Yes you will need a resistor. Lets assume you want
to monitor a switch closure. And that the switch will
close to ground. Connect a resistor to 3.3 volts to
the GPIO of chioce. Then to the switch.
3.3 volts-100k ohm-GPIO-switch-GND
Whats happening is when the GPIO is programmed as an
input the voltage of the pin will be right smack in the middle
of the threshold of being a 1 or a 0. So anything touching
it will fool the input latch causing misfires.
Hope this clears things up
-------------- Original message ----------------------
From: "Joseph R Lust" <lifeoflust@...>
> Hello all,
> I am a biomedical engineering student working on a senior project centered
> around using a gumstix 400mx as the brains of a redesigned medical device.
> I've got a buildroot made in ubuntu and have been compiling programs for the
> gumstix for a few months now. My problem lies with the ability to pull, set,
> and interrupt the GPIOs. The gumstix site says next to nothing about this
> and I have only found bits and pieces on the email board.
> I have gotten both the GPIO setting code and the GPIO-event program of
> Dave's, but it seems that when I monitor the gpio-event for any of the
> gpio's on the Breakout GS board (say LCLK - LDD0) I get an endless stream of
> events when anything conductive has been touched to the solder pads (even a
> pencil tip) let less a 5V source. They are in the pattern of FFRRR
> repeatedly, only limited by the set debounce period.
> Is there a certain circuit that should be used here such as pull-up or down
> resistors? I am not much of an ECE, so I am unsure of this aspect. Also, I
> have noticed that on the oscilloscope there is a 60MHz carrier on all the
> GPIO pins mentioned above with reference to the gumstix power supply
> (presumably from the AC brick). The GPIO's will eventually be used to drive
> some FETs and poll a quadrature encoder. Thanks.
> Joseph R Lust
> University of Rochester
> Rochester, NY, 14620