POE and Wired networking?

I am working on a couple of projects for Air Quality monitoring. In many of my networking systems, we use POE Ethernet. This avoids all issues with WiFi and AC power, as the central equipment can have redundant power as the customer requires.

I have not yet dug into the DIY system’s hardware to see what the possibilities are. I just wanted to toss out the idea!


For instances in the past where I needed POE power to a non POE device (like an access point that doesn’t have POE built in), I just use an adapter. Amazon is packed full of them. Alternatively if you wanted to build POE into your build, you need a step down converter from 48-55v to 5v. The adapters are so cheap that between the cost of parts and the cost of time to build it, you’d come out ahead buying the adapter.

Edit: The board you need for wired ethernet is: WT32-ETH01, but it won’t fit in the AirGradient case.

This is interesting! Why do you think it won’t fit the case? because it’s too big or because of pinouts?

Also, that board doesn’t look like it’s dealing with PoE, do you think there’s a way to work around that?

It looks like this board might do both ethernet and PoE, and should work with Arduino boards like the Airgradient:

That provides 1.5A, not sure that’s enough for the AirGradient, what’s the input power for the DIY kit? The AirGradient ONE spec talks about 2A at 5V, so maybe that’s not enough.

[Continued because Discourse doesn’t want me to post multiple links at once.]

Also, not sure it would fit better of course… The olimex is unclear about dimensions. Main page says 80 x 28 but the user manual says 98 x 28mm.

In the raspi world, there’s a bunch of options as well, for example Adafruit stocks this (56.4mm x 20.3mm x 13.2mm):

Also provides only 1.5A though.

This one is the “insulated” version that’s supposed to be larger, but looking at the specs it’s actually smaller, or at least differently shaped (56 x 14.3 x 16mm):

Their specification pins it at 2A over 5V, but the adafruit site mentions 1.8A so I’m not sure what’s up there.

Finally sparkfun has this board: (look on sparkfun dot com for product 18709 since I cannot link to it).

That also does the 1.8A nominal dance, so also unclear if has enough power. Dimensions of the main component seem to be 14x13.39x21.19mm according to the specification so maybe that’s the chip that would be needed to rewire a kit properly.

Anyways, that’s what I found in my search. I’m far from an electronics person that could pull this off right now, but maybe soon I’ll look into how this could be bolted on instead of relying on wall warts…

PoE is my favourite way to power network attached devices and yes, I do like UPSs as well.
Thanks for starting PoE ball rolling.

If I am not wrong, I think that you are describing Passive PoE and not
Active PoE. It is my understanding (and I can be wrong), that one may not need that step-down converter. Which means it could be smaller and not as hot.
Do correct me if I am wrong. However, do explain why I am wrong.

Not sure what you are asking. As a standard PoE runs at 48v (and sometimes at 24v) on the last pair of the 8 pin connector.

The first problem is that Wemos D1 does not have an ethernet port, so add a board solely for that purpose. The second problem is that no component in AirGradient is capable of accepting 48v.

If you’re talking about Active PoE in terms of a port that negotiates a voltage, the board still needs to be able to support voltages of 48v in case the source power does not support negotiation.

I don’t work for AirGradient and have no vested interest in implementing PoE, but if you’d like to give it a try, I’m sure the community would appreciate your contribution.

Thank you, Brian.
I found your explanation most illuminating.
Though I do question the decision to start with 48 volts instead of something much lower, but that is so not your fault.

The most common standard would be 48v with a max current of 350ma per port, which, converted down to 12v with no loss would theoretically be 1.28A or 1280ma.

Also, remember 23AWG conductors in a Cat 6E cable will have voltage loss over distance, so expect that the 48v starting voltage will be lower at the device, which is why the voltage is stepped down from such a high voltage.

Standard PoE (802.3af) is 48-56V at the PSE (power source equipment, usually a switch), to compensate for voltage drop along the cable run.

I wasn’t aware that PoE devices could negotiate the voltage at all; I thought the negotiation only referred to the current they are asking to consume so the PSE can decide whether it can provide that much power or not. Every PoE receiver I’ve seen expects to receive 48V and then uses a switching power supply to provide the desired output voltage.

Passive PoE is an entirely different thing and is getting pretty uncommon on off-the-shelf switches. I wouldn’t design a new device in 2024 which uses it.