15 Mar
2013
15 Mar
'13
1 p.m.
Hi all,
I need another project like I need a hole in the head. However, I am
definitely on the prowl for a way to store and retrieve information in a
more physical fashion. Something like a tape punch/reader, or a mark-sense
card reader. (I'd have to find or print some mark-sense cards...)
Back in the day I used punch cards, mark-sense cards, and paper tape.
There's a certain "coolness" to actually seeing and holding the data in a
physical format. I think it would be great for my kids to see, and/or help
me build a physical storage device, to give them a more visceral sense of
computing. You can't exactly see the bits in a flash memory chip.
All that said - I've looked for homebrew projects of this type, and haven't
come up with any great candidates. I'm not the most skilled person at
mechanical stuff, so I do seek a starting point for ideas or plans. Anyone
have any comments/suggestions?
Goal would be a method to store (could be as simple as #2 pencil), a method
to read, and a serial RS232 interface (that part I can build).
It's probably easiest to make an opticla punched tape reader. Optical
sensing is a lot easier than any form of mechanical sensing, and if you
can't get phototranssitors small enoguh to put on 0.1" spacing for the
read head, you could always use optical fibr to route the ligth from the
read head to the phototransistors. There's some historical precident for
that -- IIRc the well-know Elliot optical take reader used glass rods to
route hte ligth from teh ead head hols to OCP71s.
The advantaeg of tape over cards is that you can sue the sprcket track
to genrate a strobe pusle. With cards, you would noramlly note when the
elading edge of the card went past a sensor and then read the columns
after the card had moved a given distance. This requries a much more
precise drive mechanism, and one that won't slip.
As for dring the tape, either pull it through by ahd or use a
capstan/pinch roller to feed it. For the latter, the pinch rolelr from a
VCR would eb a reasoanble startign point, you could make the capstan in a
good home workshol (I have no idea what facilites you have). It only gets
hard if you want ot be able to stop the tape on a cchracter.
The punch is goign to be a lot harder. Even a hand punch -- one
ofthoseblocks with holes and a pin you push through to make a nole is not
essy to make. You need ot drill the holes accurately (position and
diameter) and you need to make an punch pin. Again _possible_, but not
trivial.
Does it have to be a well-known format? I am wonderign if you could make
a mark-sensing card reader that required a timing park on each column of
the card. Tht would get round the accurate drive mechanism problem, you
could sense the marks optically. And of course the (manual) writing
device is a pencilIf you _insist_ on making that yourself, I am quite
shure you could make charcoal, and that would make suitable marks on the
card.
-tony