Arduino Mega, Ethernet Shield,Proximity Sensor and External Power Problem

Development Tools IDE 1.x
1

Hi,

I developed a mini project to read a sensor value and send this value a sql server via ethernet shiled. I bought a screw shiled to connect sensor cable. Everything works great when i use system via USB cable whic is connected to my computer but when i plus 12V/1A wall wart adaptor there is problem. System power on but it doesn't work properly. I looked voltage values and it looked normal 5V and 3.3V of board.

Then i used a 7,5V/1A wall wart (this option is recommended at this forum) adaptor and nothing changed. Problem is such : When i use system with USB cable i measure 0V at sensor output and when i show something to sensor it gives 4,9 V (This expected). But when i use wall wart adaptor i measure 1,9 V at sensor although i don't show anything to sensor. And this value doesn't change even if show something to sensor. What can be problem? I will be crazy because of this problem.

Thanks in adance and regards

2

I read same problem with me at another forum and a guy answered such (and his answer is accepted)

The problem is that when you are using the external 9V plug pack, you are relying on the Arduino's on-board regulator to provide the 5V power supply to both the Arduino and the Ethernet shield. This regulator has very limited current capacity — much less than the 500 mA that's available from a PC's USB port — and you're overloading it.
To avoid this problem, you should use a 5V plug pack with a USB connector to power your system.

Is this answer and solution is right? Should i use an external USB wall mart adaptor? Is this unique solution? I will add and relay shiled soon. I think it can be a problem if i feed my board only with 500 mA from USB...

Regards