home | list info | list archive | date index | thread index

reading Hollerith cards - was 5.25" floppy reading

On Mon, Jan 15, 2024 at 04:45:03PM -0500, David Patte wrote:
> So, i guess its passed the time to convert some my my 80 column
> Hollerith cards, then.

Those should be doable,  Just scan them in using a dark background so
that the holes are visible and use some image-processing software to
pull off the data.  Way easier than trying to read the magnetic bits on
the surface of a 5.25 floppy disk!

Anecdote: As teens, a friend and I got a camera and Porta-Pak through
the NFB "Challenge for Change" programme out of Montréal.  To splice
helical scan video tape without any glitches, you had to be able to "see"
the timing track on the magnetic tape, so we had some magic solution
(carbon tetrachoride?) that we could wipe on the tape that had super-fine
magnetic particles suspended in it and when dry would show the location
of the timing track pulses.  That let us cut the tape in the right place
and ensure that the timing tracks of the two pieces lined up properly.

Alas, because it's helical scan, the usual tape splices were a one-second
"wipe" that went from the scene on the first tape to the scene on the
second.  (It took about a second or so for the splice to migrate from
one side of the spinning tape heads to the other side.)

We wanted a "jump" cut that didn't have this wipe, so we would find the
splice point, tension the tape against the spinning heads so that the
heads would polish the tape along the helical track, and then we would
cut along that helical track to make our splice.  The diagonal splices
were maybe six inches long or more, but they worked!

-- 
| Ian! D. Allen, BA-Psych, MMath-CompSci  idallen [ at ] idallen [ dot ] ca Ottawa CANADA
| Home: www.idallen.com  Contact Improvisation Dance: www.contactimprov.ca
| Former college professor of Free/Libre GNU+Linux @ teaching.idallen.com
| Improve democracy www.fairvote.ca and defend digital freedom www.eff.org

To unsubscribe send a blank message to linux+unsubscribe [ at ] linux-ottawa [ dot ] org
To get help send a blank message to linux+help [ at ] linux-ottawa [ dot ] org
To visit the archives: https://lists.linux-ottawa.org

message navigation