A common sight on factory floors, stack lights are used to indicate the status of machinery to anyone within visual range. But hackers have found out you can pick them up fairly cheap online, so we’ve started to see them used as indicators in slightly more mundane situations than they were originally intended for. [Tyler Ward] recently decided he wanted his build own network controlled stack light, and thought it would double as a great opportunity to dive into the world of Power Over Ethernet (PoE).
Now the easy way to do this would be to take the Raspberry Pi, attach the official PoE Hat to it, and toss it into a nice enclosure. Write some code that toggles the GPIO pins attached to the LEDs in the stack light, and call it a day. Would be done in an afternoon and you could be showing it off on Reddit by dinner time. But that’s not exactly what [Tyler] had in mind.
On the software side [Tyler] has developed a firmware for the ESP32 that supports both Art-Net and RDM protocols, which are subsets of the larger DMX protocol. That means the controller should be compatible with existing software designed for controlling theatrical lighting systems. If you’d rather take a more direct approach, the firmware also sports a web interface and simple HTTP API to provide some additional flexibility.
If you’ve got a personal website that needs hosting or a few hundred gigabytes of files that could use a centralized storage location, the Raspberry Pi’s small size and extreme energy efficiency make it a compelling server choice compared to that curbside Pentium 4 box you’ve been trying to find a home for. All you need is something to put in.
Of course there’s no shortage of Pi case designs ready to be extruded from your 3D printer, but we recently found ourselves particularly taken with this unique one designed by [Ken Segler]. It’s not only small and sleek with a dash of futuristic flair, but it includes a front-mounted two inch 240 x 320 IPS display that connects to the Pi over SPI. At the minimum that gives you a way to see all those beautiful boot messages on startup, but with a little code, it could provide you with various system statics and status messages at a glance.
While the LCD is clearly the star of the show here, the case also has a few other nice features that make it worthy of your consideration. The magnetically attached fan filter on the the top, for one. The stacked layout that puts the Pi directly above the SSD also makes for a relatively compact final product.
One thing to note though is that [Ken] is using Power-over-Ethernet, meaning there’s no spot for a dedicated power jack on the case. It’s an easy enough feature to add into your own build, but naturally not everyone’s network is suitably equipped. In that case, beyond the normal annoyances of editing STL files, it shouldn’t be too much trouble to add one in without having to literally hack your way through the printed plastic.
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.
A remote Ethernet device needs two things: power and Ethernet. You might think that this also means two cables, a beefy one to carry the current needed to run the thing, and thin little twisted pairs for the data. But no!
Power over Ethernet (PoE) allows you to transmit power and data over to network devices. It does this through a twisted pair Ethernet cabling, which allows a single cable to drive the two connections. The main advantage of using PoE as opposed to having separate lines for power and data is to simplify the process of installation – there’s fewer cables to keep track of and purchase. For smaller offices, the hassle of having to wire new circuits or a transformer for converted AC to DC can be annoying.
PoE can also be an advantage in cases where power is not easily accessible or where additional wiring simply is not an option. Ethernet cables are often run in the ceiling, while power runs near the floor. Furthermore, PoE is protected from overload, short circuiting, and delivers power safely. No additional power supplies are necessary since the power is supplied centrally, and scaling the power delivery becomes a lot easier.
Devices Using PoE
VoIP phones are becoming increasingly prevalent as offices are opting to provide power for phones from a central supply rather than hosting smaller power supplies to supply separate phones. Smart cameras – or IP cameras – already use Ethernet to deliver video data, so using PoE simplifies the installation process. Wireless access points can be easily connected to Ethernet through a main router, which is more convenient than seeking out separate power supplies.
Other devices that use PoE include RFID readers, IPTV decoders, access control systems, and occasionally even wall clocks. If it already uses Ethernet, and it doesn’t draw too much power, it’s a good candidate for PoE.
On the supply side, given that the majority of devices that use PoE are in some form networking devices, it makes sense that the main device to provide power to a PoE system would be the Ethernet switch. Another option is to use a PoE injector, which works with non-PoE switches to ensure that the device is able to receive power from another source than the switch.
How it Works
Historically, PoE was implemented by simply hooking extra lines up to a DC power supply. Early power injectors did not provide any intelligent protocol, simply injecting power into a system. The most common method was to power a pair of wires not utilized by 100Base-TX Ethernet. This could easily destroy devices not designed to accept power, however. The IEEE 802.3 working group started their first official PoE project in 1999, titled the IEE 802.3af.
This standard delivered up to 13 W to a powered device, utilizing two of the four twisted pairs in Ethernet cabling. This was adequate power for VoIP phones, IP cameras, door access control units, and other devices. In 2009, the IEEE 802.3 working group released the second PoE standard, IEEE 802.3at. This added a power class that could deliver up to 25.5 W, allowing for pan and tilt cameras to use the technology.
While further standards haven’t been released, proprietary technologies have used the PoE term to describe their methods of power delivery. A new project from the IEEE 802.3 working group was the 2018 released IEEE 802.3bt standard that utilizes all four twisted pairs to deliver up to 71 W to a powered device.
But this power comes at a cost: Ethernet cables simply don’t have the conductive cross-section that power cables do, and resistive losses are higher. Because power loss in a cable is proportional to the squared current, PoE systems minimize the current by using higher voltages, from 40 V to 60 V, which is then converted down in the receiving device. Even so, PoE specs allow for 15% power loss in the cable itself. For instance, your 12 W remote device might draw 14 W at the wall, with the remaining 2 W heating up your crawlspace. The proposed 70 W IEEE 802.3bt standard can put as much as 30 W of heat into the wires.
The bigger problem is typically insufficient power. The 802.4af PoE standard maximum power output is below 15.4 W (13 W delivered), which is enough to provide power for most networking devices. For higher power consumption devices, such as network PTZ cameras, this isn’t the case.
Although maximum power supply is specified in the standards, having a supply that supplied more power is necessary will not affect the performance of the device. The device will draw as much current as necessary to operate, so there is no risk of overload, just hot wires.
So PoE isn’t without its tradeoffs. Nevertheless, there’s certainly a lot of advantages to accepting PoE for devices, and of course we welcome a world with fewer wires. It’s fantastic for routers, phones, and their friends. But when your power-hungry devices are keeping you warm at night, it’s probably time to plug them into the wall.
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).