26 Dec
2002
26 Dec
'02
4:16 p.m.
On Thu, 26 Dec 2002, Sellam Ismail wrote:
You can always trace back the data lines inside the reader, to see if they
run to mechanical contacts or some sort of semiconductors. Just be
careful that you don't generate a ground loop if the ground on the reader
and the Apple are at different voltage levels and somehow associated -
like something on the lo-v side of the power supply connected to earth
ground.
Pat
--
Purdue Universtiy ITAP/RCS
Information Technology at Purdue
Research Computing and Storage
http://www-rcd.cc.purdue.edu
On Thu, 26 Dec 2002, Tony Duell wrote:
You should be able to tell... check if it gives a close to +5V output for
a high signal (relative to the 'return line') with, say, a 470ohm
resistor to ground. you may also want to check that it gives a close to
0V output for a low signal If so, you don't need the pullup resistors.
The first confusion is to whether it's a 7404
output (as specified here)
or a 7416 output (as shown in the diagram). The main difference to you is
that the '16 is an open-collector device. If it's that, you need to wire
a pull-up resistor (1k or so) between the output signal line and a +5V
supply (take that from the Apple). If it's a '04, then you don't need
these resistors.
That is indeed one main element of my confusion. Why do simple errors
like this make it past the technical writers?
How do I know for sure which to use? Is there some way I can check with a
simple volt meter or something? The M200 has a
fair amount of electronics in it, and I can assure you
that the outputs come from logic ICs, not from mechanical contacts. You
don't need optoisolators.
This is the opposite of what John tells me. You're both highly competent.
To whom shall I defer?