DRV8825 compatible servo control with Digispark Arduino

This project is intended to provide a simple solution for using servos with CNC and plotter projects based on GRBL Arduino firmware (and CNC shield). Of course it is possible to use a modified GRBL firmware and drive the servo directly from the main Arduino. However, this requires specialized firmware and often specific Gcode instructions. This project strives to use a Digispark (Attiny85) to imitate the DRV8825 stepper drivers to control the servo. This way you can use generic Gcode and the Digispark takes care of converting the Z axis commands to servo movement. My goal was to make this as simple as possible so anyone can do it. It would also work on other axes, but placement of the module might become less trivial and my main focus was the Z axis (as for 2.5D plotter like movement).”