[getting old punched cards read]

From: Philip.Belben_at_powertech.co.uk <(Philip.Belben_at_powertech.co.uk)>
Date: Tue Apr 21 08:45:47 1998

Tony Duell wrote:

> Punched cards have one major design bug IMHO that's not shared by paper
> tape. There's no 'column reference' on a card. On a tape, you can strobe
> off the sprocket track, but alas on a card a totally unpunched column is
> valid (=a space character).
>
> My Documation M200 uses the leading edge of the card as a reference. It
> then counts pulses from a toothed wheel/pickup head on the card roller
> shaft to deteremine where the columns should be.
>
> It's therefore almost impossible to make a hand-pulled card reader.

I rather liked Allison's long array of photodetectors (of whatever
flavour) to tell you where the leading edge is.

But why not have the same wheel to determine the position, but the card
turns the wheel rather than vice versa? You lose the non-contact
element of hand pulling, but you don't get motors chewing delicate
cards.

Philip.
Received on Tue Apr 21 1998 - 08:45:47 BST