I haven't used either I2C or SMBus but my understanding is that they are both essentially the same, the differences being small and relating to clock speeds and voltage levels. Also SMBus has an ALERT signal.

In either case there are no start "bits", there is a single start "condition" and two acknowledge bits.

SMBus is very well documented, have you searched for the spec and other documentation?

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Rob

Sorry, I'm sure this is simple but I'm not following it, in the above example wouldn't you just send the value 0x1F to shiftOut()? But then that doesn't give you a 120Hz modulated signal unless you feed that signal into the AND gate with the 120Hz on the other input.

How about a drawing of the required waveform or something.

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Rob

For one-offs and prototyping you can use the "dead bug" method, glue the chip upside down on some vero board and solder wires from the pins to the board.

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Rob

Finding an enclosure is in many ways the hardest part of a project, I've spent days trying to find the right one. You can start with these places

http://www.rose-bopla.com/index.htm
http://www.hammondmfg.com/index.htm
http://www.newageenclosures.com/
http://www.polycase.com/
http://www.china-mould.com/enindex.asp
http://www.serpac.com/default.aspx

I really try to use an enclosure where the manufacturer supplies 3D models as this help enormously with getting the PCB and component placement right, especially with odd-shaped boxes. Of the above I think Polycase, Hammond and Bopla do that.

China Mould (aka San He) have an amazing range many of which you may recognise from existing products and they will send samples if you have a courier account, but their site is crap and no 3D models.

Polycase and Bopla will machine and screen print the cases for you if you need special holes, logos etc, the others may as well but I've not asked.

May the force be with you, you'll need it

Do I need to offer some kind of firmware upgrades?

Probably, depending on the nature of the device. Try to make that a painless job for the user or you will get a lot of grief I suspect.

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Rob

VDDOUT is ~ 0.2 V ( Should be 1.8V) - This is not OK

The µC is overheating really fast - can't touch it in about 1 minute.

Current drawn ~ 550mA - This is way too much.

I would say you've cooked the CPU.

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Rob

which variables? A1 etc are #defines for the higher digital pins, starting from 14 IIRC so

digitalWrite (A1,HIGH);

is the same as

digitalWrite (15,HIGH);

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Rob

Oh, so you want to modulate a 120Hz signal, that's a different story.

That could be done all in software as well but it would be harder, in that case maybe going back to the 555 is the best thing for you.

You could run the 555 output to an AND gate and on the other input of the gate connect your data stream.

Then write a simple shiftout() function that shifts the bits in an array of bytes out one at a time with a delay between them.

I cannot see this sounding even vaguely like Twinkle... though, more like Morse code although with LEDs I guess you won't hear anything

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Rob

how could a resistor on the first device protect the second device if the cable between them is broken?

It can't. If the cable is broken all bets are off.

Note that most (all?) modern transceivers have fail-safe built in. How they do that without the parallel issues HugoPT was talking about I don't know, but they do. Probably some detection logic and FET switches or something.

BTW your FS resistor values are too low, I think abut 560R is typical. But as has been mentioned you can't have them on every node because they will all be in parallel, at least the ones to GND will be, not sure about the ones pulling high, depends on how everything is powered I think.

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Rob

Is that your video that shows the same display running on a Mega and a Due? Interesting to see the difference.

I am in the process of designing a Due-like board so am too busy to play with this for quite some time I suspect.

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Rob

Using a 555 actually complicates matters IMO because now you have to sync the CPU with the timer whereas the CPU can easily do all the work in code.

Is that a requirement as well?

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Rob

it seems that although CAN is present, there is no (official, at least) Arduino API to use it.

True, but there are a few people working on that and I even think it's sanctioned by the powers that be so it may wind up as official.

but I'm still open to other options that would help me.

I plan to use a Due for the "master" and the LPC11C24 for simple nodes, it has the controller and transceiver built in. Atmel have a CPU with the controller built in as well but no transceiver.

If your chips are just a few cm apart though I think I2C is probably the best option, I don't know it very well but it can do multi-master and that usually does NOT mean polling by a master because then it isn't multi-master

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Rob

True, but he hasn't mentioned 12v or LED strings or that he's pin bound. Is that the case JimiH?

Also where is this "text file" residing, do you have an SD card or getting the data from a PC?


EDIT:

I'm basically starting out using the "Shift Out" tutorial which uses shift registers and LED's.

Ok, that explains the shift reg, what about the text file?

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Rob

Any pointers here?

First thing, why do you need a shift register?

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Rob

UART and RS-485 are the same thing (sort of), RS-485 is not a protocol, it's just a physical layer you often use for UART comms.

How about CAN, that's multi-master, everyone just says what they want when they want and the hardware sorts the clashes out.

The Due has two CAN ports as well.

But how about some more details, speed and distance for example. Do they have to be AVR processors?

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Rob

I did look at this once before and IIRC the Ethernet part should work, but the SD card won't because it drops the expected 5v down to 3v3 just usign a voltage divider so if that starts with 3v3 it will drop even further to something like 2v1 and I doubt an SD card will work at that voltage.

Don't get the shield based on my memory though.

I've not looked but if this sort of information is not on the official pages it should be, it's pretty basic and for official shields at least people should be able to buy with certainty that something will work.

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Rob