[Lab] Arduino CapSense library + Shiftbrites + interference

Adam Hill theadbo+modlab at gmail.com
Wed Apr 13 12:11:22 EDT 2011

I think that since we're just trying to use the tinfoil to distribute the
charges it's charges evenly (to cancel the field it feels coming from the
cables), I don't think it's necessary to ground the tinfoil, but I guess it
won't hurt to do so.


On Wed, Apr 13, 2011 at 11:55 AM, Tom Burns <tom.i.burns at gmail.com> wrote:

> On this topic (I build synthesizers and for some reason keep using plastic
> cases so the it is relevant to my interests)
> Usually when wrapping something in tinfoil the next step is to attach the
> tinfoil directly to ground.  I'd be interested if you find a noticeable
> difference with the tinfoil attached to ground compared to tinfoil not
> attached to ground.
> Cheers,
> Tom
> On Wed, Apr 13, 2011 at 11:52 AM, Adam Hill <theadbo+modlab at gmail.com>wrote:
>> Hi Andrew,
>> I suspect that your EMI thesis is the correct one. I see that on the CapSense
>> arduino page <http://www.arduino.cc/playground/Main/CapSense>, it notes
>> that "At its most sensitive, the sensor will start to sense a hand or body
>> inches away from the sensor" so I'm sure the array's are sufficiently noisy
>> for the sensor to notice, especially when they're shifting! You could try
>> wrapping the cables in tinfoil but other than that I can't think of any good
>> solution except to put the setup into some kind of Faraday box<http://en.wikipedia.org/wiki/Faraday_cage>
>> .
>> BTW, care to share a few pics of the setup?
>> -a
>> 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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