Ok, so let's consider just the PWM and ADCs. The two chips I am using are £3.40 total for one off. A Mega644 would cost maybe £4.70, so already it's looking more expensive. You might be able to find a cheaper micro to do the job. But you still have the disadvantage of having to develop the code and have to program updates.
If the micro had more interesting processing to do it would make more sense, but using firmware to do a low level processing job is an unnecessary complication. One thing a micro could do is to manage set temperatures, but that is such a trivial task it is hardly worth offloading. What would be useful to offload is driving the steppers, but that is the hardest function to divide up and maintain synchronisation.
So I am really struggling to see what the advantage of the extra micro is, when you go into the analysis.
Before I found the PWM chip I did a search for a suitable micro and came up with some candidates. If the PWM chip is unsuitable, then I would look at again at using a micro. I think it would be a fun little project to do, but I already have plenty of those on the go :) I am currently looking at building an LPC1769 based board which is compatible with RAMPS-FD, then you could use more easily use Smoothieware etc. Then there is also a board with a Cortex M4 with hardware FPU which would be pretty interesting for non-cartesian geometries. So ideas for boards are plentiful, what takes time is writing the firmware, so my goal was to make one board which doesn't require firmware.
I'll make the same offer as before, if anyone wants to commit to writing the firmware, I'll design and build a board with the processor of their choice.
If the micro had more interesting processing to do it would make more sense, but using firmware to do a low level processing job is an unnecessary complication. One thing a micro could do is to manage set temperatures, but that is such a trivial task it is hardly worth offloading. What would be useful to offload is driving the steppers, but that is the hardest function to divide up and maintain synchronisation.
So I am really struggling to see what the advantage of the extra micro is, when you go into the analysis.
Before I found the PWM chip I did a search for a suitable micro and came up with some candidates. If the PWM chip is unsuitable, then I would look at again at using a micro. I think it would be a fun little project to do, but I already have plenty of those on the go :) I am currently looking at building an LPC1769 based board which is compatible with RAMPS-FD, then you could use more easily use Smoothieware etc. Then there is also a board with a Cortex M4 with hardware FPU which would be pretty interesting for non-cartesian geometries. So ideas for boards are plentiful, what takes time is writing the firmware, so my goal was to make one board which doesn't require firmware.
I'll make the same offer as before, if anyone wants to commit to writing the firmware, I'll design and build a board with the processor of their choice.