Power supply problems when stacking shields

Hi there,

I recently put together Ovidiu Predescu's "Tiny Web Server" project and ran into some trouble powering the Arduino-Ethernet-data logger shield stack.

I'm running a standard Duemilanove, with the "official" Adafruit Ethernet shield stacked onto the output pins, with the data logger stacked on top the Ethernet. This is actually a modification of Predescu's original spec, which called for the Ethernet on top of the data logger; I didn't happen to have any extra socket headers, and so I tried squeezing the data logger down on top of the Ethernet shield to take advantage of its sockets.

The two shields have been modified as in Predescu's images.

The problem is that when I attempt to power up the whole device, it fails; none of the indicator lights on any of the boards flashes, and the serial monitor doesn't register any activity. The board seems to function fine on its own, and each shield appears to work when used separately from the other. When attempting to connect the combined devices to my MacBook, OS X throws an error complaining that the USB is drawing too much current. When programming the Arduino board separately and attempting to power the device with the standard Arduino power supply that ships from Adafruit, it fails to power on, and the indicator light on the adapter plug flashes. The board also gets fairly hot in both instances.

Are these symptoms indications that the two combined shields just draw too much current? Or could it be caused by some fault in the hardware, either as a result of my modifications, or by some other defect? Should it make a difference that I've stacked the data logger on top of the Ethernet and not vice versa? Is there something I can do to correct the problem?

Any help would be much appreciated.

URL for the web server project details:


with the "official" Adafruit Ethernet

The Adafruit shield is not the "official" design: there are some differences that might get you wrong answers, so you should make sure you identify it if you need to ask any other questions in future.

I wonder if the problem isn't a short caused by setting the datalogger board on top of the Ethernet board: that metal-shelled Ethernet connector is a serious risk if it touches the PCB above it. When I needed to stack on my Adfruit shield, I used a set of the stacking headers as "extenders" to make sure the prototyping shield was well clear of that connector.

After putting this down for a couple days, the same thing occurred to me yesterday: that one of the exposed pins on the bottom of the data logger was, in fact touching the metal housing of the Ethernet port, and this might be the source of the problem.

Putting a piece of electrical tape over the housing and placing the data logger as before appears to resolve the issue.