for communication b/w PC and controller which periperial you will be using… is it RS232 or USB… if you using RS232 use max232 in b/w that will take care for voltlage and the current part and if you using USB the in/p must be 3.6v and the current must not exceed then 500mA… the o/p from PC is defined by the device itself when it get enumarated… if you using Parallel one you and use a buffer like ULN or 74hct541….