Tim has a how to on making a portable magstripe reader – “You will need a magnetic head which are very common I recommend a magnetic head from an old tape deck. It is important to be careful not to damage the head when removing it. The magnetic heads are usually secured with two screws. (Note: Do not discard the screws we will need them latter for mounting the head) You will also need a 3.5 mm mono phone plug (with a 2-conductor wire) you can easily find one of these on an old monaural earphone or in an electronics store. You will also need a soldering iron and some solder.” – Link.
Related: Magnetic Stripe Reader. Have you ever wondered what information is stored on the magnetic-striped cards in your wallet? Now you can find out. This project shows you how to make a magstripe reader for less than $40. MAKE 01 – Page 106.