Return of the diy_EGOmeter (YES, it's finally ALIVE!!)

[garfield at pilgrimhouse.com]

On Sun, 3 May 1998 11:39:37 -0700, "Robert Harris"
<bob at bobthecomputerguy.com> wrote:

>Having been led astray for the last few weeks, May I make a request?  To the
>developer of the wide range EGO, could you E-mail me privately (or on the
>list).  Need to know more about it.  Seems a certain low fangler that I
>sometimes correspond with has publicly blamed me for his new toy and now we
>need to tune it up at WOT.

Oh sire, wherein have you been led astray? Doth make for such a wide and
pithy lament, I know not what to reply. I trust t'weren't me that Pied
Piped you, since I tain't been here for the last few weeks. B)

OK, noughOdat nonsense. Time for another UPDATE, anyhoo. We've been
hoping for a couple weeks now to just turn the ole corner our
diyEGOmeter project has been hiding behind, and before I worry anyone,
NO, it's NOT "Houston, we have a problem", it's more like "Houston, I
can't seem to get my socks on". The circuit is all done, dressed up, but
with no place to go. Here's what's goin on.

Behind the scenes, Frank and I have been trying to build the "DIY
Standard Mark I Dragon Belch" device, an eXhaust gas simulator idea
Frank came up with, to make a burner pipe with O2 & T-couple bungs along
the length, and fired with a propane burner of goodly proportion,
allowing us a controllable range of mixture and temps for testing. NO,
it ain't gazolini-fired, but since we only wanna compare a known good
EGOmeter to our diy gizmo, I'd be to purpose.

Here's the deal, on which we have both agreed to withstand all arguments
should there be huesNcrys from the galleries. We are NOT gonna release
the schematic until we've had a go at testing the diyEgor side-by-side
the NTK standard one that Frank has, and run the diyThang through sweeps
of both rich and lean, to make sure it works OK and we don't infact have
anything unhappy to report back to Houston. The reason for the extra
caution is that NO MATTER how many people say, "Oh, well, just publish
the schematic and let us have a try", the fact remains that you would
HAVE to expense the $130someodd buckeroos to buy the sensor, and then IF
we found the circuit had some problem, our name's would be mud, bud. So
even if you say publically or privately ad infinitum, that you're in
such a rush that you can't wait till we test the thang to be sure, well,
just save yer breathNfingertips, cuz on this one we've sworn amongst
these Two Musketeers that we ain't gonna budge.

So what's the holdup? Well, we've both tried to build one of these
Dragon Belches, and it looks like the test apparatus might just be a
harder design problem than the dang meter itself! Hee, what a hoot. I
don't know exactly what kinda burner Frank tried, but I do know he had
some pals at UofMich in the Glassblowers Lab have a look at his Belch to
see what the problem was, but I got a commercial venturi burner used for
building kilns and small foundry furnaces, and BOTH of us can't get the
required range of mixture. I guess it's hard to make propane flames burn
"rich"? Dunno. So now we're considering other options for testing (one
of which is obviously we could put two opposed bungs in a stock auto
exhaust, and detune the engine to do our testing), and we WILL get there
soon, but the whole thing's kinda been stretched outta proportion, given
how FAST the design of the circuit came together in comparison.

Anyway, things ARE moving along pretty decent (compare this to how long
it took to get the 332 stuff together... I know, an unfair comparison,
this circuit is a fly-spec compared to the 332 stuff, but you see me
point?), and all I can say at this point is, there's JUST the final
testing to do, and then it'll be "soup". So that's not such a daunting
obstacle before us, and I trust we CAN all keep our shirts on until
that's done. OK, end of update.

Now, on to Robert's hint that he's in urgent need of more info cuz he
plans to use it in a closed-loop WOT setup. Mind you, as we've said
before, I'm gonna release the schematic for the basic "instrument" if
you will, that hopefully will produce an output curve of V vrs. O2 very
similar to the NTK box, since it passes the uncooked "Ion Pump Current"
turned into a voltage range from 0-5V on out as an output. Beyond THAT,
everyone with their own particular interests, be it "meters", or
data-logging meters, or closed-loop engine managers like Robert wants to
do, will need to layer ontop of this basic "instrument", their own
designs to accomplish their particular task.

For the time being, I would GUESS (again, since this ain't my primary
"locus of hocus pocus", exactly, I can only guestimate) that all you
need do for preparation to include the basic instrument in a closed loop
controller scheme is plan for the code to read the output V from Egor,
and map that to some value of AFR/Lambda. Beyond that basic concept, if
one wants to use a conventionally coded ECM that's looking for
"stoich-crossings", and your idea is to be able to "dial in" a
particular target AFR, this also seems quite easy, just a simple
comparator with a tiny bit of hysteresis to keep it from oscillating,
compare the basic Egor's output to your desired setpoint, and you'll
either get a rich or lean output from the comparator as your "pretend"
O2 sensor output, sorta re-defining stoich if you will. [BTW, this
concept wasn't my idea, of course. Someone on the group mentioned it in
passing one day, and I don't even remember who, if it matters to anyone.
Just don't intend this to make it sound like I thot that one up, thas
all].

I know that Bruce has some slightly more elaborate plans to use the
setpoint AFR idea, along with normal ECM control during lower power
demands on the engine. I mention this just to say that there are all
kinds of variations on a theme possible, but all yous guys need to know
at this point in your scheming, is that Egor will put out either 2.5 or
3.0V at stoich (you can choose; the NTK centers stoich around 3.0V cuz
that gives them a more even range of AFRs on both lean and rich sides),
but centering the output at 2.5V makes the circuit fewer parts and the
voltage references more solid. Beyond that, it's just a signal that goes
from 2.5/3.0 up to about 4.75V on the lean side, and down to near 0.25V
on the rich side. The curves on either side are fairly linear, but each
has a different slope, so for "measurement" purposes, you will need a
map or table of some sort, if you're using a micro. For those who want
to build a simple analog/led hand-held meter without the complexity of a
micro, I'll supply a two-piece linearizer circuit for ya. I DON'T think
we should build that into the basic Egor (we're not), like Horiba has
done, because any time you have linearization, you have temperature
coefficient errors from the scaling resistors, and if you're using a
micro, YOU don't need no stinking linearizer, nor the errors they can
introduce, both from the linearization itself, and the temp errors. Thas
why that decision.

OK, that's probably more than enough outta me for now. We'll keep ya
posted on how the testing's going. And I'll try to give ya updates at
least once a week now, until the Fat Lady sings. She'll be comin round
the mountain... (hmm, kinda mixing my music metphors there, eh?).

Cheers maties,
Gar