Interconnecting Pics

logical · Joined: 21 Dec 2009 Posts: 57 Location: SouthPort, UK

Hi Guys/Gals

Possibly not relevant to this site but thought I would ask anyway.

Basically I cannot seem to make up my mind on the method to interface 2 separate pic chips.
They are going to be in an automotive environment with approx 2 metre cabling between then, will be using RJ11 or RJ45 (twisted pair) depending on how the mood strikes.

Looked at LIN (dismissed), CAN_Bus (interested), RS232 or Even SPI
Speed it not critical and the devices will be filtered from outside noise so should have an easy life.

Thanks in advance and have a great new year.

Chris

dyeatman · Joined: 06 Sep 2003 Posts: 1934 Location: Norman, OK

I'm not sure what you mean by "filtered from outside noise". You mean
filtered power or shielding?

For automotive applications CAN is the way to go, the automotive industry
spent millions figuring this out.

Radiated RFI is a major issue in the automotive environment due to the high
spark voltage. Neither RS232 or SPI are good choices due to the
environment.
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logical · Joined: 21 Dec 2009 Posts: 57 Location: SouthPort, UK

Guest · Posted: Thu Dec 31, 2009 7:17 pm

Just because a group spent millions on a system doesn't mean it is the best for your purpose.
Your application can be easily accomplished with RS-485 type chips or even a handful of discrete transistors.
I've had hundreds of energy control systems communicating over true single wire landlines for the past 20+ years using transistors. Something CAN Cannot do.

Jay

bkamen · Posted: Thu Dec 31, 2009 8:39 pm

You can also use products to avoid EMI like the fun stuff from Industrial Fiberoptics http://i-fiberoptics.com/Fiber_optic_led_photodetectors.php

RS232 runs great on this stuff.

Besides the previously mentioned balanced operation, this would work nice if the situation is point to point.

I suppose a ring topology could be fun too.

-Ben
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logical · Joined: 21 Dec 2009 Posts: 57 Location: SouthPort, UK

Thanks to dyeatman, ben and jay (not in a particular order!)

Think I will be going with the CAN Bus, fibre optic is a nice thought also, will bear that in mind for future projects where I need ultra speed and zero interference.

I especially like the CAN System, sure it's something new to learn BUT any upgrades for the system will be simple to add, (plug and pray :o) )

Looks like I gonna spend new years day designing some CAN Bus PCB's, got a boat load of parts to use and too tight to buy in evaluation boards, would mean waiting for the postal service.

Happy New Year to all.

Chris

bkamen · Posted: Thu Dec 31, 2009 8:53 pm

The fiber I pointed out isn't "ultra speed" -- it's more "ultra cheap" and "easy" as you can splice with a pocket knife.

It's 1000um plastic fiber. Fun stuff work with at low speeds without the hassle of terminating the ends.

But anyway..

Happy New Year!

-Ben
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Dazed and confused? I don't think so. Just "plain lost" will do. :D