Here is a nice solution to solve your problems connecting PS/2 devices (ex external capacitive touch pad, magnetic card reader). This connector is also very useful for connecting a keyboard + mouse using only one USB port. This cable is equipped with the conversion electronics - a small micro-controller that turns the PS/2 into "USB mouse" and "USB keyboard".
Tested with Raspberry-Pi, BeagleBone and Linux. Also tested on Windows and MAC where everything works without problems.