I spent a little time last night looking over the wiring and found that I had reversed 2  wires on each stepper motor........which is why my motors were traveling in the "opposite" direction that I expected. Gotta say, I felt pretty dumb but pretty happy to catch that one.

Tonight I loaded up a gcode file I had created a while back of the sparkfun logo (they have a pretty comprehensive logo page in their about section with a ton of different logos, shapes, etc, etc, in high quality vector (PDF & EPS) files. I used cambam to generate the code (flawless I must say) and have just been waiting to use it.

Turns out that my mill actually works. I shouldn't bee too surprised, I mean after 3 years of tinkering around you'd figure I'd get lucky sooner or later. My next task is to design a dremel mount. At my rate that will probalby take a year, but at least I can draw with a pen until then :-)

In my last post I mentioned having a problem over flowing the tiny arduino serial buffer while streaming gcode from one unit to another. Since then, I have talked to a few people about the matter, and one suggested implementing some sort of hardware flow-control .

"What it seems to me like you might need is some physical hardware flow control, just a wire running between the master and slave independent of the serial line. So maybe the slave would send some data, and wait for a change on the line, whereas the master would wait to receive data, process it, change the line status, rinse, repeat."

How the implementation ended up going down was something like this:

1.) Connect wire between arduinos (Slave: Pin7 to Master: Pin13)
2.) Master: after each byte recieved, check the status of the buffer. By issuing the serialAvailable() command returns the number of bytes available to be read from the buffer. We know the buffer is only 128bytes in size, so we can do a simple if statement:
   if(serialAvailable()>= 128) {LEDPORT |= _BV(LEDBIT);}   //turn on LED13

3.) Slave: before sending byte, check the status of pin7
           while ((c = file.read()) > 0)
          {
             while(val = digitalRead(flowpin) == HIGH)
            {
               delay(100);
            }
            Serial.print((char)c);
          }
Here is a video of the setup in action. Keep in mind that the SD "shield" is not a shield, i.e. the pins are not repeated on the top of the shield. So, in order to get this to work, i had to use the mini-bread-boards and because of that, this looks a lot more complicated than what it is.

Also, on a somewhat related note: grbl made it on MAKE!

It's completely possible to run an Arduino based headless CNC machine! Here is the current setup I am using:

Hardware:
1.) SD Shield from SeeedStudio - as a side note: I hesitate to call this a "Shield" as it doesn't repeat the female headers on the top, so by using this you essentially lose access to your Arduino's V and GND ports. You need access to the GND port so you can tie the two GNDs from each Arduino together. I have circumvented this limitation by using two mini bread boards, as shown here: Also, it would be an easy enough fix to replace the current male headers with something like these, but I just have not gotten around to doing that.

It's not the most elegant solution, but it's working.... (as a side note: the USB cable in "master" is just to power the device, not communicate with it. I have since switched to a wall wart!)

Software:
Master Arduino: In my setup, I am calling the "master arduino" the one that parses the gcode. For this I am using a program called grbl. IMO, this is the holy grail of arduino based gcode parsing. you can download it here, or read a little about it here. I actually found it via the contraptor project, here. You can see grbl in action here!

Slave Arduino: The arduino that is connected to and reads the SD card. After pouring over a bunch of different fat libraries for arduino I settled on Bill.Greiman's fat16lib. It was very easy to implement and did exactly what I needed it to do.

I have had some problems overflowing the Master's buffer, but this is mainly due to the fact that I'm having a hard time setting up flow control. What I need to have happen is for the slave Arduino to Serial.print a line and then WAIT until it receives the "OK" from the master. I can't figure out how to do that reliably, so occasionally i overflow the master's buffer.....

Here is the physical board and wiring. It is "flipped" 180° compared to the "schematic" above.