The next step is to start on the Solder head interface board. It uses signal relays for the outputs and opto-isolators for the inputs.All of the signals enter/exit through a 50-pin Centronics connector.

Once thing I did release when starting to look at the H-02 board , is that I need nine relay outputs, and 11 opto inputs for the expansion port. Then there is a 4 bit single digit program selector switch, cycle start button on the front panel.

I like to use the selector switch on the machine to select and load the GCode program. Not sure how easy it is to do this, but it should be possible.

Looking at the I/O requirements, a single 2nd port is not going to be enough to deal with all these signals.

The solution I'm now leaning towards is to use the Ethernet Version of the Smooth Stepper. It has the equivalent of three parallel ports.