3-Axis GRBL CNC stepper controller with Arduino Mega328

This is my take on a GRBL Mega328 3-axis stepper driver board for my CNC mill. It is designed for the new Trinamic TMC2100 stepper driver chips on a breakout board sold by Watterott-Electronics (which I really like, because they are really cool (they decrease the current when the motor is idle, and they are silent =;) available here link ).

But you could also use other stepper-drivers like the Texas Instrument DRV8825 or Pololu A4983 if you like.

• There is only one power-supply input (24-45 Volts) and the board uses a step down converter to generate the 5V/3.3V supply for the controller.
• All inputs are galvanically isolated with opto-couplers and a DCDC converter for supplying the secondary side [link]( http://www.reichelt.de/index.html?ACTION=3;ARTICLE=35024;SEARCH=SIM1-0505%20SIL4) , so no problems with EMV going into endstop cables and doing funny things to the CNC controller.
• Atmel Mega328 contoller with FTDI USB chip on board
• uses the really fantastic GRBL firmware for arduino

On the software side I use bCNC as g-code sender and autoleveling platform for milling PCBs.

The board and schematics where designed with KiCAD

To be on the save side I have added a cooler for the stepper drivers. It uses a printed duct and a 40mm 5V fan.

Aug-29-2015 uploaded newest sketchup file, with a easier to print fan-duct and a improved bottom and top enclosure parts.

I have a few professional made PCB's now (just the bare PCBs, no soldered parts), so if somebody is interested in those, let me know.

Update!
There was a stupid mistake in the FTDI (USB) section, VCC was connected to 3.3V and that caused the USB connection to fail at random times or completly to fail.

I fixed the PCB and schematics.