Spindle control board

A relay board for switching a milling spindle on/off. Wired to RAMPS port D10 using [Grbl](http://sourceforge.net/projects/grblforramps14/) firmware. Host software, run on an Ubuntu laptop, [GrblHoming](https://github.com/zapmaker/GrblHoming) and [bCNC](https://github.com/vlachoudis/bCNC). The latter one supports autoleveling which is very handy when milling PCBs.
The stepperdrivers are powered from 24V. Two 12V relays are used in series configuration here.
The case has been designed with Free