i'm using optical limits as my home and limit switches for my mill. the switch when triggered sends a +5volt signal to the computer. however, pins 10, 11,12, 13 have 4.5 volts on them when the optical switches aren't connected. my optical switches are wired to send 5 volts to the computer to create a trigger event. i thought that pins 10-13 were input pins? what am i doing wrong?