new $EE tuning thing!

[RobertISaar]

as has been simulated and then tested real-world, the pulldown resistors in the A/D circuits can have a rather large effect on the linearity of a sensor read. either need more drive current(op-amp?) or more pulldown impedance, otherwise the linearity suffers and you need to build a table around known points.

[steveo]

otherwise the linearity suffers and you need to build a table around known points.

you're right. i'll do that for sure, probably as optional so people have a choice..

do you know what a typical curve would look like, or any data on tests other people have done? are we talking a curve down to a 0.25v dip in the middle or something? i could live with a percent but two or three might be bad news. other ecms must have similar circuits..

also wondering if the circuit for the a/c pressure input is of the same configuration as the other 5v inputs

i'm very happy to increase input accuracy with lookup tables. i already did that for temperature inputs. table lookups against an 8 bit value are very cheap when you have ram to play with, as long as you generate the table as a 256 byte array, the 'table lookup' is just a single address.

once my bench testing setup is working again, i'll grab a potentiometer and some voltage, and build a table.

[RobertISaar]

curve is going to be dependant on exact pulldown value and the sensor(or wideband controller or whatever is being read) itself.

typically, the a/c pressure sensor circuit is setup the same as a MAP sensor A/D channel, using a 51K pulldown. if you attach a 1K pot in place of the pressure sensor, any error is tiny, but if you were to use a 2K pot, you'll start seeing sag, a 5K is very noticeable and it just keeps getting worse. there seems to be good results when the pulldown is at least 40 times the impedance of the pot it is interacting with, or at least I was accepting that amount of error in my testing.

with a wideband controller making an analog voltage via either a digital-analog converter or just a PWM output run through a low-pass filter to approximate it(if there are other methods, I haven't seen them implemented in a wideband controller), hard to say what exactly any individual controller will produce without running it through some known values.

EDIT: a trick you may be able to pull off(not sure how easily) would be to model the differences that would occur with different pulldowns and maximum drive currents from the controller... I get the feeling that would be a bit complex though.

[steveo]

really, instead of a two-point calibration, i should have an optional three-point calibration. for example my wideband controller will output stoich for a particular fuel type when unplugged. that gives me a midpoint, and that should at least get it closer if i apply some curvature to it. i'm not great at math, but i'll fiddle around until i get it working.

edit: this will be next version stuff though, because holy crap i'm way ahead with features and way behind with testing.

[steveo]

more (beta 5): http://fbodytech.com/download/223/

one thing i've done in this version is (optionally) reduce display precision in the analyzer for fueling trims, yeliding a simple map of +2%, -3%, etc.. this allows a much more visually appealing and easier to work with map of your trims, rounding off tenths of percents that don't matter for VE tables anyways. also works for the new wideband vs afr target feature (if the patches work, of course)

some other cool stuff too, quite a few new settings....

details and changelog at http://fbodytech.com/3-6-beta/

[fbody_Brian]

Main tab trans display, gears 3 & 4 are reversed. It says I'm in 3 when in 4th and displays 4 when I'm in 3rd.

[steveo]

thanks, i'll fix that. i found the problem, i was reading this chart from the bottom up; and it's in a strange order. i'll assume that broke my shift selector since they use the same bits afaik

              SHIFT B  SHIFT A  GEAR
              ----------------------
                0        0       3RD
              ----------------------
                0        1       4TH
              ----------------------
                1        0       2ND
              ----------------------
                1        1       1ST
              ----------------------