[Lab] Arduino CapSense library + Shiftbrites + interference

Jean-Marc LeBlanc jeanmarc.leblanc at gmail.com
Wed Apr 13 12:44:58 EDT 2011

when running on a battery (non grounded circuit), you need to have
your hand pass between 2 tin foils where as if its get power from the
USB (grounded circuit), only one foil is required.  That is my
understanding of it.  I am not sure how you have it set up I am going
off what I ready here


"If your Launchpad isn’t grounded (ie. running from battery power),
add a second foil to ground and move your hand between them.

I’ve found that when using a small capacitor alongside the foil I see
less background noise."

Jean-Marc Le Blanc

"Do you pine for the nice days of Minix-1.1, when men were men and
wrote their own device drivers?" Linus Torvalds

On Wed, Apr 13, 2011 at 12:13 PM, Andrew O'Malley <aomalley at gmail.com> wrote:
> Hi all,
> Thanks for your replies thus far.
> @Charles, the acrylic sheet is integral to the design as it is the
> diffusing material.
> @Tom + Adam I'm going to try the tinfoil shielding tonight.
> Here's a preview of what we're working on, including pics of the inner
> electronics and renderings of the outer enclosure (the acrylic will be
> the windows):
> http://www.facebook.com/album.php?aid=289063&id=101546226937
> Cheers,
> Andrew
> On Wed, Apr 13, 2011 at 12:07 PM, Charles Richer
> <charles.richer at gmail.com> wrote:
>> Silly question does it make a difference whether you have the acrylic sheet
>> or not.
>> --cr
>> On Wed, Apr 13, 2011 at 11:07 AM, Andrew O'Malley <aomalley at gmail.com>
>> wrote:
>>> Hi everyone,
>>> I have a pretty specific situation here that I'd love to hear your
>>> thoughts on:
>>> I have four panels of 5x6 Shiftbrite arrays, attached to plastic
>>> supports.  In front of each panel I'm placing an acylic sheet for
>>> diffusion, and on this sheet are several wires attached to an Arduino
>>> running the CapSense library.
>>> I can get useable data from the capsense arrangement running by
>>> itself, but when placed (3") in front of the shiftbrite arrary, the
>>> capsense values become extremely unstable (huge fluctuations making
>>> the data unuseable) when the Shiftbrites are receiving data.  The
>>> capsense circuit and the shiftbrite circuit are electrically isolated,
>>> as the capsense circuit is running from its own battery while the
>>> shiftbrite circuit is plugged in via a power supply; so I don't think
>>> it's noise from the power supply.  Is it possible that the array of
>>> Shiftbrites are giving off significant EMI while shifting data?
>>> If this is the case, anyone have any suggestions for add-on shielding
>>> for the shiftbrite array/cables?
>>> Thanks for your time and attention!
>>> Andrew
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