In this project, the software does all the heavy lifting. The "dab" utility included in this article takes the raw DSP data from your sound card, decodes the FSK (frequency shift keying - a.k.a. Atkin Biphase) modulation from the magnetic stripe, and outputs the binary data. Additionally, you can decode the binary data using the "dmsb" utility to output the ASCII characters and perform an LRC check to verify the integrity of the data, provided that the stripe conforms to the specifications described in ISO 7811, 7813, and optionally ISO 4909 (for the uncommon Track 3). Becoming familiar with these specifications will help you understand the contents of the magnetic stripe when viewing the decoded data.
The provided software is more proof-of-concept than production code, and should be treated as such. That said, it does its job well. It is open source and released under the MIT license. Feel free to contribute. Requirements
- Linux (or the desire to port to another operating system)
- A configured 16-bit sound card
- Access to the /dev/dsp device
- libsndfile
Note that "dab" can also take input from any audio file supported by libsndfile. However, it must be a clean sample that starts at the beginning of the file. This is useful to eliminate the requirement of a sound card and allow samples to be recorded from another device (e.g., an MP3 player/recorder) and decoded at another time.