[getting old punched cards read]

From: Ethan Dicks <erd_at_infinet.com>
Date: Mon Apr 20 22:15:04 1998

> 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).

True. If you write the program to keep careful time (and reject cards with
fewer than 80 chars), it _might_work. There is, of course, a brute-force
approach - 960 phototransistors. Additionally, one could build a 4 dpi
scanner (12 pixels and a stepper motor). With the steppper from a 5.25"
drive and either a mechanical amplifier (lever) to pull the 7" stroke or
either a) multiple 12-bit sensors or b) one 80-bit sensor w/3" stroke,
it wouldn't be that hard to make, not that I have the time to make a
contraption of that complexity.

> 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.

So gut a mouse and stick a wheel in the wood block...
 
> It's therefore almost impossible to make a hand-pulled card reader.

Not with the reading accuracy of a mechanized reader, no.
 
> If you can solve the timing problem, it's probably easier/quicker to
> program the microcontroller in assembly language. PIC assembler takes
> about a day to learn...

I'm not worried about learning PIC assembler, it's a lack of a PIC
programmer and a portability issue... any boob that would have a deck
of cards to read should be able to put together a Stamp-based reader.
I wouldn't expect a straight-PIC reader to be as trivial for a non-
hardware hacker to assemble. Easier than hacking a PIC board would
be to build a C-64 based card reader... there's plenty of I/O bits if
you bogart the keyboard lines.

-ethan
Received on Mon Apr 20 1998 - 22:15:04 BST