A new kind of board

Because it is impossible to use for example proto-board and LCD board in the same time and using Arduino in a piggy-pack with RaspBerry, I'd suggest a new kind of system bus

Use 40 pin IDE flat cable as a bus and use the same order of pins as in RaspBerry. Now the boards could be built interchangeable.
The boards should of course have 90deg DIL connectors to make the stack clean
The cable would allow you to use any kind of cards in a stack
It would allow you to open your stack of cards on your table and measure any of the cards without disturbing the others,
You could even build a power source card to the bus.

To make it still better there should be a card to connect the serial bus (RS232) of RaspBerry to Arduino. Now we can leave the USB-connection of Arduino for debugging and flashing and run the data connection without using USB line between the processor cards.
(at least I'm using Arduino as a programmable real-time GPIO for Raspi through USB-RS232)

There should also be backplane cards to add original Arduino (Uno / Mega) cards to the flat cable stack.

The format of the cards and the holes for the screws should be standardised in the beginning

Nice idea, I like it. I'm not quite sure how it would work if a Raspberry Pi is connected to an Arduino on the same bus. I can see that RX/TX would be connected to allow serial comms. How would other pins be connected?

It is difficult if not impossible to get support for new form factors, many have tried. However in this case it would be possible to create adapter board for Arduino shields, although that is a bit unwieldy. The connectors add to the cost.

Do you have any visual examples to show how cards would stack up?

Thank you for your comment.

No, I have no images. I had this kind of stack in bad old days when I was building a rather large laboratory system around VIC-20. It's a shame, I took no pictures.
One card was for counters, one for stepper drivers, another for RAM, another for ROM, one for 256kB of EMS memory etc. The stack was hold in form with long screws and pieces of plastic tube for spacers. For another version I made two vertical pieces of 5mm thick acryl with horisontal grooves holding the edges of the cards. So the cards were like floors between the opposite acryl walls

of course there must be some kind of bridge card to separate Arduino and Raspberry, if you want to use them both in the same bus. Still, in many cases it would be enough to connect only RX, TX, GND and power between RasPi and the Arduino stack. Here the bridge could be as simple as two connectors with lines connecting the abovementioned lines. Possibly also an IRQ and one or two data lines with jumpers

In some other situation you could use the stack with RasPi but without Arduino

My opinion is that the most important aspect of my idea is that with a bus like this you can use those combinations of cards, which are impossible in current architechture.

It would be great to have cards of size of about Arduino Nano with a standardized format.
Now there is a stream of cards from China with formats without any standard.
There should be some time for serious rethinking of the system.

The Nano seems rather small, with a 40 way connector that would take up half the board area. An Rpi/Uno size would seem to be more suitable.

It's impossible to impose any standard on boards coming out of China. I would instead be more flexible, as long as the cards have a 40 way connector and 4 mounting holes.

Have you looked at Microduino?

Yes, Nano is too small for some projects and the small size is not a good target. More important is that the boards are as easy to implement as possible and that everyone can either buy or build the boards she needs to make the system she wants.

I mentioned Nano as a reference, because you can fit the uP and the basic connectors there. I'd be totally satisfied with the size of UNO, but not the layout of the board. I have one UNO and it is totally useless, when you try to build something more complicated. I was rather pissed off when I found that I can not use but one card on top of the processor board.

Yes, I have checked this microduino and found no use to it in my use. They have had an extremely small system as their target. OK, the boards are small in two dimensions, so what ? The stack will be high.
This microduino is for those extremists, whose main need is something small like in robotics, aeronautics and some special laboratory equipement. Small size does not make it light, because you got to have connectors and spare space on every board.

  • The connectors are on three sides of the board. There is no way to use a normal proto-board nor breadboard without a special adapter board.

I believe most of the users of Arduino are looking for flexibility and light price more than extreme specs. Every project I have puilt so far around Arduino has been built in large boxes and been bolted to wall, car, mp or boat interior or inside some larger lab system.

There is another way to build this kind of multi board systems. Use serial links instead of paralell like in Arduino.
If you build a fast bus based on addressable RS232, I2C or something like CAN or even ethernet, you can easily collect your boards in any layout. The bridge stones are not expensive.
CAN bus would be ideal, because they have built the commands allready for the bus.
The system can be built around some router boards, who take care of the connections between the other boards.
Still there will be need for the 40pin flat cable bus between certain boards.

Arduino boards do not have addresses like for example DS1820. The address would make certain interactions easier.