I just ordered an Arduino Mega. When I saw the amount of public open source code, and hobby/robotics accessories available I had to try.

I found some MODBUS software, and the MACH3 can 'open' the board.
I am not a good programmer at all, but I want to try to get them talking. 
My plan is to try every combination of setting and jumpers on the board,and in MACH3  until I get some response.
If anyone has any better ideas or resources I am very interested

I've had a bit of a play with this http://sites.google.com/site/jpmzometa/arduino-mbrt - seems to do what it says on the tin.

Yes!  I have that program and I now have it working. The adruino is fantastic. So is the software. I am working on adding more modbus functions,. I have analog in working now, have constructed a wizard, will post it when done. One small puzzle?  I have to click OUTPUT in the brain editor mod bus setup dialog.
 to read the analog and post it to a DRO.

I also have a pokeys, and it's interesting to compare them. The PWM is much better on the Pokeys as it is 16 bit not 8 bit. I am also looking for encoder and mpg sub routines. For the adruino.  Having lots of fun for $60.

  I wonder if someday I can use the  adruino to take the  place of a smooth stepper ? Of course I cannot write the code, just wondering. 

One small puzzle?  I have to click OUTPUT in the brain editor mod bus setup dialog.
 to read the analog and post it to a DRO.

Can't help you there - never used brians  

I wonder if someday I can use the  adruino to take the  place of a smooth stepper ? Of course I cannot write the code, just wondering.  

Hmmmmm - doubt it. Remember the serial connection to the Arduino is actually just RS232 over USB (if that's the correct way of putting it) so I don't think you would get the speed apart from anything else - but I'm not sure.

Is it the serial connection or crystal that matters when it comes to clock speed? What speed does Mach3 require?

My thinking was that both need to be at least considered for a generalized solution. Consider the activity on the serial line as commanded moves get smaller.

Ian

I would like to use an Arduino Mega 2560 to control the stepper motors, homing switches and extruder/laser output via mach 3 without rewiring to a parallel port.  Understanding that it would take a different firmware load on the Arduino to change it from a gcode interpreter to a hardware controller (similar to the smoothstepper).

Has anyone done this?

Why?  I have two 3D printers and I am building a laser cutter with Arduino Mega 2560 controller.