I am connecting Arduino Mega to network for communication with MQTT broker.
I tried two different ethernet modules (both small board, not a whole shield) - WizNet5100 (funduino) and a ENC28J module.
I have 2 pieces of each module and 3 Arduino Mega compatible boards (tried different combinations).
On one of the 3 Arduino mega board it works OK with ENC28J. On other two boards that I have and have tried I have the same problem with both WizNet & ENC modules.
If Arduino is connected to USB (To computer or USB Power Adapter) it works OK
If Arduino is connected to 12V power supply (tried two different switching PS) trough jack socket, then after a minute the connection crashes.
I found out that the voltage on the 5V pin of Arduino slowly drops under 4V even to 3.5V and that's why everything crashes.
Furthermore the voltage regulator on the Arduino (near to jack socket) gets very hot (I cannot hold the finger on) - so I suppose this is the problem.
After I have installed the heatsink on the regulator, the connection is quite stable and doesn't crash. But this doesn't feel to be a stable solution for a long-live system.
Is this normal? Do this modules draw so much current? I only one DS2018 to measure temperature and send it to MQTT - NO other peripherials connected to Arduino. The behaviour is the same even if I do not connect the network cable.
Do I have to power this modules separately? Any suggestions?