pulse width meter project

[Garfield Willis]

On Tue, 29 Aug 2000 13:11:42 -0700, Eric Aos <EOA at spartek.com> wrote:

>Not being an EE, my only point of reference for an automotive power supply
>has been the one for the EFI332 project. That one had a bunch of other stuff
>(techincal term) in it for protection from all the nasties. I have a PIC
>microcontroller, and a DP Ram chip. Again not being an EE, I'm not sure how
>clean a supply this is as opposed to how clean it needs to be... I did get
>the data sheet, and it looks easy enough to try.  

OK, gotcha; if you were asking "what other protection measures should
I take, besides an automotive supply regulator?", then any of that
other technoid "stuff" usually isn't spendy (lemme guess, filter caps,
inductors, ferrite beads, you name it), and better there than not.

The other thing that always goes without saying is, no matter how well
you protect the supply path, DON'T forget the signals. IOW, you see
Steve Ravet has placed opto-isolators in his signal paths. That's not
just a good idea for signal *noise* protection/ground shifts, but also
for transient protection.

You mention "how clean a supply"; not to be anal, but that's usually
referring to how free of *noise* the supply is, and just about ANY 5V
regulator will get you that far, if you use the recommended filter
caps on input and output of the regulator. Beyond that, the question
of "how safe" is the next issue, which admittedly often gets
confounded with the "how clean". Bluntly, the "cleanliness" has to do
with avoiding false signals (lost or phantom), and the "safetiness"
has to do with avoiding common automotive transients from KILLING your
circuit. Most of the protection features I mentioned with the LM2940
are to provide the *latter* sorta protection. So all that other stuff
you see in the EFI332 circuit probly wouldn't hurt as well.

If you'da said, "just how good is that protection *all by itself*", I
woulda known better how to respond; but hey, it's the hinternet, and
nobody's a mind-reader, so we grope around sometimes. :)

HTH,
Gar


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