Omega PoE Dock

Eric Walker

@Scott-G

I might be interested. Depends on how testing goes

Karsten Middelbeck

@Scott-G / @Eric-Walker
me too

Scott G

Woohoo! It works!
Working board

A few more images at https://github.com/zeroping/OmegaPoE.

Known issues to work on:

I got one resistor wrong (560 kohm != 560 ohm)
I need a pull-down on the line that enables the 12V output - right now, it's on at boot
The flyback converter has some instability that I don't like, and it happens to be at ~16 kHz, which means you can hear it. I want to get to the bottom of that.
I want to test it with some stacking headers, rather than direct-soldering like the first one
I want to see if I can modify a devicetree to set up the Ethernet LEDs and tactile switch correctly

But hey, I now have the silliest Ethernet-controlled light:

https://photos.app.goo.gl/YS3vjE3wA9x9WqXG7

peanut

@Scott-G Nice work!

Can you elaborate at all on your ethernet magjack LEDs? Am I correct to assume that they're functioning properly for 'link' and 'data'? How is that set up & configured on the Onion?

Scott G

@peanut Oh, they're not connected in any fancy way at all. Since the Omega has the PHY, and since there's no broken-out pins specifically for the LEDs, I wired them up to GPIO15 and GPIO16. They function in that I can light them up by flipping them high as GPIO's, but I haven't gone farther than that yet.

My understanding is that I can tweak the device tree a bit to say "No, this isn't a GPIO pin, it's an LED that is controlled by a GPIO" and then "This isn't just an LED, it's an LED that needs to be connected to an LED trigger that comes from the eth0 link status". The kernel handles it from there.

There are LED's in many routers connected in the same way, it's just a matter of messing with it, and since the DTB appears to be baked into the firmware, I think that means rebuilding the firmware. Pretty low on the list of things to do at the moment.

In case you're wondering, there are two other LEDs. One is just a general-purpose indicator. The other comes on when the 12V output MOSFET is turned on. I left that one unpopulated, but I had a little room there, and wanted to play with a reverse-mounted LED shining through the FR-4 circuit board. If you look carefully, there's text in the layers of the board, which should get silhouetted by the LED.

Place on Github that has schematic PDF (and I don't know why I can't direct-link to the PDF)

peanut

@Scott-G Thanks for the feedback. I'd love to have the LEDs tied deep in to the kernel for 'link' and 'data' but I agree it'd be a lot of work. Neat project, thanks for sharing.

Scott G

Alright, just a little more of a status update:

The boards are working great! The 12V output works for running ~12 watts of strip LED, and the Omega can control it as expected. The 5V and 3.3V lines look great, even with some load, and the Omega's running without any issues. The whole thing is even pretty efficient - with a strip of LEDs, the Omega is putting out more heat than the converter.

There was a bit of a hiccup where I failed to recalculate a resistor value when I scaled the design from 3.3V output to 12V output. That was throwing the compensation loop out of whack, causing the 16 KHz ringing. After a bit of learning about feedback compensation and some circuit modeling, I calculated the correct value, and it's much happier now - no more audible whine, no more 16 KHz ripple in the 12V line. I'm now willing to declare that this design works!

I've even fixed the rest of my boards. Aside from the first one, which gave it's life for that resistor value fix, the other three work great.

I'm eager to go make something cool with this set up, but I know I got some people interested in a group buy. If I'm going to make that happen, I have a few questions for everyone:

I've soldered the Omega down to my boards, but it should also be possible to put 2mm headers under them. Digikey is currently out of stock of the headers that are known to work, but I have some alternatives coming in a few days. The headers are only a few bucks, and only add ~4mmm of height. How many people would prefer to solder their Omega's down permanently?
There's always going to be some ripple in the 12V line when it's under full 15W load - how much ripple is acceptable to you? I'm aiming for <150 mV, but I'm going to have to add a capacitor to get that. Am I the only one who cares? I might just leave an unpopulated pad for people to add a capacitor if they need it.
We could save a few bucks if we decided
I have the 12V output header controlled by a MOSFET, controlled by a GPIO. That GPIO, however, floats on startup, causing the 12V output header to be unpredictable. I want to add a resistor to hold it either high or low during power-up. So, 12V on by default, or off?
If I run a group buy of these, how many are people interested in? They get cheaper the more that I order at once. $100 for 1, $78 for 4, $65@10, $60@40, $45@100 (approximate)... What kind of price range would people be interested in? How many?

P.S.: If anyone who works for Onion is reading, and wants to order and sell these so that I don't have to, that would be great! I'd love for my design to be the official PoE dock, and I wouldn't mind avoiding the trouble of running a group buy.

Scott G

@peanut I got the Ethernet jack LEDs working.
relevant thread here

The specific bit of device-tree magic was to add my new gpio-leds:

gpio-leds {
	compatible = "gpio-leds";
	system_led: system {
		gpios = <&gpio1 12 GPIO_ACTIVE_LOW>;
	};
       user_led: user {
		gpios = <&gpio0 0x11 GPIO_ACTIVE_LOW>;
	};
       eth_y_led: eth_y_led {
		gpios = <&gpio0 0x10 GPIO_ACTIVE_HIGH>;
	};
       eth_g_led: eth_g_led {
		gpios = <&gpio0 0x0F GPIO_ACTIVE_HIGH>;
	};
};

Note that they're on GPIO0.

And something like this:

echo netdev > /sys/class/leds/eth_y_led/trigger
echo eth0 >/sys/class/leds/eth_y_led/device_name
echo "link tx rx" >/sys/class/leds/eth_y_led/mode
echo 20 >/sys/class/leds/eth_y_led/interval

That said, it wasn't really worth it

After I got it working, I realized that the only thing it could tell me is that there were packets. The most important part of link lights is usually to know that there's link, but it's pretty unusual (but not impossible) to get Power over Ethernet without also getting, well, Ethernet. This means that on my PoE board, the Ethernet link light is only very slightly different than a power LED, which we already have. And until I get default values into the device tree, it doesn't come up until I turn it on from userspace anyways.

Still, it's nice to know how to turn GPIOs into LEDs, allowing a wide range of triggers. If this thing were in a box, I might use those ethernal Ethernet link LEDs as a heartbeat, or as an disk activity indicator.

brolly759

I am building a Hub that supports POE as well. The circuit I am using supports 12-48v DC (dont want to deal with diode rectifier for AC) POE injectors. I am actually using Ubiquity as one of the POE testers.

You have a lot more passive components than I do. Mine only uses 12 BOM line items. (14) total. Maybe because my Ethernet Jack has the Harmonics built in. Either way, good work.

Scott G

@brolly759 I'm curious to see your design - I think mine is a bit overkill.

I opted for up to 15W power, and I wanted a 12V line, meaning I have a 3.3V, a 5V, and a 12V converter. I also wanted to do electrical isolation, as I think you're supposed to for IEEE 802.3af devices that can come into contact with a person. The electrical isolation means the giant flyback transformer, as well as optoisolation and the associated passives to (hopefully) filter the opto feedback loop.

That said, yeah, it ends up being expensive. It's still working well though, and I think I'll get more boards assembled for my own use at some point.

I've been impressed by how much cheaper the RJ45 jacks with integrated magnetics have gotten. There are even some (harder to find) with built-in rectifier diodes, which saves even more components.

Fikret FiDe

I follow your project. It looks very well.

Anton Pryima

Hello @Scott-G any news on this project?

brolly759

@Scott-G
I am using Passive POE for my project.