The controller is completed, controlling motors from a PC's parallel port. I'm using a text editor to create the control strings that are then printed via CUPS. Yep, <File - Print>.

The work in progress is that I'm cleaning up some aspects of the circuit, creating documentation and incorporating some improvements.

The first improvement is the oscillator, Andrej Levstek] published research on Amplitude Stabilization of Quadrature Oscillators. The output of the current QO is 2.5Vp-p at 15Hz from an LM324 operating from a single 5V supply. Looking at the outputs with the scope's X-Y mode, I see a circle.

I've posted a schematic, adapted for a stand-alone motor driver, in the files section.