Reading credit cards with a tape head

A company called Square is giving out free credit card readers that turn any iPhone or iPad into a Point of Sale terminal. [Steve] got a hold of one of these tiny peripherals and did what any sane person would do: tear it apart and learn how it works. This bit of hardware is a little unimpressive; unsurprising because Square is giving them away. With simplicity comes an ease in understanding, and [Steve] was able to successfully read his own credit card with this tiny and free credit card reader.

[Steve]‘s work in decoding credit card data builds off [Count Zero]‘s article from the bbs days. Basically, each credit card has two or three tracks. Track three is mostly unused, whereas track one contains the card holder name, account number, cvc code and other ancillary data. Track two only contains the credit card number and expiration date.

The only components in the Square card reader are a head from a tape player and a 1/8″ microphone jack. The magnetic head in the Square card reader is positioned to only read track two. With a small shim, it’s possible to re-align the head to get the data from track one. After recording an audio file of him sliding his card though the Square reader, [Steve] looked at the number of times the waveform flipped from positive to negative. From this, he was able to get the 1s and 0s on the card and converted them to alphanumeric using the 6-bit ANSI/ISO alpha format.

[Steve] isn’t going to share the code he wrote for Android just yet, but it should be relatively easy to replicate his work with the Android tutorial he used. Also, yes, we did just pose the question of how these Square credit card readers work just hours ago. Good job being on the ball, [Steve]. Tips ‘o the hat go out to [Bobby], [Leif], [Derek] and anyone else we might have missed.

EDIT: [Stephen] sent in his teardown minutes after this post went live. Hackaday readers are too fast at this stuff.

Hackaday Links: April 18, 2012

Sandcasting at the beach

[mkb] sent in a video he found of [Max Lamb] sandcasting a stool at a beach in England. The material is pewter, or >90% tin with a little bit copper and antimony thrown in for good measure. While we’re sure there will be a few complaints from environmentalists, it’s still a cool video to see.

Your project needs an OLED display

Here’s a Kickstarter for a tiny 96×16 OLED display. Connect this thing to any I2C bus and you get a 15×2 character display (or a graphic display if that’s your inclination) very easily. Thanks to [Chris] for sending this one in.

Here’s one for a larf

[Ryan Inman] is suing 20 companies because he got mercury poisoning from vacuum tubes. Read that last line again. Most of the companies that sell antique/repro/hard-to-find components like Angela Instruments, Antique Electronic Supply, and even eBay are listed as defendants in the case. This might put at least one company out of business even though they never sold [Ryan] a vacuum tube edit: they did sell him a neon bulb, and courts are generally idiotic when it comes to technological issues. It’s hilarious and sad, so we’ll keep you updated if we get more info.

Nostalgia, the pain from an old wound

The Adafruit blog posted an excellent piece on the Apple ][ game Rocky’s Boots, an educational game from 1982 that teaches kids how to connect logic gates. You can play this game in your browser, but we’d like to hear our stories of ancient video games that teach you engineering concepts like The Incredible Machine or Widget Workshop. Leave a note in the comments if we’re leaving any out.

A question posed to the community

A company is giving away credit card readers that plug into the headphone jack of an iDevice. [J Smith] writes in to ask us if anyone has gotten one of these and opened them up. Like [J Smith] we’re expecting something a repeat of the CueCat where free hardware is opened up to everybody. If you’ve done a teardown of one of these card readers, send it in.

3DS homebrew

[Mike] sent us a link to [neimod]‘s Flickr photostream. It looks like we’re on the cusp of tearing open the Nintendo 3DS for homebrew apps. Someone who uses this much hot glue must know what they’re doing, right?

Generating music with credit cards

mozarts_credit_card

[Steve] was browsing around at a local electronics surplus store when he spotted an old Tranz 330 point-of-sale terminal that seemed pretty interesting. He took it home and after disassembling it, found that it contained a Z-80 based computer. Because the 330 shares the same processor as other hobbyist-friendly devices such as the TRS-80, he figured it would be quite fun to hack.

While the Z-80 processor is pretty common, [Steve] still had to figure out how it was interfaced in this particular device. After spending some time reverse engineering the terminal, he had free reign to run any program he desired. After thinking for a bit, he decided it would be cool to use the terminal to generate music based on whatever card was swiped through the reader – he calls his creation “Mozart’s Credit Card”.

He found that just playing sounds based on the raw contents of the mag strips didn’t produce anything coherent, so he wrote a small application for the terminal based on the Melisma Stochastic Melody Generator. Music is generated somewhat randomly using various card characteristics, as you can see in the video below.

We think it’s pretty cool, but [Steve] says he’s always open to suggestions, so let us know what you think in the comments.

[Read more...]

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