6 years, 8 months ago.

lpc1768 with rj45

Hi all, I need to connect my lpc1768 board to internet. I used the following tutorial to connect ethernet cable to my board :


I connected one end of ethenet cable to POE enabled switch and the other stripped end to the board using green and orange wires of the ethernet cable.

I plugged the usb cable to board and the board blown up :/

I have spare board, can any one help me out how can i made the connection

1 Answer

6 years, 8 months ago.

Hi zain,

Don't subject the second board in the same manner, or it too will fry!

Those instructions might be ok for the purpose they were intended - from a notebook to an mbed, but not for what you want to do.

Power Sourcing Equipment (PSE), like a switch provide power down the cable, using different pairs of wires (depending on the rating of the switch). I'm no expert on POE, but in principle, the PSE tries to sense if the device at the other end of the cable is a PD (Powered Device). If the PSE determines that it driving a PE, it will then apply a steady voltage. This voltage can be up to 57v.

A non-POE device (like the mbed) would typically use magnetics (a transformer) between the micro and the network cable. This transformer isolates the mbed from the high voltage from a PSE, and when properly wired, it draws actually wastes no power from the PSE.

In all likelihood, that initial attempt of the PSE to sense what was on the end toasted the mbed.

Where to go from here?

These are not endorsements from experience, just scraping links that others have shared. I designed my own SmartBoard Baseboard.

Accepted Answer

so I even shouldnt wire my other mbed with the non POE switch ?? Well I have ordered cool components breakout. Thanks alot for your suuggestions

posted by zain aftab 28 Nov 2014

With a non POE switch it might be just fine - yet I would not recommend that configuration. If your bench is anything like mine, there are several ports to choose from and the cables of course all look the same. Some are POE, and some not. The first lesson was unfortunately expensive - I'd hate for you to repeat it accidentally.

posted by David Smart 28 Nov 2014