https://www.hackster.io/news/pixpoe-putting-plenty-of-pixels-wherever-you-can-plumb-some-cat5-9a8f24c3b485

http://albert-david.blogspot.com/2019/09/poor-mans-poe-for-raspberry-pi-3-under-2.html

https://albert-david.blogspot.com/2019/09/poor-mans-poe-for-raspberry-pi-3-under-2.html?m=1

While most projects we see with the ESP32 make use of its considerable wireless capabilities, the chip can be connected to the wired network easily enough should you have the desire to do so. [Steve] liked the idea of putting his ESP32s on the wired network, but found the need for a secondary power connection burdensome. So he took it upon himself to modify some cheap Power Over Ethernet (PoE) hardware and create a single-cable solution (Google Translate).

[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 is was using to generate the nominal 12 V output.

https://geeks-r-us.de/2019/02/03/esp32-mit-poe-fuer-unter-10e/
https://translate.google.com/translate?sl=auto&tl=en&u=https%3A%2F%2Fgeeks-r-us.de%2F2019%2F02%2F03%2Fesp32-mit-poe-fuer-unter-10e%2F

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).

[Jason Gin] has taken an old, cheap passive PoE splitter and upgraded it to be 802.3af compatible (an active device).

Upgrading a passive Power over Ethernet splitter with 802.3af compatibility
https://ripitapart.com/2018/08/22/upgrading-a-passive-power-over-ethernet-splitter-with-802-3af-compatibility/

The DWL-P200 is a near-ideal candidate for conversion to 802.3af/at (I’ll call it “active PoE” from now on) since it already uses 48 volts for power – all it really needs is an active PoE-compatible front-end which requires an Ethernet isolation transformer, two diode bridges, a TVS (transient voltage suppression) diode, a 802.3af PD controller chip (and a partridge in a pear tree?). Easy enough, right… right?

The actual front-end was built as two separate boards: the first was the power input board; the second was the 802.3af active PoE PD controller, which had its own construction considerations

The power input board is pretty simple and was comprised of two Bourns CD-HD201 60-volt Schottky diode bridges and a SMAJ58A 58-volt TVS surge suppression diode to help overcome voltage spikes that can occur when a cable is unplugged due to the inductance in the cable itself.

The second board is the PoE PD controller, which is responsible for negotiating with the 802.3af/at PSE controller at the other end of the cable. I used the Texas Instruments TPS2378 PoE PD controller, which was meant for 802.3at Class 4 (25.5 watts maximum) but I’m only using it for 802.3af Class 0 (up to 12.95 watts).

With the active PoE upgrades installed, the splitter now works with 802.3af, 802.3at and passive 48 volt PoE power sources. However, the internal construction of the splitter means it only supports 10/100 Mbps Ethernet. Additionally, I find that the board gets very hot under full load