Issues with my 5v power circuit & Ethernet shield

Hello everyone.

I’ve designed and made my own shield for providing 5V stepped from 24V to an Arduino Mega 2560 as well as opto isolating some I/O, thread here

I’m trying to use this also in conjunction with an Arduino Ethernet Shield (see illustrations).

I understand that it’s possible and widely unproblematic (although not endorsed by Arduino) to supply regulated 5v straight to the 5v pin and bypass the onboard regulator. Does the same hold true for the Arduino Ethernet shield?

I seem to be having problems with the arrangement; it works very intermittently, but most of the time appears to cause the arrangement to continuously reset, or causes the Ethernet Shield not to work (‘FULLD’ flashes slowly, but the whole arrangement works when I remove my shield and power from USB). Testing with a multimeter seems to show a very stable 5v going into the relevant pin and appropriate continuity for all connections.

I’ve also attached a circuit diagram of my shield; which may not a master piece of electronics design but is true to the circuit so I can clarify any points that it does not!

Hi, I am having the same issue than you iguess. MEGA + ENC28J60 (Comunication issues) - General Electronics - Arduino Forum

In my case i since the Ethernet Module is 3.3v, i used a 3.3v linear regulator, and +9v for the Mega. having the same result as you.

It loose the comunication with the ethernet module after some time. The only way that i found it works, is powering my Mega from a different power source in this case. 9v wall wart common power supply 500ma. and the 3.3v from power swithching .

I am continues investigating why when it came from the same source it hang. i will follow you post for any news. and if i find something i will keep you aware of that.