DFH - Defacto FreeEMS Hardware in KICAD

[Fred]

Additionally, the ground from the VR sensors on the Toyota remains isolated from the main ground right up to the chip it is received at (very close to it). I suggest that we provide a ground pin and path for each critical sensor input that joins the main ground close to the point it is read.

The Toyota board is 2 layer also, and the way it is laid out is as follows :

A thick ground trace around the perimeter of the entire board. However! This does NOT form a loop (ground loop!) it is left open on one side.
Grounds for components in the middle come from "fingers" off the main trunk ground also avoiding any loops.
Finally, incoming grounds are coupled to the main ground via a small capacitor (as are all signals) right at the connector and only join the main ground in a "finger" like way where they need to.

I think the Toyota design makes a lot of sense in a lot of ways and I think we should learn from what they have done.

Fred.

[jharvey]

Sounds like it has a bunch of EMI protection. The ground going around the board makes for short antennas, the caps on the inputs are probably more for preventing RF out then they are for protecting RF in. These caps help make it FCC (or who ever ITU appoints in your area) compliant.

[Fred]

The ground going around the board makes for short antennas

Can you explain what you mean? The entire thing is wrapped in steel and ally from all sides except the connector area. I doubt there would be much EMI/RFI getting in there.

the caps on the inputs are probably more for preventing RF out then they are for protecting RF in.

Um, what would the source of the RF be from an ECU box that isnt' doing anything that would generate any? Secondly, if that was the case, why are they not present on all the outputs too? Only on signal/sensor inputs.

Fred.

[davebmw]

what you are referring to is called a guard ring, have a look here:

http://www.ce-mag.com/ce-mag.com/archiv ... E_028.html

[Fred]

Good link, cheers Dave.

[AbeFM]

Based on what I found inside the Toyota ECU (I trust Toyota) I'd like to see the values of the VR input circuit changed and an extra resistor added. I'd like to see 6.8k to ground for each VR input and 5.1k serial resistance (instead of 18k) with a larger 0.045uF capacitor on the inside. I guess so long as you add the extra resistor location I can put in different values quite happily.

Fred.

I'm a big fan of coping any OEM design that's known to work.

On the Mazda, they had caps in there - reading a digital signal - and it worked fine without them so in the end I took them out to get faster response. Why you don't all run miata VR-to-digital sensors, I dunno.


As to the driver, yes, leave off the diodes if the part will support it. The only 3 reasons I would leave them on are:
1) In case there's a pin-for-pin compatible alternative part without said protection (though see comment below)
2) To put an LED across the output just to watch it flash
2.5) A test point for clipping oscope leads

Comment Below: If the device should support it, and it's only there for paranoia of the end user (being paranoid myself I'd appreciate it), I still feel it's the idiot's job to do idiotic things on his own time. Certainly it would not be hard to just solder a diode right to the device, which is what I would do if I didn't trust you guys blindly with my life. Which I do, so no worries there.

I didn't actually read anything in this thread but page 6, so I'm going to try to get caught up now.

[AbeFM]

A picture is worth a thousand words there, mate.



Higher res available by request. I have another shot or two, but will take some of the whole board this weekend.

[Fred]

1) In case there's a pin-for-pin compatible alternative part without said protection

That is one good reason, however can you "just" drive a non logic level FET with a 5V CPU strength signal? I don't think so. Part of the reason to spec these devices is so that users don't have any trouble with them and also to cut back on component count. I think we should probably only support the protected stuff as it will probably save a lot of support headaches in the future (no company here remember, you people reading this ARE the support so this should bother you). Also not needing a driver chip saves space and complexity.

I would like to see a place for an LED on each output anyway if it is at all possible. it only needs to be led + resistor (possibly + diode).

Fred.

[Fred]

Higher res available by request. :-) I have another shot or two, but will take some of the whole board this weekend.

Perhaps start your own thread and link to it from here to prevent clutter. I'm currently uploading a stack of pics of the toy ecu. Will post shortly.

Fred.

[davebmw]

Totally agree with the auto protected logic level fets, Reduced component count makes every stage easier.
Any objections of uploading Bosch Motronic 3.3.1 pictures??