Do you happen to have a shield board drawn up?
I was thinking of this as a base board which would get shields attached to it since the USB is needed to program the chips.
Were you talking about a sketch of the board, or a sketch of one that could accept shields?
I can't think of a good way for this board to be a shield because then how to program the CPUs but I'm open to suggestions! 
Actually I was wondering if you have just a basic proto shield drawn up.
How do you switch the USB between the 4 processors?
@ericski
I have the gerbers and DipTrace PCB files for the proto board I show in the earlier post, or I can take a better photo of that one which shows the layout in more detail.
The USB is switched by a DP4T switch (seen in the picture) this swaps the TX/RX from the USB to the RX/TX of each processor. The power, ground, and reset from the USB are wired to each processor. This means when you're uploading a sketch, all the CPUs reset and the one selected by the switch starts receiving the sketch, while the others start running whatever program is loaded.
Hope that answers your question.
That answers my questions, thanks.
Hi Folks -
I've been revisiting the layout and it occurred to me that switching to an SMT version of the CPU may not actually be too bright since it does not allow swapping or upgrading the component to different versions (i.e. 168 to 328).
Would anyone care if the board is slightly bigger but you had DIP sockets instead of a soldered on CPU? Here are some benefits I can see for the DIP version:
- Allows upgrading to other CPU cores (ATMega 8, 168, 328, or others)
- Should you fry or otherwise mess up one CPU, you could swap it out for a replacement
- Board could be sold without CPUs as a lower cost option and user could acquire or scrounge CPUs to populate it with.
Let me know what you guys think. I will still switch out the caps/resistors for SMT which will save some space.
Here's a rough guestimate at the layout:
I think DIP socket mounted AVR chips is the best way to go for a development system. As they say, s**t happens and it would be nice to limit damage costs to the minimum.
Lefty
I think I have an idea about 4 cores + using shields.
This picture shows the idea for how each one would be laid out on a board. Each board would not have the individual power & USB. I figure the power & USB could be moved to the middle where the modules are back-to-back. The USB select could go there, too. Then each would be able to have a normal shield put on top.
i would rather buy a board with dip sockets. even if it was more expensive and bigger in size. just fried a microcontroller on my board and i'm very happy i can just put in a new one.
Hey guys -
I was wrestling with the layout last week and here's what I came up with.
http://magicsmoke.downingterrazas.com/wp-content/uploads/2009/05/multiduino-2layout.jpg
There are a couple notable things which differ from my sketched layout:
- Still no DC jack, I've got one picked and that corner of the layout is pretty wide open
- Arrangement of the CPUs is different, there was just no way to fit them in a 2x2 stack with a 2-layer board
- Arrangement of the CPU2-4 pinouts, again, just turned into a rats nest of wires in the earlier arrangement. Everything is spaced on 0.1 intervals so it's breadboard friendly.
- CPU select switch has been moved towards the middle for easier routing
- Few silkscreen items still missing (header next to CPU1 analog in is for I2C out)
Overall size is 3.3x5.95 with a little bite out of the top left corner. Only mounting holes are the standard three from Decimilia.
Only SMT components are the FT232RL chip, most caps, resistors, and LEDs. Everything else is through hole.
Once I wrap up a few final details I was going to get a quote for probably about 50x boards and I'll probably have the PCB house procure and solder on the SMT components. Depending on the interest I may also get some fully built with all thru holes done or at least order parts so they could be kitted.
If you're interested in a bare PCB, board + SMTs soldered, board + SMT + other components kitted, or finished PCB let me know.
crickets chirping
Anyone still interested in this?
wow :o