Voltage drop after couple of seconds - Arduino broken?

Hi everyone,

The last couple of days I've been using my Arduino again. At first everything went fine, but now I'm running into some trouble I'd like some advice on.

I have an Arduino Duemilanove to which I have attached an Ethernet Shield (without SD-card slot) and a small I2C OLED display. Trying to demo my project to a friend yesterday the Arduino kept shutting down after a few seconds. I have tried different power sources, PC via USB, external adapter at different settings (4.5V, 6V, 7V). Using the external power connector I do get a power light, but my display doesn't turn on. Using power supply via USB it turns off after a few seconds... Windows doesn't recognize the USB-device in this configuration and makes the 'USB device removed' sound when the Arduino turns off.

When I remove the Ethernet shield it takes a little longer before the Arduino shuts down. Also, Windows does recognize the USB device and I'm able to upload new software.

What could be wrong and/or what tests or measurements could help determine the problem? I'm not very familiar with electronics so I'm sorry if I'm overlooking something really simple here.

Kind regards, Chris

Sounds like you're drawing too much current. USB is only good for 500mA. You haven't said what the current rating is on your external supply.

The external supply is also limited to 500mA.

Though, the odd thing is I haven't changed anything in my circuit and it has worked flawlessly for hours before... That's why I don't think it's due to drawing too much current.

Does the '328 itself get hot? Do other components feel hot?

If you write a sketch to make each IO go hi-lo-hi-lo, and connect an LED-resistor-Gnd, do all the pins work? Don't test on 0,1, that could cause you download grief for the next sketch.

I have just gotten to checking the pins and they are all fine (digital and analog).

Also, I’ve got my hands on a test power supply capable of delivering 1.9A.
I have used this to power the Arduino with Ethernet shield. The voltage didn’t drop too much, but the voltage regulator on the Ethernet shield got pretty warm.

While writing this reply I kept performing some measurements to write about, but somehow everything seems to be fine suddenly.
Long story short, without really changing anything to my circuit or program, somehow it’s now running stable again for almost 5 minutes.

Thanks for your suggestions.

My guess is that your power supply was cutting out. The USB-supply is usually run through a PTC fuse, which swells as it heats due to too much current being pulled. The swelling eventually cuts off current flow until you remove the excessive current draw, the PTC cools down, and becomes 100% operational again.

I am surprised that the USB power supply was not powerful enough to drive your Arduino, the ethernet shield, and the display. But without the benefit of a current measurement or two, it would be hard to tell just where the power is going.

That the regulator feels warm may also be a reflection of the incoming voltage - that 1.9A power supply, is it more than a 9V model?

This morning when I picked up the Arduino again it was still having the trouble described two days ago.

The power supply is a custom built one (not by myself though) with a voltage selection dial. I had it at 5V.

Have you verified the voltage?

Yes, it's 5.2V

Are you running that 5.2V thru the barrel jack connector, or directly into the 5V on the power header? The barrel jack needs ~7.5V for the regulator to work. Putting in 5.2 you will be underpowering the board.