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Old 12-01-2015, 02:17 AM   #2418 (permalink)
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Originally Posted by MPaulHolmes View Post
Once it is initialized CAN is very easy to use. You can set up each node to ignore or accept whatever types of messages you want. Then, everybody just willy nilly blasts whatever the crap they want with no regard to concern about collisions. And they just accept whatever messages are for them. I have used it between a charger and several bms boards. Each board sent a packet of 8 bytes long, which were the 8 voltages of that bms module's 8 batteries. There were 6 modules just blasting their 8 bytes randomly and each ignored each others 8 bytes. The charger would pick up all the packets. No problems with noise and no missed packets (i dont think). And the data was never corrupted. You just use a little 8 pin $1 part along with the dspic CAN module.

I don't think it would take very long for it to be all proper with the standard packets. I just havent done that because i was trying to make interface with the user as cheap as possible. And I've never done any obd2 or whatever it is called. I just pictured people in a car repair shop with a greasy handheld device that read cryptic codes.
LOL - Actually the OBDII stuff does make wrenching quite a bit easier. I've got 2 code readers, one simply reads whatever you're interested in and displays that on a LCD. It does display the cryptic codes, but more importantly it also displays dynamic data. I use it on my Honda Insight to monitor stuff the dash doesn't display. The other one is a full code reader. It really made putting a new engine into my dad's Yota 4-runner possible. These new IC engines have sooooo many sensors that EV's with resolvers look positively simple by comparison. With the scanner I made sure all the systems were working properly; I can't imagine trying to guess at this stuff.

The reason I'm talking about OBDII at all is because the protocol works nicely for vehicles. Yes, the CAN bus doesn't need OBDII. But there are some nicely worked out message protocols that could be leveraged for our purposes.

It is a weird network, and it's ability to deal with random messages has a lot to do with it's robustness. Also, the differential signaling helps with noise. I think noise will be a major concern, especially with DIY EV's. No one in the DIY world cares about EMI until wierd "random" stuff starts happening.

That said, I really don't trust serial communications for critical inputs like throttle, etc. I'm trying to keep my use of it down to data acquisition and monitoring. Period.

- E*clipse
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