How do CAN Aux channels work?

[Josh18]

Hey all. I'm running an atom on my build and have basically run out of I/O.

I have been told about the CAN Aux feature, and am wanting to run a boost control solenoid off it.

My understanding of a bus like this is that each device has the bus protocol and its own address so it works in turn on the bus.

So I can understand how CAN devices like screens, lambda etc can run on the bus, but what I can't understand is how a "dumb" device like a bcs could run off the bus. Is it even possible or have I been told wrong?

Thanks in advance.

[essb00]

For most CAN expansions, the aux outputs are basic low current on/off triggers that cannot drive PWM...
Unless the CAN expansion is a PDM (power distribution module) --- which would be overkill for what you just intended.

You can assign the boost control solenoid on one of the AtomX's aux output for PWM, and then whatever you have there before that's just triggered on/off can be re-assigned to a CAN aux of something like ECUMaster CAN Switch Board V3.

[Adamw]

What engine?  If a 4 cyl direct spark you could possibly rewire the coils to wasted spark to free up 2 ignition outputs?  

[Josh18]

Hi adam, thanks. 

It's an Ej20 and I'm already on wasted spark. I'm sequential injection but I don't want to go batch fire. 

From memory my outputs, including the two free injector channels are

Fuel pump

Cel

Fan

Tacho

I can't remember the other two but I'm sure I've got six and used them all. Nothing funky, just standard stuff. 

I was thinking I could run the fuel pump off a switch to free up an aux. 

But I'm really curious if the CAN bus run an aux device like a bcs. It mentions it in the link help file but is pretty brief and I reckon I'm misunderstanding it. 

Cheers. 

Essboo, thanks. 

So could I drive the tacho or fuel pump relay for example from a CAN aux?

Im still confused as to how the can aux's control "dumb" components. 

Thanks. 

[essb00]

Tacho also has to be driven by PWM, basic fuel pump relay can be driven by CAN aux --- but since that is something critical that would cause a no-go whenever there's something up with the CAN switchboard or the CAN bus itself, I would personally want that driven by ECU aux.

[Adamw]

A "CAN aux" is just a piece of data in a CAN message that is sent to some other device.  So to make that into a real output that can drive a solenoid, you would need a CAN device that has outputs.  There arent too many low cost options that are capable of PWM control of a solenoid, most would be PDM type devices or "IO expanders".  

One example: https://mectricmse.com/en-nz/products/µpdm4-rev3

[Josh18]

Thanks Adam and Ess, that's pretty much the answer I was looking for. 

For it to work like I was told sounded like some kind of magic! What you guys have said is much closer to what I thought a data bus could do. 

I might just put my fuel pump on a switch and use that aux for the boost control. 

Thanks again.