[Noisebridge-discuss] arduino+wave shield+external power supply issue

[Andy Isaacson]

On Sun, May 16, 2010 at 10:20:47AM -0700, Michael Shiloh wrote:
> he's been using usb power while developing, but now it's time to switch 
> to external power.
> 
> as soon as he plugs in his 12VDC external power supply, the program 
> stops working as it should have.
> 
> if we re-attach the usb cable to get debugging messages, we get 
> gibberish, as if the baud rate is off. the length of the messages and 
> the timing is about right though.
> 
> any ideas? i've never used the waveshield before but i can't believe it 
> cares about the input power to arduino. by my quick glance it has its 
> own regulator, but i didn't actually find the schematic (a pointer to 
> this would be most helpful).

That's odd, I can't explain the apparent baud rate issues.

Does he have a Waveshield 1.0 or 1.1 ?  The 1.1 has some significant
improvements (compatability with more SD cards primarily) but I don't
think they should affect this problem.

I wasn't able to find the Waveshield1.1 schematic PNG on adafruit.com,
so I asked someone to render a copy from the Eagle .scm file.  The
rendering is up at
http://web.hexapodia.org/~adi/tmp/waveshield11.png

The Waveshield has a 3.3v regulator (IC1) since SD cards are not 5V
compatible.  If your 5V supply is out of spec, that would probably
explain the issues you're seeing.  I'd meter out the 12V input and the
5V supply.

-andy