Thanks for the great response.
Dave Hylands wrote:
> HI Nicholas,
>> I'm new to gumstix, so I apologise in advance for the lameness of this
> No lame questions - just lame answers :)
>> What is a GPIO line and where can I learn more about it?
> GPIO stands for General Purpose Input/Output. It's basically a digital
> I/O line, that can be at logic low or logic high, if configured as an
> output, or detect logic low or logic high when configured as an input.
> So the logic low/high is the programmer's perspective of the world.
> 0 = logic low.
> 1 = logic high.
>> Can a GPIO line be used to attach a simple sensor (such as a motion
>> sensor with a power, ground and signal connection)?
>> The gumstix wiki provides an example of accessing the PXA's GPIO lines
>> from userspace. Can these be used to attach a peripheral?
> The hardware manifests these as voltages. For the audiostix, all of
> the voltages are 3.3v, so you can only connect sensors which are
> compatable with 3.3v.
> Sensors which work with other voltages require some type of voltage
> level conversions.
Ok, so let's say I've built a little circuit that output 3.3 volts
suitable for a GPIO line. Is there a physical pin on a basix/audiostix
2 to access one of the PXA's GPIO lines? In other words, how do I
connect my circuit output to a PXA GPIO? I can't see any on the basix,
but maybe the audiostix makes one available via the hirose connector?
Alternatively, the UCB1400 on the audiostix has some GPIO lines, but I
haven't yet discovered if the linux kernel has support for accessing
these. (cf. the PXA GPIO lines which /are/ accessible from userspace.)
Finally, if I were to build a circuit to interface to a sensor at a
different voltage, is there a pin on the basix/audiostix 2 which is
"logic 1". My circuit would switch between this logic 1 or logic 0
(ground) based on the sensor output, hence I would need a "reference
voltage" to know just what is logic 1.
FWIW, I have a vague idea of using a transistor as an electronic switch
between logic 1 and logic 0 in my sensor circuit. The transistor will
be switched by the sensor output, of course.
Maybe I need to go back to school...