Arduino external power wont start script

Hello, i have working setup based on Arduino UNO + ethernet shield sensors: 2x DHT22, BMP180,LDR,1x relay. Its is working while powered by USB from my PC. But if i try to switch power supply to other source like 12V adapter or 5V adapter (from USB) it LEDs light up but wont start script seems like.
What i try.

is something wrong in my code that need PC to start?
Any help please? if so then detailed please im a bit newbee :slight_smile:

What is the AMP rating for the 12V adapter?

Also make sure the centre pin of the adapter is the positive terminal.

Disconnect all sensors (while power is OFF), and then try just with the Arduino and Ethernet shield only.
If that seems to be ok, then slowly add one sensor at a time to see if there is a specific sensor that is causing you problems.

Only connect and disconnect sensors while the power is OFF.
Make the changes, and then power back ON.


12V is 1.5A
5V is 1.8A

yes center pin on 12V adapter is " + " i double check that.
I try just with arduino and ethernet shield but no luck i can see on my router that it have IP adress but it wont get online on cayenne so i think something is wrong cuz powering on PC it working nice.
I can see LEDs on ethernet shield are all blinking if i connect it to PC but they are OFF if i connect it to external power.
what else i can do pelase?

EDIT: i just find out that if i push RESET button on ethernet shield then its working. Any idea why i have to push reset button?

Check out this thread Arduino status LED

Looks like putting a delay in the setup script will fix the issue. I haven’t had this problem so I can’t confirm.