SparkFun Forums

[moryde]

Hello!

I am currently working on a project where I would like to read a punchcard that would look somewhat like the picture.

I will need 17 bits and I would like a width of aprox a playing card. (This a variable).

But do any of you got any ideas on reader such a card? As I see it there are two possible solutions (most found of the second one).

[*] there is the optical version, but I am quite frightened of the idea of aligning so many optical diodes, is this a concern?

[*]Then there is the mechanical version witch talks more to my design intention? How would you do a mechanical version? I am thinking of using the clamps of a battery holder and the simply disconnect them physically with the card? Do you think this sounds plausible?

What would you do?

thanks in advance

[esklar81]

I am currently working on a project where I would like to read a punchcard that would look somewhat like the picture.

To me, a "punchcard" has holes surrounded by paper, not indentations in its borders. Are all of your bits recorded as notches?

I will need 17 bits and I would like a width of aprox a playing card. (This a variable).

Based on your description and picture, it appears each "bit" is ~3 mm wide and extends ~10 mm from the edge of the card.

But do any of you got any ideas on reader such a card? As I see it there are two possible solutions (most found of the second one).
[*] there is the optical version, but I am quite frightened of the idea of aligning so many optical diodes, is this a concern?

I don't think you'll need to align 17 pairs. How consistent are the color and reflectivity of the cards? If they're consistent, you could use reflective sensors, such as these. If you put a row of eight of these above a row of nine of these, with the rows offset by half the spacing, it appears you could get 17 bits in the pattern you've described. (It appears that these may be small enough to fit in a single row, but they're surface mount devices (SMDs) and I don't know if you're comfortable working with SMD.)

[*]Then there is the mechanical version witch talks more to my design intention? How would you do a mechanical version? I am thinking of using the clamps of a battery holder and the simply disconnect them physically with the card? Do you think this sounds plausible?

It's not obvious what you mean by "clamps of a battery holder", but I'd be concerned about getting a spring contact that is firm enough to close reliably when paper is not there, but loose enough to open when paper is being inserted, rather than just bending the paper. (If your cards are something substantially more rigid and more moisture-resistant than paper, this may not be a problem. What material cards do you expect and how much risk of contamination, mechanical damage, or humidity (including from being in shirt pockets, for example) is there?)

Also, how are the cards to be moved in and out of the reader? My initial guess from your description is that the cards are inserted and removed, one at a time, by hand. If that's not correct, what is the intended mechanism?

What would you do?

If my guesses about what you're trying to do are correct, I'd probably build an array of five of the first sensors I mentioned and see if I can read the first five bits reliably. If that works, I'd expand to 17 bits. If my guesses are wrong, correct them and I'll give this some more thought.

While the thought is passing through my brain: How do you intend to read and process the data?

thanks in advance

You're welcome!

Have Fun,
Eric

[anhingus]

you might be interested in looking up herman hollerith on the web, the grand-daddy of electric card reading, and see how he did it.

[KeithB]

I believe Mr H (Beloved of FORTRAN programmers every where) used little pools of mercury, so his techniques might not be OSHA approved...

Pogo pins might work for a mechanical solution. You could even use two per bit as a redundant backup.

[propjohn]

What would you do?

I'd use a prealigned photo-interrupter [like this] and make the punch pattern [self-clocking]. To operate you'd swipe the punch pattern between the arms of the interrupter. If you have no control over the punch pattern you can have the card drive a wheel connected to an optical encoder. Or use a stepper motor to draw the card across the reader at a constant speed.

[coyote20000]

If it's just the edge where the data is I'd go optical.
Something like...
http://www.google.com/imgres?imgurl=htt ... x=81&ty=76

I think they are pretty cheap and I'd assume they could be mounted next to each other without interference.
(Of course I'd test two or three before going all out)

Dave

EDIT: Sorry, I see propjohn basically said the same thing..

[tecoist]

I personally have seen pogo-pin, optical, and long-spring-finger electromechanical readers. All of these approaches can work.