Power Over Data

Delivering power over wired data lines has been one of the most obvious extension to many legacy protocols. It is hard to comprehend why many of these protocols did not have the power option from the beginning, requiring the connected devices to be fed power over a separate line (and a separate cable). Less cables is always good.

My own journey with cutting power cables started about 40 years ago when I designed my first commercial product - a software protection dongle. The dongle was using the PC printer port for communication. Unfortunately the printer port never had power lines in it, but I managed to harvest sufficient energy from the data lines. 

Next in line was USB, and the inclusion of power was a very significant (if not the most significant) contributor to the success of the standard. Now with the Power Delivery (USB-PD) capable of carrying up to 240W of power, the PD is the king of power-over-data standards.

HDMI is the one that really failed to do this properly. There is a 5V power line in the HDMI cable, but it is only powered from the source (sender) side. This for example helps building long and thin fiber optic HDMI cables, where the sender (such as a laptop computer) powers the electronic-to-optical conversion chips which sit inside the HDMI plug. This is why the fiber HDMI cables are not reversible - they only work when the right plug is plugged to the sender socket. Failure to deliver power from the receiver side really killed the concept of TV dongles, as they always must be powered from a USB port or an external power supply. 

Power-over-Ethernet (PoE) is an another nicely done standard. With several evolutions (trying to power full lighting fixtures with the Ethernet cable) it is well established and works particularly well for devices drawing moderate amounts of power. Such as Ethernet switches, cameras, and other small appliances. There is something magical about PoE-powered LAN switches, as you simply plug them in a chain using only the data cables and they lit up and also provide power down the chain. PoE cameras use single cables for power and data. Plus many small embedded computers have the PoE option - from Raspberry PI to Home Assistant Yellow and even smaller ESP32. The beauty of PoE are the safe voltage/power levels. At home I have multiple PoE switches powering several LAN segments and in the end variety of those small things. When leaving home I can hit the power master-switch (for safety) and the PoE-powered devices continue to operate.

Finally, on the commercial lighting side, there is DALI2, a 2-wire digital bus with the option to power devices connected to the bus, such as sensors and controllers. While DALI2 enabled power over the bus, D4i, the subset of the DALI standard has made the bus power mandatory. This has radically simplified connecting DALI sensor/controllers (in particular Bluetooth NLC sensor/controllers) to D4i drivers. Just two wires for power and data.