AVR Freaks

Both ideas were out from my current field of view; which is nice. Many thanks! I feel a bit of respect (read fear) for the net protocol; for the case of the enc28j60, (*1)would it be possible to connect many devices to the line, as you would do with I2C, or would you need to have one enc28j60 per terminal? It would be quite nice being able to use networking to communicate among MCUs.

The CAN protocol looks really sweet. I am seeing about the MCP2515 chip that is available and well documented. However,(*2) how would you go about to segregate the communications? This protocol is build to make all the devices connected together, but in my case, I need each node to only know about his surrounding network; not the whole network. I guess this question goes as well for the enc28j60 protocol.

The two ways of doing this that I can think, are

• that each module would have two MCP2515 chips, one for the inputs and one for the outputs, thus isolating both of the networks. It will be a big over-spec. But who knows, maybe in the future I will need to abuse of the bandwidth of a single node's output/ input. (*3) I don't know however, if programming the Arduino to handle two MCP's will be to hairy.
• that all share the same bus. The contras are that I will need to figure out how one module will know that is the ID of the module that is supposedly connected to. There will also be a lot of bandwidth waste, as all modules will receive signals that they actually don't need. Probably in the case of having to use a common bus for all modules, will mean that I have to change my original design idea.

What are your better educated opinions, Kartman and awneil? (or well, actually anyone who knows)

I put these (*n) numbers to make it easier to locate particular questions. I hope this is a topic you enjoy discussing about :P

Many thanks!

Ok, so that rules the networking possibility out, because I plan to have many of these devices connected forming many small networks. That would mean that I would need to have many switches. It would be great that there was a way of making a low level switch for basic serial communications. Actually my first attempt, was to use a mux as a switch for serial, but it got very complicated quickly. My plan is to make cheap, small elements, so that's why I didn't just chose raspberries or arduino megas.

Doesn't it exist at all, some sort of Serial switch that can be on the board?

The CAN chips seem to be ok price and size, and now I am thinking on ways that I can try that in a protoboard. Can does use quite large messages anyhow. I am pondering wether the tradeoff of message lengths that CAN implies is superior to the tradeoff of using arduino megas.

yes! that is the idea... I am realizing how bad I am at explaining and contextualizing. I apologize.

Let's imagine I want to do this:

Where you started pressing the a button on the module that says bang, which sent a zero to the module that was connected downstream. This byte started propagating down, and changing depending on the module that it went through.

Well, making a modular calculator is a bit of an absurd application. My real intention is to make this, but with midi alike messages, and each module will have whatever user interface, and make changes to the midi note accordingly. It is not the type of communication system that you want to attain speed, but I expect that in the end there will be an element that is waiting for a midi clock signal to send the message, so the whole system is actually generating the data that will come out on the next clock and so on. But that is not the part I am most stuck with.

The idea is that plugging and unplugging these elements is something similar to patching modules in an eurorack modular rack; only that in this case it is digital data.

I did one single device that has a virtual modular environment inside, on a raspberry. It has an interface with buttons, and you can page between the modules, and connect them. It is totally an interesting thing that I am still expanding.

I also did a digital prototype for the idea that I am now trying to do physically (here) In the near future I want to implement this virtual prototype as a sort of back-end to design how the single device prototype operates. But I want to explore in parallel with physical elements, mainly because it is easier for people to understand the concept of "this objects that you plug together" than "a device that has a virtual modular environment that you can design using a client over http and using a single interface". Also these things may be used for music performance, so the physical objects allows a better interaction "bandwidth" than a virtual environment.

My final goal is to make a modules that you could actually buy/diy and integrate among; and keep creating new modules in the future.

I tend to think that there should be a way to multiplex a UART port if you can program the communication protocol on all of the ends. Today, searching a lot I realized that there is no ready made communication protocol for such a kind of network. Probably because it will never be the best way to communicate all the devices together.

I thought of a solution that I will be testing tomorrow, that consists on using a multiplexor, and having the nodes downstream to ask permission to send a message by setting a flag. I wrote the firmware just to think about it in more detail. (here) Tomorrow I should probably go step by step from simplest to more complex, until I get it working... hopefully. Otherwise I may think on just using the arduino Mega.

I actually was expecting that there would be a simple answer, like an cheap IC that would record any serial input and keep it (this, but cheap) or a protocol that can be applied easily with a library, as it is the case with I2C. I will keep posted on how it goes! And I can't thank enough for all the help that you guys have been giving me on this. :)