[Mag-stripe readers]

I have had success reading and decoding some data from magstripes using a head from a tape player. I used a head from an old car tape deck, so it is stereo and also able to read from both halves of the tape (so there are 4 coils total - l/r side 1 and l/r side 2). I connected one of the coils to a stereo jack, plugged it into the PC's microphone input and used Audacity to record .wav files.

I saw some significant differences between different PC's - some work and others do not. Using a multimeter, I measured the voltage from the microphone jack and found that sometimes the left channel (mic input) is 0v and the right channel is 5v, on another PC the left channel is 0v and right is 3.3v, on another left is 2.5v and right is 2.5v, on another left is 3.3v and right is 3.3v. Success varied between the different machines.

Usually the data is noisy - it takes several card swipes to record valid data. The amplitude of the signal is very low, so there is a lot of problems with noise. Also, on one of my PCs the signal was slightly offset, which combined with the low amplitude made it impossible for Sephail's decoder software to work. (but it does work with recordings from another PC)

I wrote my own version of a magstripe .wav decoder, it only understands track 2 data (BCD), and is not the cleanest code (but its purpose is just a learning tool for me, so that's ok). RapidShare link: http://rapidshare.com/files/284934800/mag-20090201.zip.html

The above RapidShare link also includes a sample.wav file that I recorded. (it's from track 2 of a Staples merchandise card)

So far I have only tried using one magnetic head - I suppose there is a difference in gain, etc, between different heads. I also haven't tried any kind of amplification circuit between the magnetic head and the sound card - a proper amp circuit would probably take care of a lot of the problems between recording on different PCs. (the only downside is that it is more complex - it is pretty cool that with only the magnetic head and a wire to go to a sound card, it's possible to read a magnetic stripe - it doesn't get much simpler than that)

A couple of things that may help others: the faster you swipe a card, the higher the amplitude of the signal (stronger signal). I have to do quite a fast swipe to get legible data. On the other hand, swiping very fast means there will be fewer samples of each bit - I set Audacity to record at 96 KHz (instead of 48) to double the sampling rate.

The 'Card-O-Rama' article from Phrack 37 seems to be THE reference on magstripes - most of the pages I read about magstripe decoding have referred to that document. It explains everything needed to decode magstripe data.

Photos of my magstripe reader, on flickr - I taped the magnetic head to the side of a piece of wood (or edge of desk) and then use a book as a straight edge to slide the card. It's not so easy to get a perfect swipe, but it is simple to setup and allows any track or unusal stripe placement to be read. (a little duct tape and it becomes a proper Red Green magstripe reader ;))

(edited 2009-02-27 to update expired rapidshare link)

(edited 2009-04-27 to update expired rapidshare link)

(edited 2009-05-25 to update expired rapidshare link)

(edited 2009-09-25 to update expired rapidshare link)

can you please upload again the wav decoder?

Thanks