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 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).
We’ve previously covered the Waveshare LAN8720 board for anyone who’s interested in the ins and outs of getting their ESP32 talking Ethernet. If you’re wondering how you can put PoE to work for you, our very own [Jonathan Bennett] has been showing off his home Raspberry Pi infrastructure which makes extensive use of the new PoE hat.
Let’s not forget a Hackaday project with ESP32 and POE:
https://hackaday.com/2018/08/19/wiring-the-esp-32-to-ethernet/
and also this simpler and cheaper ESP32-POE board from Olimex:
https://olimex.wordpress.com/2018/09/06/esp32-poe-open-source-hardware-iot-development-board-with-wifi-ble-100mb-ethernet-with-802-3-poe-is-in-stock/
I mean those projects are cool. But this project is actually a hack.
Another cheap option would be using a RT9400 5V POE PD power module. And as a bonus there’s no need to tinker with the resisters to obtain 5V.
Tthe cost of the RT9400 it’s cheaper to buy a ready built module off ebay with a pass through RJ45’s and a 5Vdc barrel conenctor.
The olimex module looks fantastic. All the bits, small board, ready to rock.
Shame the original article didn’t have a link to his PoE board for €2 as that’s a good price.
You can often change the PoE class which can help with power budget with some switches.
Especially for some CCTV manufactures that use class 0 for everything, their products just need a resister swap for the POE driver to make them class 1 or 2 – typically low wattage devices.
Be careful, these modules are often not galvanically isolated. This is not required if you have no other io to the world, like an IP camera, but very recommended otherwise. The potential relative to earth of PoE is not specified and many devices ground the positive side, putting -48V on the negative lead.
-48V but floating. If you plug something that’s not powered by the ESP32, then it’s likely galvanically isolated so it’s also floating (typically via a transformer somehow). So, that’s not a real issue by itself.
POE use transformers too, so the 48V difference is still floating compared to main AC voltage.
There are a lot of POE options available here: https://www.digikey.com/products/en/power-supplies-external-internal-off-board/power-over-ethernet-poe/138?k=Globtek
They make Poe PD as well: https://en.globtek.com/power-over-ethernet/
ESP32-POE has no galvano isolation from Ethernet’s power supply, when you program the board via the micro USB connector the Ethernet cable should be disconnected (if you have power over the Ethernet cable)! This is a helpful site about ethernet info. https://zappedia.com/wifi-to-ethernet-bridge/