Post
by cef » Thu May 17, 2012 9:51 pm
Hi anas_ali,
Simply put, if you buy any ethernet shield without a PoE regulator, then you will not be able to power the shield/arduino over the ethernet cable, and will have to power it via other means (eg: usb, via the power connector on the arduino, etc).
With something like the Freetronics Ethernet shield, the EtherTen or the EtherMega boards, which have a connector for a PoE regulator, you could install one at a later date, should you change your mind and want to power your project using a PoE switch or PoE injector (via the the ethernet cable). Same should apply to any other Ethernet shield that allows you to add a PoE regulator.
If you do want to add PoE to your project later on, make sure you leave enough room for the PoE regulator to fit on the shield when designing/making your project.
Notes:
1) The PoE regulators can only provide a limited amount of current (802.3af specifies a max guaranteed of 12.95W of usable power, some of which gets lost in the conversion process), so if you have project that draws a lot of current (eg: say more than 500mA) it is probably worth it to run a dedicated supply.
2) I would not guarantee that the pinout of the PoE regulator from Freetronics would work on any other brand Ethernet shield, and vice versa (any brand PoE regulator with a Freetronics shield). If someone wants to go down this path, feel free to ask about the specific combination of PoE regulator and shield.