A lot of work done today. I received the outdoor Ethernet cable that will supply the Odroid with both network conductivity as well as backup power. With my temporary setup I simply allow the cable to lay across the roof, but for the permanent setup I wanted something better. I found a style of Christmas light clips that are designed to hold strings of light to the roof by clipping to shingles. They are just a simple plastic clip and seemed to be exactly what I needed for neatly fasten the Ethernet cable. Turns out the clips I ordered are just the perfect size for the diameter of the Ethernet cable. Cheap, simple, and effective.
In the morning I ran the Ethernet cable and along the roof ridge, down along a vent pipe, along the garage roof, then paired it up with some coaxial cable down the side of the house, and finally into the house. For the run into the house I found the air conditioner compressor lines had a large hole that had been filled in with caulk. There was plenty of room in the caulk seal for my Ethernet cable, so I drilled a hole and pulled the cable through. After inspection I could see the black cable stood out against the white house and gray shingles. So I grabbed a can of white spray paint and a large piece of plastic. After covering an area of the roof with the plastic and placing the Ethernet cable on top, I painted the cable white. It took a bit of time, but now is only noticeable if you are looking for it. The cable has the added benefit of being located on the back side of the house, and only from a small area across the street can you see the cable at all. With a discrete run, and a caulked entry point into the house I think both the neighborhood and the landlord will not object to this cable's presents.
With the cable run it was time to test performance to the Odroid. The Ethernet cable is a really cheap outdoor Cat 6 cable I read many mixed reviews about. However, it was about half the price of all the others. Since the cable was never going to have a large network load (this is a web server that only has a couple megabits/sec to contend with) I figured cheap was worth a shot. I might have attempted my next test before I installed the cable on the roof and painted it. Alas, I didn't.
With the Odroid wired up for Power of Ethernet (PoE) I took setup to the roof. It consists of the Odroid, a 12 VDC to 5 VDC swithing power supply, and a PoE breakout cable. I spent a bit of time in the basement soldering together the pieces with a nice heat shrink covers over all the solder joints and had the setup looking pretty. Everything worked in the basement and it was off to the roof. There I plugged in the Odroid and... it didn't work. The red power LED was light, and the blue status LED blinked twice, but after that: nothing.
So it was time to trace down why things were not working. I started by bringing an external power supply. That did work, and I was able to get a network connection. I thought maybe the switching power supply was introducing noise into the Ethernet signal and tried comping a ferrite bead around the cable. That had no effect. I brought the setup back to the basement and tested the setup with an other 100 foot run of cable. But this cable functioned just fine. So the length of the cable was not the issue. However, the gauge of wire used in my cheap outdoor cable might be an issue. The long run of Ethernet cable might be causing too much resistance for the current draw. With my new power supply I could test this.
The setup was to use my power supply in a current limiting mode and see if I could reproduce the symptoms I saw on the roof. Sure enough I was able to see that if the Odroid was unable to get the necessary current it would function up until it tried to switch on the Ethernet port. This was just after the two flashes of the blue LED. In fact, at the very moment my power supply went into current limit, the red LED on the Odroid flash off briefly. On the oscilloscope I could see the power sage for about 100 ms.
My first solution attempt was to add a capacitor before on the 12 volt side to see if maybe spikes in current were knocking out the system. So I cut up all the nice heat shrink I installed to run a test. I was able to setup a situation with my power supply were a large capacitor did allow the Odroid to boot when it otherwise could not without the capacitor. However on the roof this did not help. I tried placing the capacitor on the 5 volt side, and adding more capacitance. No luck. I could either not supply enough capacitance, or the 100 foot run of cable simply could not handle the current.
Thinking the average current might be the problem, I decided to increase the PoE voltage. I had purchased a cheap 12 volt supply that was basically a cell phone charger but at the higher voltage. However, I had a bench power supply and I already knew the switching DC-DC converter could handle up to 20 volts with no problem. So I decided to power the PoE from my bench supply at a higher voltage to see if that helped. There was one problem though. My Ethernet hub is not near my bench power supply, and I didn't have a good way to bring the two together. My solution was far from elegant, but it was functional. I hooked my lab supply to an extension cord using alligator clips from the supply to the extension cord prongs. On the other side I used paper clips jammed into the outlets and more alligator clips to direct the power into the PoE adapter. Ugly, but functional enough for a test.
The results were a functional Odroid on the roof. While I started at 20 volts I found I all I needed was 14 volts—12 volts just wasn't enough to get the total wattage necessary to the roof. It was not my cheap power supply either. My bench supply could provide plenty of amperage, much more than the cheap 12 volt supply. The cheap Ethernet cable has smaller gauge wire than is allowed for category 6 cable and I had already read that complaint in the review feedback for the cable. I just didn't figure it was going to be an issue like it was.
Nonetheless, I have a solution. I will have to select a new PoE power supply, and it will be harder to find one at this odd voltage. However, the Ethernet cable will function and the PoE will only be used when the setup doesn't have enough stored solar energy to run. It has been a long trying day, but I found a solution.