Greg,

In response to your message:



I have been looking at relays that control the spindle and agree with you that you do not want to switch that on the controller board. I had planned to use a small relay rated at about 2 amps 30V that could be used to switch a full size 120 Volt 16 AMP type relay off board. What are your thoughts regarding this? You mention a solid state solution. Would this be on board or off board?
Off Board, most SSR's can be driven with 20ma or so:

Example : http://www.futurlec.com/Relays/SSR10A.shtml

One discrete open collector driver output from the board.


The limit switches go back to the PC, but the panic switch and the limit switches are also hardwired to the drive enable on the controller chip and would shut down the motor drivers with out software intervention. This is to prevent a motor run away. This is often a UL saftey requirement on boards of this nature.

Also a simple three terminal regulator could be added to the board, it would also require some DC decoupling capacitors (filtering) and these can be big and eat up a lot of board space, but the parts would not have to be stuffed if one did not want to use them. I think PCB boards cost about $2 per square inch or so including fabrication, and so this might be a $4 PCB cost adder, what do you think?
www.olimex.com DS approx $1/sqinch prototype.
My 3977 proto board from them:

http://webpages.charter.net/pminmo/board2.jpg
To me it's worth it for several reasons. Grounding, wiring noise, simplicity and elegance.




Thanks for the input,

Greg

Take care,

Greg