Power over Ethernet (PoE)

I know this topic has come up a few times and this product has been recommended previously https://www.amazon.com/gp/product/B07CNKX14C/ which is 5V/2.4A.

However the Raspberry Pi 4 Model B requires a 5.1V, 3A (15.3W) power supply. To this end I purchased a (1) REVODATA https://www.amazon.co.uk/REVODATA-Splitter-IEEE802-3af-Adaptive-TYPEC0504G/dp/B0CHW5K5F4/ which is 5V/4A and a (2) PTZlink https://www.amazon.co.uk/Injector-PTZlink-Ethernet-1000Mbps-Compliant/dp/B09FHLGVZ1/ Both are IEEE 802.3af 802.3at.

Alas this combination doesn’t work, power is supplied and the Shake is happy but no Ethernet link is established. I say the Shake is happy because if I power it from the PoE and plug in a direct network cable then the Ethernet port Tx/Rx lights spring into action and all is well, whereas previously the lights were unlit. However I have seen for a brief 0.5 seconds the ports lights come to life and the Shake responds to pings but then the lights go dark. Have of course tried various cables, different lengths and Cat 5E / 6E.

Don’t have the spares to try and determine if it’s a sender, receiver or both problem.

Anyone have a working Raspberry Pi 4 Model B and RSBOOM PoE solution?

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Hello Hadders

You can supply 12 V by Ethernet and near RS you put a pasibe inyector with a DC-DC step down converter to 5.1 V.
(REF: Structural health monitoring of South America’s first 6-Story experimental light-frame timber-building by using a low-cost RaspberryShake seismic instrumentation, Engineering Structures, Volumen 275, Part B, January 2023)

Be careful with the thickness of the 5 V cables, they are usually of a section that does not support 3A, causing the RS to report power problem in /var/log/kern.log



This is very interesting, Hadders; keep us posted on your progress!

I think you may be the first (or one of the first) Shakers testing a PoE implementation with a Pi4 board, so what you find will be extremely useful to the community.

That looks like it should work. I would spend a bit of time finding out which part is not working (faulty).
It sounds as though you have validated that the power works correctly by directly connecting an ethernet cable, so it sounds like a problem with the ethernet connectivity in one or other of the devices.

Maybe try normal power then connect your known good and working ethernet cable into part 1 and then into the R-Pi - still works? Then that component is probably ok - if not, get Amazon to exchange it.

If all is ok with (1), then connect your ethernet cable to part 2, and from part 2 to the R-Pi (without powering it - it shouldn’t need power for this test). Again if it works, it is probably ok, if not - Amazon exchang would be the next step.

Last step would be to connect (1) to (2) and see if there is connectivity - if each part worked, this should work. Assuming it does, apply power (no need to load it). Still works? Apply a load (Another R-Pi or similar).

Somewhere along this chain of testing you should be able to isolate the defective part …


Thanks all.

@Alejandro Very useful info. I checked over /var/log/kern.log (and /var/log/kern.log.1, etc) but nothing there pointed to a problem. Will keep in mind conductor thickness. If I can’t get anywhere with an IEEE 802.3af 802.3at solution will look further at your suggestion (page 9) https://repositorio.uchile.cl/xmlui/bitstream/handle/2250/188853/Structural-health-monitoring-of-South-America´s-first-6-story-experimental-light-frame-timber-building.pdf

@PhilipPeake Tried some of these “If all is ok with (1), then connect your ethernet cable to part 2, and from part 2 to the R-Pi (without powering it - it shouldn’t need power for this test). Again if it works, it is probably ok, if not - Amazon exchang would be the next step.” Unfortunately I couldn’t get a signal through without power which either means it needs power to passively pass the signal or this is a faulty unit.

Lots of unknowns to juggle & it could be both units are faulty or just not compatible with each other.

Shortest injector to splitter cable I tried was a 0.5m Cat 6 (possibly Cat 6a).

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Managed to find a computer with a console and ability to connect over Ethernet.

To cut a long story short the problem seems to be with our old friend “auto-negotiation” and / or duplex with the PTZlink injector, the REVODATA splitter seems to behave fine.

I worked with ‘ethtool’ on the console computer. On the Shake ‘ethtool’ is not installed, only ‘mii-tool’. Not sure if it’s a good idea to install anything on the Shake?

Have yet to work out exactly what’s going on but have ruled out the router, cables & type / lengths. Am beginning to think the PTZlink isn’t suitable or is just faulty.

Considered adding in a ‘100baseT Full’ line somewhere on the Shake using mii-tool, however I’ve seen the link drop during my tests (like when writing this message!) which again points to a problem with the injector so this might not the best fix.

Parking some notes here as an aide-mémoire. Note the ‘Link partner advertised link mode’ (PTZlink injector) doesn’t even offer 1000baseT even though it is sold as a gigabit device.

$ sudo ethtool -s enxb6d397fe3496 advertise 0x008

0x001       10baseT Half
0x002       10baseT Full
0x004       100baseT Half
0x008       100baseT Full
0x010       1000baseT Half       (not supported by IEEE standards)
0x020       1000baseT Full
$ ethtool enxb6d397fe3496 ; echo ; echo -n "Link speed: " ; cat /sys/class/net/enxb6d397fe3496/speed 

Settings for enxb6d397fe3496:
	Supported ports: [ TP	 MII ]
	Supported link modes:   10baseT/Half 10baseT/Full
	                        100baseT/Half 100baseT/Full
	                        1000baseT/Half 1000baseT/Full
	Supported pause frame use: No
	Supports auto-negotiation: Yes
	Supported FEC modes: Not reported
	Advertised link modes:  100baseT/Full
	Advertised pause frame use: No
	Advertised auto-negotiation: Yes
	Advertised FEC modes: Not reported
	Link partner advertised link modes:  10baseT/Half 10baseT/Full
	                                     100baseT/Half 100baseT/Full
	Link partner advertised pause frame use: No
	Link partner advertised auto-negotiation: Yes
	Link partner advertised FEC modes: Not reported
	Speed: 100Mb/s
	Duplex: Full
	Auto-negotiation: on
	Port: MII
	Transceiver: internal
netlink error: Operation not permitted
        Current message level: 0x00000007 (7)
                               drv probe link
	Link detected: yes

Link speed: 100

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Interesting… I have to admit I was thinking of both components being passive. At least as far as the ethernet connectivity is concerned.

Having been bitten too many times by auto-negotiation, I have to admit that I generally fix the speeds of most of my things - particularly where any appreciable cable runs are involved. No matter what quality cable.

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Hello Hadders

I had communications problems between one router and an RS4D. The problem was that the router used RJ45 pinout T-568A (Straight) and the RS4D needed with T-568B (crossover).
It could be the same problem



@PhilipPeake A learning experience for me, appreciate your comments.

@Alejandro Thank you for this, a great thought. Fortunately all wired correctly on my side but useful to have the wiring standard refs.

Have come up with resolution which I’ll describe in a separate ‘Solution’ message.

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Convinced I had been sent a rubbish or faulty PoE injector I purchased a TP-LINK TL-POE160S https://www.amazon.co.uk/TL-PoE160S-Injector-Supplies-Wall-Mount-Distance/dp/B08LQP8CYD/ which immediately worked and at 1000baseT/Full. It’s also a much more professionally packaged product, sealed with manual and ethernet cable.

Link partner advertised link modes:
10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full

Amazon sent a Ver: 2.0 unit whereas according to TL-POE160S | PoE+ Injector | TP-Link United Kingdom the latest is Ver: 2.6.

I only installed it this morning but the RSBOOM and Raspberry Pi 4 Model B are powered and networked. Occasionally there is small packt loss, about 0.1% which I don’t think was there previously but this could also be because I’ve started dabbling with rsudp and added sending to a Datacast host (the “Shake live real-time data streaming and archived data access” downtime did have an advantage giving me the push I needed). I’ll keep an eye on the whole system and see how it behaves over the next few weeks. I notice sometimes ping times go up to 271 ms from say 5 ms so one possibility could be the unit is jumping between IEEE 802.3af 802.3at if the power consumption is on the borderline. It could also be because the injector is a Ver: 2.0 rather than Ver: 2.6 or possibly because this is just what PoE does.

So now I have my router and distant RSBOOM on the same UPS. Happy days :smiley: !


REVODATA splitter https://www.amazon.co.uk/REVODATA-Splitter-IEEE802-3af-Adaptive-TYPEC0504G/dp/B0CHW5K5F4/ (5V/4A) and TP-LINK TL-POE160S https://www.amazon.co.uk/TL-PoE160S-Injector-Supplies-Wall-Mount-Distance/dp/B08LQP8CYD/ provide power and 1000baseT/Full but I have noticed occassional insignificant packet loss which might not be related.

Avoid PTZlink style PoE injectors, however my unit could have been faulty.