Create a C++ class to house all your data, with methods to set and get the data. The only way this data is written or read is through this class.

Now you have an easy way to know when a value has changed, since your code called a setter method. The setter method can call a private method in the class (or a friend class) to notify the other Arduino of the change. I would use I2C as nick suggested. You have the same class on the other end that reads the data and updates its copy.

This makes it sound easier than it is. If there is a master where the data always changes its not too bad to do. If the data can change on either end then you have to decide how to handle conflicts. Also, what if the data changes on side A while side B is in the process of using it? You'll need some kind of locking scheme.

I am actually working on something similar. The bulk of the data is on Arduino A and Arduino B is notified when a change happens. Data on Arduino B is in the nature of commands, so its not really the same data being changed.


 

The new Arduino WiFi shield looks interesting! But it begs the question... If it is using a AVR32 UC3 chip, which model is it?

Its an AT32UC3A1256(512)

Also it seems that having a ordinary 8bit AVR boss around a AVR32 chip seems a bit like the tail wagging the dog.

Not really. You use the right tool for the job. I looked into this a while ago, and the bottom line is that H&D Wireless makes a firmware library that goes with their wifi chip. The library does a ton of stuff, including implementing an entire TCP stack. This can not be done on an AVR, so the UC3 is needed to do all this.

Given all the work that has already gone into developing this board, would it not be a small step to go all the way and turn it into another board by designing one that makes this a total replacement for an UNO or Leonardo (sans the WiFi chip) and turn it into a much more powerful AVR based microcontroller? It would leave the 8 bit boards well behind and would go a long way towards releiving the long wait for the Due that has not arrived (yet). 
Since the chip on the WiFi board can have it's flash memory reprogrammed, It would seem the even the IDE is already mostly developed making the possibility of developing the board I describe a much more likely possibility. It would just be loading compile sketches that are not inteded to make the chip process the logic of a WiFi stack.
I wonder if the Arduino team has any such unannounced plans to bolster the AVR (vs SAM) line of boards.
Just wondering what others have thought? I'm curious.
Norm

You could of course build a 32bit board based on this or another UC3. There are piles of 32 bit boards based on various ARM chips and Microchip chips. The harder part is the software. You need a tool chain, libraries and all that. Atmel supplies all this for free (see AVR Studio) but its not Arduino compatible.
 

You're not ready yet to estimate per unit costs with any accuracy. You need to design a prototype. An Arduino Uno with shields is not a prototype. To get assembly quotes you'll need a list of components (BOM or bill or materials). You'll also need gerbers for the PCB and details about it (2 layer? 4 layer? Dimensions?).

That's the easy part. The harder part is the enclosure. Cost here is impossible to guess at without knowing anything about it.

Then there is final assembly and testing.  Then packaging.

Another big expense is shipping parts and assembled units around.

And tools. You'll probably need some hardware and software tools.

How about distribution chain? Are there distributors who sell to retailers? The price gets marked up each step of the way.

All that said, its all very doable. I did it, you can too.

 

eInk if the update rate isn't too high.

eInk would rock. But, I spoke with the eInk people. The minimum run is just absolutely huge, and I have not been able to find anyone selling eInk generic panels.

If you needed a graphical display that was about 2in by about 3in and readable in direct sunlight, what would you choose?

Atmel AVR ISP MKii still $34 tho.

Yeah but you only need one for a whole line of processors. I noticed the 1284P is down to about $8.50 quantity one! That's my favorite AVR.

Where did you find the enclosure?

After a bit of digging I found a place for super cheap PCB manufacturing.

http://www.oshpark.com/

I just checked their site, and one thing worth pointing out is that their boards are all ENIG, which means gold immersion. I order all my boards ENIG because I believe its well worth the extra expense. So if you compare prices to this place be sure the place you're comparing to also is quoting ENIG.

I have been happy with International Circuits, but that does not mean I won't at least look ;-)

Is that what all my "stop mask" errors are? Silk screen that overlaps something?

Looks like a great board, but what tool chain will be used to code for it?

Ok I will look around this kind of ship. Event buy 8 cards from http://www.strichlabs.com/products/multiserial-shield
is not expensive.

Well each card has 2 serial ports, so you'll only need 4 of them.

Ok, guess I was confused. Had the impression the multiserial shield used the same chip. Can't open its schematic from here.

The multi-serial shield does use the same chip... But both libraries work with multi-serial shield too...

That is the standard choice, and a good choice. Many years ago (don't ask) I build a radio teletype demodulator with that chip. It was used for ham radio RTTY over HF and VHF. Now, such things are nearly obsolete.

Is the DSS Circuits I2C library used with this?
Or is it one or the other?

Do you mean with this chip or with the MultiSerial shield?

Either the standard Wire library or the DSS Circuits library will work with this chip. I use the DSS Circuits library because I need to talk to this chip from inside an interrupt service routine (ISR). The Wire lib uses interrupts, and therefore can not be used inside an ISR. The DSS library does not use interrupts, so it can be used inside an ISR.

I hope I answered the question...

I found in old posts that you worked with that chip. Did you success on your project ?

Can you give us some schematics, or elements that will help me to realize it ?

Best Regards

I also found on the net : http://hackstrich.sarahemm.net/MultiSerial_Shield

May be it can be useful. Just have to remove Max232 chip and use max488. But I've to design it...

Yup, the project came out nicely. The hackstrich board is a great model, you can find Eagle files and code here:

http://www.strichlabs.com/pages/multiserial-shield