I've been playing with a 2560 layout so I could use it as a drop-in processor on projects into a 104 pin header.
This is what I have, all routed and with the caps, crystal, and resistor on the bottom, and ICSP and FTDI header for easy programming.
Thinking about pin labels - do you think having them around the outside like this is clear, or would moving a bunch inside the pins would be more clear?
I think the way you have it is best.
Would you want a jumper option on +5 on the the FTDI?
Yes, that can be added. Jumpers to allow 5V and DTR to be disconnected.
Am waffling on pin names tho - go with raw port names like I mostly have now, or go with the IDE names, such as D0,D1, Dxx and A0, A1, Axx?
I am curious, how will this board be used?
EDIT:
If you enlarge the PCB add 6-32 mounting holes in the corners then you would have room for both the controller names and the IDE name side by side.
My plan is to have a 104 pin socket on perfboard, or a PCB eventually, that this would plug into.
Looking at a project where this and several other processors would be connected together.
Going to wirewrap them to start until I find a connection/interface scheme I am satisfied with, and then perhaps go to a larger PCB for them all.
This provides kind of a DIP option for me, and if something blows I can pull it out and insert another.
No mounting holes - part will be treated like a DIP part, just plugged into a socket.
Or it could use wirewrap socket pins for legs instead.
CrossRoads:
This provides kind of a DIP option for me, and if something blows I can pull it out and insert another.
I would find that sort of thing more useful if there were just two rows of pins like a regular dip chip. I realize that would make it longer and would probably make the routing more complex.
...R
Well, that's the engineering tradeoff, isn't it?
Remember the Intel/Motorola processors of the past, 1.5" to 2" square parts with 2 and 3 rows of parallel pins underneath? That's what I am after here.
Someone's already done a 2 x 50 DIP version of the Mega, I think using the leadless package. I wanted something more compact, yet still relatively easy to solder.
At 47.8 x 45.3, this still fits into the inexpensive 50mm x 50mm PCB also, vs jumping up into the 50 x 130mm range.
Great idea, would allow for easy replacement of processor.
Am waffling on pin names tho - go with raw port names like I mostly have now, or go with the IDE names, such as D0,D1, Dxx and A0, A1, Axx?
Go with raw port names, people that will use the " plug in mega " will know the translation
That's what I was thinking too. And then making adjustments in pins_arduino.h can be more flexible too.
This is one of the DIP style 2560 layouts that is available (but backordered apparently)
https://jkdevices.com/arduino-megamini
I think your design is better than that! And you don't things that you don't need, like the USB.
I've ordered a set of PCBs, we'll see how they turn out in a few weeks.
This is kind of interesting might be able to get some ideas here.
http://www.elecrow.com/tqfp64-breakout-board-08mm-p-355.html
$1.00 
Perhaps.
www.schmartboard.com and www.proto-advantage.com offer lines of similar components.
schmartboard are set up to be easy to solder. proto-advantage has board-stencil-solder kits, and will also order parts from digikey and do assembly for you.
