The family of [Chris Patty] decided that their holiday gifts would have to be handmade. So, he decided to make something new for his father: a jukebox with a twist. Instead of a touchscreen or web interface, his jukebox uses swipe cards. To play a track, you find the card for the song you want to hear, swipe it, and the jukebox plays the requested track. The whole thing is built into a wooden box that hides its digital nature, which is built using a Raspberry Pi and a credit card stripe reader.
[anfractuosus] has been reading magnetic stripe card… optically!
While hackers routinely read and write stripe cards, this is the first time we’ve reported on optically imaging and decoding data from the magnetic stripe. [anfratuosus] used a magnetic developer which is designed to allow visual inspection of the magnetic stripe. The developer uses micron sized iron particles in a suspension which are dropped onto the stripe. To the particles, the magnetic stripe looks like a series of magnets lined up. Long magnets represent 0s and short magnets 1s. With each bit the orientation of the magnet changes, something like the diagram to the right. The magnetic field is strongest where the poles meet. So the iron particles are attracted to these flux reversal points on the stripe creating a visible pattern . There’s an awesome video of the process in action below.
While magnetic developer was designed for debugging faulty recording systems [anfratuosus] went a step further scanning the “developed” card, and writing a tool to decode the images and extract the card data. [anfratuosus] doesn’t mention any particular application, we love this circuitous hack anyway!