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Sunday, October 24, 2004
The magic plastic bag I wouldn't have believed it if I hadn't seen it. The cashier told Cheri how much her purchase was... she pulled out her credit card and asked him for a plastic bag. I shot a puzzled look back and forth between her and the cashier. He gave her one, and she proceeded to insert her credit card into the bag and then swipe it... with the plastic bag on it. I was like, "Huh?" Apparently, cards that have magnetic strips that are "dead" and won't be read by the self-scanners can be inserted into a plastic bag and then they miraculously work. (Check out #18 on this page.) Being me, I had to know why this worked. What did we ever do before Google? Here's the deal. Standard bank cards use the F2F (Aiken biphase) modulation scheme, in which flux reversals encoded in the . . . eh, too much information. Let's just say that when you swipe the card through the reader, the magnetized particles in its stripe generate a signal with "ticks" in it at intervals that the machine is able to interpret as digital ones or zeros. A scratch or other defect in the magnetic stripe can cause a spike (i.e., brief fluctuation) in the signal that a too-sensitive reader will interpret as a tick, meaning that the encoded data will fail the parity check (the numbers won't add up right) and the card won't work. Wrapping the card in plastic increases the distance between the read head and the magnetic stripe, thus reducing the strength and crispness of the signal and smoothing out anomalous fluctuations. Behold, the card works.Don't say I never taught ya anything. UPDATE: From Paul, What also works: a piece of scotch tape across the magnetic strip. Voila! No more plastic bag waste... That's what I like to hear... magic AND environmentally friendly! | private feedback | |
Hey! I'm Shane... a proud gay progressive Democrat who has recently relocated to New York City from Ithaca, NY. As I am no longer in Ithaca, I haven't quite decided the fate of this blog. Drop me a line!
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