CAN daughterboard development

Marcos' unmaintained, but still in-use, Puma for FreeEMS circuit board/hardware design!
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KW1252
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CAN daughterboard development

Post by KW1252 »

I started a new topic of this since I didn't want to derail Marcos' thread more with the subject but kept it here as it's somewhat related project.

I'm still trying to figure out GIT so I'll just upload the KiCAD project. It probably won't load right up but there shouldn't be too much problems setting the project up. (the library manager COULD be a bit less nebulous...)

Anyway, this is how it should look like:
Image
Image

I figured there should be more options with the slope control than just a preset value to switch on or off, so I decided to put in a little resistor network. Using parallel resistors of different values would've probably saved a bit of PCB estate, but I decided to stick with this arrangement, because:

The free PCB space is dead space anyway;
Stocking a lot of resistors with different values isn't efficient for production;
Configuration is intuitive and simple;
You only have one shorting block to handle and don't need to store a bunch to be able to access all speeds.

Of course it would be possible to use a solid-state potentiometer with SPI or I2C for software configurable slope control, but I'm going to give Fred a break on that one :)

Errata: The pull-up resistor R1 should probably be closer to 1M than 47k, and the network resistors R5-R12 should be 10k each, not 20k. R4 pull-down is there in case a logic controlled standby mode is used; for switched 12v system it's most certainly not needed.
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nitrousnrg
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Re: CAN daughterboard development

Post by nitrousnrg »

Cool!
Git isn't rocket science once you start using it, but you might find yourself losing some time in trivial tasks. IMO it worths the hassle.

Hey, what if I put 5v in Puma's communication header? Its an easy modification.

To be honest, I don't know what is the purpose of fine tune the slope. Is that a way to have some control over the communication maximum speed? Maybe its related to noise immunity. I'm lost here.
EDIT: Ok, it was to reduce EMI emmisions. RTFM Marcos
Marcos
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KW1252
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Re: CAN daughterboard development

Post by KW1252 »

nitrousnrg wrote:Cool!
Git isn't rocket science once you start using it, but you might find yourself losing some time in trivial tasks. IMO it worths the hassle.

Hey, what if I put 5v in Puma's communication header? Its an easy modification.
By all means do, that would be a huge asset. A spare GPIO pin would be great too; it would be most useful for eventual SPI applications.
To be honest, I don't know what is the purpose of fine tune the slope. Is that a way to have some control over the communication maximum speed? Maybe its related to noise immunity. I'm lost here.
EDIT: Ok, it was to reduce EMI emmisions. RTFM Marcos
Heh, yep, that's what it's for ;)
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