Like I mentioned on the cnc page I used the circuit and layout by PMinMO to drive my stepper motors. At the time his design was "open source" but it is no longer.
I designed a breakout board to connect drivers for four axes plus a spindle control relay to one parallel port. The enables for all four drivers are tied together to pin 1 on the parallel port, and the spindle relay is driven by pin 14. Pins 2-9 are the step/dir outputs for the four axes as usual.
Attached below are the Eagle schematic and board file. The board layout is single-sided and the circuit is designed with robustness in mind, not cost savings. The breakout board has regulators to run the logic supplies on the PMinMO boards. Each board has its own regulator. The input for the logic supply can be any old transformer, even a 6.3V filament type.
The driver transistor for the spindle control relay is a low-side switch so you can use it to drive any convenient relay with pretty much any available voltage (I used the 40V that drives the steppers.) Like always, be sure to put a suppressor diode across the relay coil.
This circuit and layout are released under the terms of the GNU General Public License (GPL).
Files attached to this page: