[Arm-netbook] Testing: GPIO

[Christopher Havel]

I /designed/ that circuitry in the micro-desktop. I still have the paper
copy somewhere...

You can also do it with a dedicated DAC chip, which is the
easy-but-expensive way I hinted at.

But we aren't testing /that/ part -- the micro-desktop -- are we? If we're
testing the /card/, the card does not output anything remotely like VGA,
and, therefore, some kind of conversion is necessary in order to attach it
to a VGA cable as was being proposed in the email I replied to about that.

All you really need for this is a laptop PCMCIA or CardBus card cage, an
IDE cable or two, a couple 4051s and toggle switches on a slice of
perfboard, a 9v battery with connector and switch, and a cheap USB logic
analyzer attached to a laptop. You use the 4051s, switched manually, and
powered by the 9v battery, to act as input expanders for the logic
analyzer. Each 4015 turns one channel into eight and requires three "on-on"
switches -- with one "on" wired to +9v, one to ground, and the common to
the chip. You use the IDE cable for the wires ;) If you hook it up so that
you have one 4051 mux per logic analyzer channel, that'll give you 128 (!)
channels to switch with -- most USB logic analyzers, even the super cheap
ones, are 16-channel...

Heck, if you wanted to make the circuit "complicated" -- I could draw up
something that automatically iterated through the channels for you at the
press of a single button, switching at variable speed with a pot, a 555, a
resistor and cap, and a couple 4017s and 4051s. You'd only need /one/
channel for that -- so you could even use an o-scope there. Heck, I could
do it with that circuit and my old, old Tektronix 422...

I'm honestly surprised that this sort of idea hasn't been mentioned yet.