I found that powering the Arduino Nano can be problematic in certain scenarios. Sometimes there is just no power outlet near your chosen location or you just want to keep the amount of cabling to a minimum (ideally just one going to the node). This is where Passive POE fits the bill (note: It is not perfect so your millage may vary). I really like using the screw shield for the Nano but this also limits how I can power my project. The official specification says the following:
"The Arduino Nano can be powered via the Mini-B USB connection, 6-20V unregulated external power supply (pin 30), or 5V regulated external power supply (pin 27). The power source is automatically selected to the highest voltage source."
So... I did some investigating. Image 1 represents a typical passive POE splitter. Image 2 shows the module being gutted and connected to the Nano (I just need the red and black cable).
This "idea" has worked perfectly. Now, I did come across a female 2.1mm jack adapter when I worked with CCTV systems. These things should happily "convert" the power cable from the passive POE module into two cables (power and ground) that I can just feed to the Nano. Image 3 gives you a clue of the entire setup. At the "input" end I am using a 9v power supply, passive POE splitter and 20 meter ethernet cable. At the "output" end I have a passive POE splitter that provides the RJ45 jack to the Nano ENC28J60 shield and the power male jack that goes into the female adapter (which provides Nano the juice with two wires).
Image 4 demonstrates what voltage I am getting using this setup. The good news is that It is a stable 6.64v and it does meet the official power requirements (I would also use a UPS for a full peace of mind when deploying something important in the wild). If I would place a sensor 30 meters away it would probably need a 12v power supply (voltage drop over distance = physics). As usual, your mileage may vary. On the flip side I have found an interesting shield for the Nano. It can accomodate any normal size shield that you can add to an Arduino Uno. It has a barrel jack connector for power - interesting one... So far it seems it can be only purchased from China (name: arduino nano-uno adapter).