The Naked Scientists

The Naked Scientists Forum

Author Topic: Magnetic Fingerprinting - Reading a Credit Card - Kitchen Science  (Read 10142 times)

Offline thedoc

  • Forum Admin
  • Administrator
  • Sr. Member
  • *****
  • Posts: 511
  • Thanked: 12 times
    • View Profile
Magnetic Fingerprinting - see the data which is stored on the magnetic strip of your credit card.

Read more about this kitchen science experiment.

Listen to the Experiment or [download as MP3]
« Last Edit: 20/03/2013 18:11:34 by _system »


 

Offline daveshorts

  • Neilep Level Member
  • ******
  • Posts: 2583
  • Physics, Experiments
    • View Profile
    • http://www.chaosscience.org.uk
We were sent some lovely closeup photos form Randy Hirsch


 

Offline wolfekeeper

  • Neilep Level Member
  • ******
  • Posts: 1092
  • Thanked: 11 times
    • View Profile
I was trying to work out if I could actually find a way to read off the magnetic poles. The problem with iron is that it sticks either way around (it's a soft magnetic material).

I figure if I could crunch up a ferrite magnet, put the crunched up bits on another magnet to orient them, and then paint one side, and then break it up again, it might be possible to read the poles by visual means.

I haven't tried it yet though. It might be fiddly to get the exact recipe right.
 

Offline SeanB

  • Neilep Level Member
  • ******
  • Posts: 1118
  • Thanked: 3 times
    • View Profile
The actual polarity is not relevant, as it is the changes that are read out by the read head and electronics. The actual polarity of individual magnetic domains is not important, the change is.
 

Offline wolfekeeper

  • Neilep Level Member
  • ******
  • Posts: 1092
  • Thanked: 11 times
    • View Profile
Depends what you want to use it for. I'm messing about with Halbach arrays and it would actually be useful to know polarities.
 

Offline SeanB

  • Neilep Level Member
  • ******
  • Posts: 1118
  • Thanked: 3 times
    • View Profile
Most card readers use a tape head, which is a basic coil with a gapped core, and follow it with a large amount of amplification that is AC coupled for stability. Thus the output is a differentiated representation of the magnetic recording, and pretty much all polarity information is stripped out when it is converted to a digital pulse train by a fixed point comparator. You get ( on the lowest data rate tracks) a clock and data that is robust and easy to recover, but which is not very high density recording.

Magnetic card media specifications allows a card to be paper with a screen printed stripe, something that is cheap and robust, but able to hold enough information to allow it to be used as a disposable parking token, or a more robust plastic laminated card that permanent parkers can use interchangeably on the machines.
 

The Naked Scientists Forum


 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums