Stacked shield doesn't have enough power -- dim PWR light <p>I'm stacking a <a href="http://www.seeedstudio.com/depot/bluetooth-shield-p-866.html" rel="nofollow">SeeedStudio Bluetooth Shield</a> on top of a <a href="https://www.olimex.com/Products/Duino/Shields/SHIELD-EKG-EMG/resources/SHIELD-EKG-EMG.pdf" rel="nofollow">Olimex EKG/EMG Shield</a>.</p> <p>At first, I stacked the two loading only bluetooth shield demo code and all the LEDs lit up brightly and worked fine.</p> <p>Now (having only taken a shield off and put it back on), the lower shield's (Olimex) power LED appears dim and the upper shield (Bluetooth) is not powered at all. The lower shield's power LED brightens when I remove the top shield.</p> <p>Not sure what happened here -- both shields work perfectly if they are the ONLY shield on top of the Arduino. Is there any way for me to check the output voltage coming from the lower shield (Olimex) to the higher shield (Bluetooth) with a multimeter to see if it's sufficient (3.3V)?</p>