The elegance of Power over Ethernet (PoE) is that you can provide network connectivity and power over a single cable. Unfortunately not nearly enough hardware seems to support this capability, forcing intrepid hackers to take matters into their own hands. The latest in this line of single-cable creations is this beautiful Vacuum Fluorescent Display (VFD) clock from [Glen Akins].
One of the key advantages VFDs have over their Nixie predecessors is greatly reduced energy consumption, and after [Glen] ran the numbers, he saw that a display using six VFD tubes could easily be powered with standard PoE hardware. With this information, he started designing the PCB around the early 1990s era IV-12 tube, which has the advantage of being socketed so he could easily remove them later if necessary.
[Glen] first had to create a schematic and PCB footprint for the IV-12 tube that he could import into Eagle, which he was kind enough to share should anyone else be working with these particular tubes down the line. After a test of the newly designed socket was successful, he moved onto the rest of the electronics.
The clock is powered by a Microchip PIC18F67J60, which connects to the Ethernet network and pulls the current time down from NTP. After seeing so many clocks use an ESP to connect to the Internet over WiFi, there’s something refreshing about seeing a wired version. The tube segments are driven by a HV5812, also Microchip branded. Lastly, [Glen] used a number of DC/DC converters to generate the 1.5 V, 3.3 V, 5 V, and 25 V necessary to drive all the electronics and VFDs.
Addressable LEDs are a staple of homemade Christmas decorations in our community, as is microprocessor control of those LEDs. So at first sight [Glen Akins]’ LED decorated Christmas tree looks pretty enough, but isn’t particularly unusual. But after reading his write-up you’ll discover there’s far more to the project than meets the eye, and learn a lot about the technologies behind it that has relevance far beyond a festive light show.
The decoration is powered exclusively from power-over-Ethernet, with a PIC microcontroller translating Art-Net DMX-over-Ethernet packets into commands for the LED string. The control board is designed from the ground up and includes all the PoE circuitry, and the write-up gives a very thorough introduction to this power source that takes the reader way beyond regarding PoE as simply another off-the-shelf black box. Along the way we see all his code, as well as learn a few interesting tidbits such as the use of a pre-programmed EEPROM containing a unique MAC address.
So if your house has CAT5 wiring and you want an extra dimension to your festive splendour, you’ve officially got a whole year to build your own version. He’s featured here before, with his buzzer to break the Caps Lock habit.
When the Raspberry Pi 3 Model B+ was announced in March of 2018, one of its new features was the ability to be (more easily) powered via Power-over-Ethernet (PoE), with an official PoE HAT for the low price of just twenty-one USA bucks. The thing also almost worked as intended the first time around. But to some people this just isn’t good enough, resulting in [Albert David] putting out a solution he calls “poor man’s PoE” together for about two bucks.
His solution makes it extra cheap by using so-called passive PoE, which injects a voltage onto the conductors of the network cable being used for PoE, without bothering with any kind of handshake. In general this is considered to be a very reliable (albeit non-standard) form of PoE that works great until something goes up in smoke. It’s also ridiculously cheap, with a PoE injector adapter (RJ-45 plug & 2.1×5.5 mm power jack to RJ-45 jack) going for about 80 cents, and a DC-DC buck converter that can handle the input of 12V for about 50 cents.
The rest of the $2 budget is mostly spent on wiring and heatshrink, resulting in a very compact PoE solution that plugs straight into the PoE header on the Raspberry Pi 3 board, with the buck converter outputs going into the ground and +5V pins on the Raspberry Pi’s GPIO header.
A fancier solution would implement any of the standard PoE protocols to do the work of negotiating a suitable voltage. Maybe this could be the high-tech, $5 solution featuring an MCU and a small PCB?
[Steve] bought a PoE module intended for security cameras and ran a close eye over the board to figure out what kind of hardware it was using to generate the nominal 12 V output. He identified an MP2494 step-down converter, and with the datasheet in hand found how the output voltage is configured by changing the values of resistors in the circuit. Swapping out the stock 21.5 kΩ resistor for a 57.1 kΩ one changed the output of the converter to the 5 V necessary for his electronics.
But of course that was only half of the problem solved; he still had to connect the Ethernet side of the PoE device to the Waveshare LAN8720 board that’s providing Ethernet for the ESP32. So he removed the RJ45 jack from the LAN8720 completely, and wired that directly to the connector on the PoE board. Helpfully, the PoE board had all the pins labeled on the bottom side so this wasn’t nearly as tricky to figure out as you might expect (if only it was always that easy).
[Martin Rowan] was lucky enough to get his hands on the revised Power Over Ethernet (PoE) hat for the Raspberry Pi. Lucky for us, he wrote it up for our benefit, including inspection of the new hat, it’s circuit, and electrical testing to compare to the original hardware.
You may remember the original release of the PoE hat for the Raspberry Pi, as well as the subsequent recall due to over-current issues. In testing the revised board, [Martin] powered a test load off the USB ports, and pulled over an amp — The first iteration of the PoE hat would often trip the over-current protection at 300 milliamps.
This afternoon, the redesigned PoE board was officially released, and the post mortem of the problem documented in a blog post. It’s a lesson in the hidden complexity of hardware design, as well as a cautionary tale about the importance of thorough testing, even when the product is late and the pressure is on.
The PoE hat converts 48 volt power down to a 5 volt supply for the Pi using a flyback transformer. The problem was that this transformer setup doesn’t deliver clean steady 5 volt power, but instead provides power as a series of spikes. While these spikes were theoretically in spec for powering the Pi and usb devices, some Raspberry Pis were detecting those spikes as too much current pushed through the USB ports. The official solution essentially consists of better power filtering between the hat and the Pi, flattening that power draw.
We’re looking forward to getting our hands on this new and improved PoE Hat, and using it in many project to come.
This is a remarkable bit of engineering, even though it’s just adding Power over Ethernet to a small single board computer. Mechanically, the PoE hat doesn’t increase the 3D bounding box volume of the Raspberry Pi at all. It adds cooling with a fan controlled over I2C. Even more bizarrely, the transformer is mounted in a PCB cutout, and we’re desperate to know how that was specced, designed, and assembled. Yeah, it might just be an add-on for the Raspberry Pi, but there’s some clever work that went into designing it.
The Raspberry Pi gained PoE capability with the introduction of the Raspberry Pi 3 Model B+ last March, a release that did require a slight change to the hardware and pinout of the Raspberry Pi. Compared to the Pi 3 Model B, the Pi 3 Model B+ sports a four-pin header right next to the Ethernet jack and one of the mounting holes. This is the same location of the ‘Run’ header found in the Pi 3 Model B, and probably caused much consternation to anyone who built a hat to take advantage of having a real power button on their Pi.
Nevertheless, what’s done is done, and now we have a real PoE solution for the Raspberry Pi. This is bound to be a boon for anyone who wants to build a Raspberry Pi cluster computer, or anyone who is dropping a few Pis into a server rack that already has PoE hardware.
You can pick up a PoE Pi hat through the usual suspects (Farnell, RS, and other resellers) for $20.
Implementing PoE is made interesting by the fact that not every Ethernet device wants power; if you start dumping power onto any device that’s connected, you’re going to break things. The IEEE 802.3af standard states that the device which can source power should detect the presence of the device receiving power, before negotiating the power level. Only once this process is complete can the power sourcing device give its full supply. Of course, this requires the burden of smarts, meaning that there are many cheap devices available which simply send power regardless of what’s plugged in (passive PoE).
The brain of the upgrade is a TI TPS2378 Powered Device controller, which does the power negotiation. It sits on one of two new boards, with a rudimentary heatsink provided by some solar cell tab wire. The second board comprises the power interface, and consists of dual Schottky bridges as well a 58-volt TVS diode to deal with any voltage spikes due to cable inductance. The Ethernet transformer shown in the diagram above was salvaged from a dead Macbook and, after some enamel scraping and fiddly soldering, it was fit for purpose. For a deeper dive on Ethernet transformers and their hacked capabilities, [Jenny List] wrote a piece specifically focusing on Raspberry Pi hardware.