[Simh] Card Readers on PDP-11's

[Timothe Litt]

Yes, and until ~ the 1442, the IBM readers used a row of metal brushes
to read the cards (they'd go through the holes and contact a metal plate
on the bottom).  All the early IBM gear was mechanically interesting - I
suppose from their origins.  Springs, brushes, cams, levers, solenoids,
microswitches, belts and motors!  A mechanical engineering degree was
probably more helpful than an EE (or later CS)...

The 1442 (ish) introduced optical (incandescent lamp + photocell)
readers; Documation also was optical.  IIRC, it also had a taller path,
so was more tolerant of warpage/curled edges.  Toward the end, the light
source became LEDs. 

Anything that avoided contact with the cards helped reliability.  The
challenge for the designers was to have tolerances large enough to avoid
jams, but small enough to prevent picking more than one card, or
allowing skew in transit.

The off-line card sorters and reproducing punches (with the wired
plugboards, often used with mark-sense) were also mechanical marvels -
or monsters - depending on which side of the Field Engineers' toolbox
you stood.

On 13-Feb-20 13:00, Paul Koning wrote:
>
>> On Feb 13, 2020, at 12:17 PM, Robert Thomas <rft at asthomas.com> wrote:
>>
>> ...
>> The Documation card reader was fairly reliable and didn't chew up as many cards as the IBM reader.
> I can believe that.  The IBM card readers and punches I've seen (on a 360/44) had a pick mechanism that moves a metal block with a small step in it, sized to match the nominal thickness of the card.  This was supposed to catch the far edge of the card and *push* it into the throat of the feed mechanism.  If there was anything slightly wrong, it would accordeon-fold the card instead.
>
> The Documation readers had vacuum operated pick mechanisms that acted on the leading edge of the card.
>
> 	paul
>
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