Is there a drop in voltage with each shield stacked?
I have a relay shield that powers up from the Arduino UNO, however it has an Xbee socket in which I've dropped a WiFly module. The Module does not power up, unless I move the AC power cord to the AC power socket on the relay shield.
The WiFly module needs 3.3v, and when I test the voltage at the input, it reads 2.3v when powered from the Arduino.
So, long story short: I may just have to use an Xbee shield and stack the relay shield on top. But if there's going to be a drop in voltage that causes one or the other to not operate, then I need to seek an alternative solution.