On Thu, 26 Dec 2002, Tony Duell wrote:
> 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?
> IIRC, the 'return' pins are just grounds. They're all linked together
> inside the reader, and linked to the reader's 0V rail. The idea is to use
> twided pair cable, one wire for the signal, one for the return. On
> short-ish cable runs you shouldn't need to do this -- just wire up some
> of the 'return' wires to ground at the Apple end.
Ok, this is also what John Lawson instructed, which makes sense. My cable
is less than 10ft long (about 3m).
> 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?
(I would prefer to defer to you because it means far less work for me ;)
Sellam Ismail Vintage Computer Festival
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Received on Thu Dec 26 2002 - 16:04:00 GMT