shields interfering with one another?

Hi, so I'm an arduino newbie. I'm working on a project that involves two things connected to the arduino Uno: 1) a simple electret mic shield, with three wires: +V, gnd, and audio signal; 2) an addressable LED strip (WS2801 chips) with four wires: +5V, gnd, clock, and data. In short, I'm having sounds picked up by the mic control LEDs on the strip.

I encountered trouble when I tried to get these two externals to work together. I initially thought I could use the +5V pin on the arduino board to power both the LED strip and the mic shield; similarly, I assumed that the LED strip and the mic could share the same ground. However, when I did this, the signal I was reading from the audio shield seemed all "wonky".

I was able to get things to work as desired by hooking the +V wire of the LED strip to the +5V pin of the arduino, the gnd wire to one GND pin on the arduino, and then hooking the =V wire of the mic shield to the +3.3V pin of the arduino, and the gnd wire of the mic shield to a separate GND pin on the arduino.

My question is: why did I have to do it this way? Why couldn't I power the LED strip and the mic shield from the same +V and GND pins? I don't think it's a too-much-power problem. The arduino seems happy to power the LED strip (it's not too long), and I imagine the mic shield draws almost no current. So what gives?

Have you tried measuring the devices to actually see how much current they are drawing?

No I haven't. I'll have to dig out my meter.

snapster:
hooking the =V wire of the mic shield to the +3.3V pin of the arduino, a So what gives?

Going to the 3v3 may have been a lucky stroke. You don't say where your power is coming from. Things can quickly get marginal if you are just using the USB cable and your PC can be the villain hidden in plain sight.......