I do not know if the Digispeed is fully isolated, so be sure to confirm this befor using it on your machine.
The reason I say this is because some DC Motor controls, Like the ones from
www.Beel.ca are at mains voltage and the signals CANNOT be grounded to anything - especially the computer.
My first attempt at making a frequecy to voltage converter was not isolated - as such, when I connected it to the spindle drive board, I fried my computer. So, please take the time to make sure everything is isolated if it is needed with your motor drive.
Chris