The Naked Scientists

The Naked Scientists Forum

Author Topic: Why did a piece of sticky tape on the magnetic strip bring my card back to life?  (Read 14008 times)

Offline gsmollin

  • Hero Member
  • *****
  • Posts: 749
    • View Profile
My wife has worn out the magnetic strip on her debit card. Now, I would have been perfectly happy if she had just stopped spending money, but noooo, she went to the bank for a new one. The guy at the bank put a piece of tape over the magnetic strip, and gave it back to her. Now it works again. Why would this be? I would have guessed that a larger space between the magnetic strip and the reading head would have made the induced signal weaker, and more difficult to read, not easier. What's your theory?
« Last Edit: 18/02/2007 13:14:00 by chris »


 

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • Posts: 20602
  • Thanked: 8 times
    • View Profile
....Im in Retail.....we just give it a wipe with a cloth and that seems to work too...though I must admit I don't have a proper answer for you, but in our case it seems to clean the greasy deposits and gunch that accumulates and breaks the contact with the strip reader..........yet I share your consolation as my wife has the same knack of using her debit card......my theory on how to solve this problem is................divorce the wife !!

'Men are the same as women...just inside out !'  
 

Offline gsmollin

  • Hero Member
  • *****
  • Posts: 749
    • View Profile
Neil, congratulations on your 1,000th post! I don't have a premium to give you, but you have my permission to scan something out at work for yourself.

Yes, cleaning the card makes sense. That one I understand. Here is my theory, since no one has posted one: I speculate that the reader has an automatic gain control (AGC). The AGC sets the gain of the pickup lower for a card with a strong magnetic signal, and higher for a card with a weaker magnetic signal. After enough abuse, the card gets a varying signal, with some very strong signals, and some weak ones. If the weak signals are caused by dirt, one can clean it. If the weak spots on the card are permanent, then the reader can't record them. If one puts tape on the magnetic strip, the entire signal gets weak, and the AGC increases its gain to read the signal. Now the weaker signals are still weaker than the stronger signals, but the dynamic range between the weaker and stronger signals has been reduced, because of the inverse-square-law v.s. distance of the magnetic signal. So the reader can now record all the signals again.
« Last Edit: 13/06/2004 23:52:45 by gsmollin »
 

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • Posts: 20602
  • Thanked: 8 times
    • View Profile
Thanks gsmollin, and I appreciate your giving me permission to award myself a pressy.:D

Your answer sounds great to me....hopefully there is somebody here who can confirm your theory...it sounds completely plausible though and I'd be surprised to find if you've not hit the nail on the head with that one........

all the best

Neil


'Men are the same as women...just inside out !'  
 

Offline tweener

  • Moderator
  • Neilep Level Member
  • *****
  • Posts: 1144
    • View Profile
Sounds like a good theory, but I really have no idea.

----
John - The Eternal Pessimist.
 

Offline OmnipotentOne

  • Sr. Member
  • ****
  • Posts: 146
    • View Profile
Well obviously the strip is magnetized, and over time maybe the code it carries gets weaker? So putting the tape over it might help to remagnetize the or amplify the weakened poles?  Maybe it just helps the scanner to read the card better, thats all I got.

OO

To see the world through a grain of sand.
 

paul.fr

  • Guest
Giving explinations in written, not oral form is not my thing but here goes.

If i remember correctly, the magnetic strips contains all the 1s and 0s. In tern they are read by the card reader.
Now over time and with regular use tiny particles of the magnetic strip are abraded and move accross the strip giving the card reader a false reading, ie a 1 where are 0 should be.

Putting a piece of tape accross the strip weakens the signal from the stray 1 or 0 and so the card reader will not now be able to read it.

or something like that.


Paul
 

Offline Soul Surfer

  • Neilep Level Member
  • ******
  • Posts: 3345
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
Was the tape clear?  if it was dark it might have had some "soft" magnetic particles in it that picked up the residual magnetic pattern on the caed and effectively amplified it.
 

The Naked Scientists Forum


 

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