the standard.

To optimize power usage and delivery, the standard classifies the power devices in various classes depending the amount of power they require and there is a sequencing or stages that establish how power is turned on and how much of it. IEEE 802.3 complaint implementations of PoE must follow this sort of electronic negotiation which requires a semi-smart controller on both sides of the network.

The following figure shows the stages of power negotiation and delivery for 802.3af/at

Be aware that there are non-compliant implementations of power delivery over the Ethernet cables that are improperly also called “PoE,” some of these implementations consist on just a power supply injected into the spare wires of the Ethernet cable without any negotiation/sequencing and maximum amount of power is often limited and not protected. These type of power injectors became very popular for installations of Webcams.

Over the next few weeks I’ll be publishing a series of “What is on the bench” articles about different options about how to implement and embed it on your designs for Powered devices, there are various companies that make things very easy with PoE ready modules, and others that provide the key components and reference designs.

Meanwhile here is a cool video from All about electronics with a brief explanation of PoE

Happy Networking

Cheers

Jorge

Smart Buildings and IoT

This is a very interesting TEDx Berlin presentation I had to watch for my IoT (Internet of Things) Masters course.

Surprisingly 35% of carbon emissions come from buildings, which can be substantially reduced by applying modern technologies and sustainable development.

Building automation was a subject that grabbed my attention more than 30 years ago while working at IBM with the Series/1 computer. This system was designed for real time applications, one of them building control and automation. At that time Internet was still in its early days and modern computer networks where just in their infancy. Many systems and technologies were proprietary and there was minimal interoperability, and IoT was not even on the radar screen.

Nowadays with the ubiquity of the Internet, advances in technology, particularly on IoT and Big Data, it became feasible and commercially viable and redituable to develop sustainable or smart buildings, and the same concept can be used for developing smart cities.

As shown in the TEDx presentation by Coen van Oostrom, "The Edge" building is a clear demonstration on how the convergence of modern technologies with a sustainable development approach can enable the construction of more efficient and practical commercial building.

"The Edge" is not only consider sustainable and smart just because of the technology, but also as the way it is utilized by Deloitte (the principal tenant) to create a working space where no one has a desk, a new approach that goes beyond coworking spaces, in this case it is called hotdesking.

Your desk or space on the building is allocated based on your plans and preferences for the day. You drive an electric car, no problem the parking on the building includes plenty of charging places and your vehicle is recognized by its license plate and you are directed to your parking spot for the day.

What is what you do ?

Once in a while I find myself in the situation of having to answer the classic recurring  question: "What is what you do?".

It is not rocket science, but I don't have an easy answer in few words given that they won't convey the deep complexity, knowledge and dedication for what I've been doing for a very long time.

The simple and short answer would be "Electronic Systems Design", or when people may know what I'm talking about "Embedded Systems Design", and expanded answer would be "Research and Development of Embedded Microcontroller Applications with Networking and Intelligent Graphical Human Interfaces and Internet of Things connectivity." 

WOW, that sounds pretty kewl and geeky, IT IS !!, well at least for me :-)

To give you a more mundane and simple example, there is a lot of people talking about "smart" things like the nest thermostat, well, I design the guts of that kind of stuff.

Let me share with you how the process is, and as the saying goes, one image is worth a thousand words, but I'll add a brief explanation of each step.

The images above are for one of the products I developed and sold through my website, it is a circuit board slightly smaller than a credit card and that has a network interface chip, a simple microcontroller as the main processor and some non volatile memory.

The microcontroller is programmed with the "firmware" that implements the TCP/IP protocols used to communicate over the Internet, and it has sort of a small web server, that once the board is connected to the Net and powered, will let you access it from anywhere around the world to turn things off/on, check sensor readings like temperature, etc.

Like many ideas, a product like this may start as some gibberish block diagram on a napkin, the back of a store receipt, etc., but it then a more formal process begins using the right tools for the job.

The first step is to identify what components will be used and research how they have to be interconnected and what stuff is needed to make them work. Also for more complex designs and particular components the process includes testing and validating the components using "Eval Boards or Kits" or just samples.

Then using a specific CAD program (Computer Aided Design), in the past I used Eagle Cad (now owned by Autodesk) but several years ago I converted into Altium. There are many other CAD programs available including the very popular one called KiCad.
These CAD tools when used on the Electronics Design process are often called EDA for Electronic Design Automation, essentially the assist you to  capture a representation of a component (called a symbol) and its package layout or footprint for later use in the design of a circuit board. Once you have the symbols you can put together the schematics (shown as 1 in the picture), that show all the components, its values and how they need to get interconnected.

Not always necessary but a second step would be to put a rough prototype of the design to test its functionality, in some cases this could be done with a simulator on a computer, but there is no better test than the real hardware. In this case (shown as 2) I put together a wire wrapped prototype (components are interconnected on the bottom by thin wires that get "wrapped" on the pins of the sockets or the leads of the components.)

If everything goes well with the prototype, the next step is to design the printed circuit board layout (shown as 3), again with the EDA program, this consists in placing the components and drawing the traces in one, two or more layers of conductive material that will interconnect them. When multiple layers are used on a circuit board we create a sandwich of conductive and non-conductive materials, what we call the "PCB Layer Stack" or just "Stackup."

The EDA program will generate a set of special files that will be used for Computer Aided Manufacturing (CAM), this includes the files to produce the circuit board, place and solder the components on it. Picture 4, shows another tool I frequently use to inspect the CAM files.

Again, not always but often, just a few printed circuit board prototypes get done for testing and verification, to save costs (shown as 5) this particular prototype has no solder mask (a green protective and non-conductive thin layer) or legends.

If everything goes well then, real production begins (6 and 7), and the boards get programmed and tested, put into antistatic bags and get ready for shipment around the world.

Being this simple board, or a more complex design like the nest thermostat, it may require lots of research to learn the specifics of each components, some of them like more advanced microcontrollers have hundreds or thousands of pages of documentation that I need to read and digest, and experimentation using development kits, others prototype boards, etc. 

The picture on top of this article shows a partial peek to my collection of development boards, evaluation kits and my own products and prototypes.