[visionegg] Re: DAQ LPT IN
- From: Christophe Pallier <pallier@xxxxxxxxxxxxx>
- To: visionegg@xxxxxxxxxxxxx
- Date: Mon, 01 Mar 2004 18:34:32 +0100
Markus Bongard wrote:
Hello gentñle persons,
I just tried the demo from the DAQ folder to read in a trigger signal
from the lpt port. For some reason the given example does not "wait"
as exspected from the code - in contrast it directly starts the
animation. In other words: after starting the demo it seems that the
lpt port is already set to "trigger" the animation. Any suggestions?
Just an idea:
Is your triggering system "correctly" wired?
Did you check if the bits from in the parallel port registers are as you
expect?
I am saying this because I once had a similar problem with a too
simple-minded wiring
(see fig.1 of http://www.lscp.net/expe/doc/parallel/parallel.html).
Then, I learned that the parallel port pins can be in one of three
states: 0, 1 and high-impedance.
An external 4.7k resistor can be used to pull the pin high (+5V).
When in this state, your external device can pull the pin low and have
the control port change detect a change.
(see figure 2 in http://www.lscp.net/expe/doc/parallel/parallel.html).
Christophe Pallier
http://www.pallier.org
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