Well, it was unavoidable, I'm going to need a fab D board. Yup, my design of the optoisolation on the board was quite wrong and I've decided to completely change it. To prove the new design, I decided to fab up a quick opto isolation board to test out all of the inputs and outputs of the parallel port. I used pluggable resistors to dial in the values and get the transistor biasing where I wanted it.
Here we see the low speed optos that will handle the home, limit, estop, spindle, and coolant IO. The yellow push-button switches are for testing the home, limit, and estop inputs.
You just have to love toner transfer for quick protos. I had this board etched and built in about an hour.